Cover Crops for Natural Resource Management in West Africa (Book 2) by International Institute of Tropical Agriculture

Covercrop benefiWBdnefioes

$kt#?& de cwv-

cover crop produces large quantities of biomass that can be used as mulch. Furthermore, the legume is capable of restoring the fertility of degraded soils (Xulugalle et al. f 986, Osei-Bomu and Buckles 2993). The objective of this study was to determine the effects of M a m a ( M u m a pmiens var. utilis) and mulch management on the yield of dry-season okra and tomato.

Materials and methods The study a m Two separate on-farm experiments involving tomato and o h were conducted between 1998 and 1999 in the forest zone of Ghana.The study areas H1within the forest zone and have a bimodal mhikI1 pattern. The major season begins in April and ends in July, the minor season begins in September and ends in mid-November. The period between mid-November to March is the dry season. h the periutban areas many fanners practice a system of crop rotation involving green maize in the major season followed by natural fallow in the minor season and vegetables in the dry season.

The tomato study Four f m e r s participated in these trials, one farmer each at Apatrapa and Duase and two at Darko in the Ashanti Region of Ghana. The experimental design was a split p1of the main plot was type of fallow (hfucuna or grass), and the subplot was method of land preparation. M u m a was established in tbe major season of 1998, as an intercrop with maize at Darko and as sole crop at the other sites. Each treatment plot was 5.4 m x 5 m, having 6 rows of tomato of 5 m length 90 cm apart. Afucuna was established in the major season of 1998, as an intercrop with maize at Darko and as sole crop at the other sites. Intercropping was done simultaneously with maize by one of the fanners and the other farmer intercropped the legume 65 days after the maize (relay intercrop). Adjacent to the intercropped and sole cropped Mucuno was pure maize and grass fallow fields, respectively. The experimental fields were lei? to Mtlmyra and grass fallow (main plots) in the minor season. In mid-November, the fallow vegetation was slashed to ground level using a cutlass and the residues were managed as follows: * residue burnt and the soil ridged (burn & ridge) soil ridged and mulched with in-siN residue (ridge & mulch) * no burning and no tillage (zero-till); for Mucuna only. Each experiment was further split into two parts in a crisscross manner (Versteeg and Huijsrnan 1991); one part was fertilized, while the other was unfertilized. Tomato was transplanted in the last week of November. Water was applied to the crops at 3-day

SO Cavermps for natural resource managemenUPlanfes de wuvertum st gestion des ressoumesnaturelles

intervals at a rate of about 400 ml per hill in the evenings except during the days of rainfall. Fertilizer was applied at a rate of 125 kglha of NPK 15-15-1 5 1 week after transplanting followed by sulfate of ammonium at the same rate at flower bud stage. The quantity of biomass was assessed before land preparation by cutting all plant residues from four random areas per main plot. Soil samples for nutrient analysis were taken at a depth of 0-15 cm from the ridges (and on the flat for the zero till option) immediately after land preparation. Soil temperature and moisture content were measured at tomato flowering stage, which was the time most stress was observed. Soil temperature at a depth of 5 cm was assessed (once) during the morning at 8:00 GMT and during the afternoon at 1:00 GMT and moisture content was assessed immediately after a fall of rain and aRer 2 weeks without rainfall.

The okra study Unless otherwise stated, the procedure used in the okra trials was as described for the tomato trials. The experiments involving okra were conducted at Apemso in the Ejiso district. Ten farmers participated in the study, each representing one sitelreplication. All the experimental fields were under 1 year of Chrornolaena odorara fallow after 2 years of maize + cassava intercropping system. In June 1998, an area measuring 10 m x 20 rn was cleared out of each field by slashing with a cutlass. Immediately after clearing, Mucuna was planted as sole crop at a spacing of 90 x SO cm and left fallow until the end of the minor season. In mid-November, the Mucuna and a portion (10 m x 10 m) of the adjacent natural vegetation (C. odorata) were slashed to ground level using a cutlass. The Muntna plots were then divided into 2 equal parts making a total of 3 plots per site. After drying, the residues on one of the Maczlna plots were left as surface mulch while the remaining two plots were burned. The experimental treatments were therefore (i) Mzrcuna burned, (ii) C odorara burned, and (iii) Mucuna unburned. Okra was planted in the last week of November 1998 and harvested in February 1999.

Results and discussion Tomato trials Maize grain yieid and dry matter production in 1998 In 1998, M u m a completely overgrew and smothered the maize in the simultaneous intercropping system but had no effect on yield in the relay intercropping system. By November, M m a had accumulated between 1.5 t/ha and 5.6 t/ha of dry matter with a mean of 4.2 fia. The dry weight of grass ranged between 2.6 tha and 7.6 t/ha with a mean of 4.7 &a. It was visually observed that a significant (> 50%) part of these residues did not decompose before tomato was harvested due to the dry weather conditions.

Cover crop beneiitslBBnBf~wdm planfes da couv6Iture 51

Soil propetties Results of the soil analysis showed a higher level of potassium and organic carbon on the ridged plots compared with zero tillage but no difference in phosphow and nitrogen (Table 1). For the same method of laud preparation, soil nutrient status was consistently but not siguificantly higher on the burned plots than the unburned. There was also no significant effect of fallow vegetation on soil fertility. The piling up of topsoil may explain the apparent increase in fertility caused by ridging. Fallow on the other hand had no effect probably because the residue was not filly decomposed at the time of soil sampling. The soil temperatures and moisture content of the various management options are presented in Table 2. There were no significant differences in morning temperatures and moisture content of the soil soon after rainfail. However, afternoon temperatures were significantly lower and moisture content 2 weeks after no rainfall was higher on the mulched than the burned plots. Soil under zero titlage had the highest moisture content (13.5%) probably because the soil and mulch was least disturbed. Pests in tomato

Weed pressure in tomato was highest (883 k a a ) on the plots that were mulched with grass and lowest (66 kg/ha) on the zero ti I1 plot (Table 3). The reason for weed buildup in the grass mulch may include infestation of weed seed from the fallow vegetation and mulch material. Fire might have destroyed some of the weed seed and contributed to the reduction in weed incidence on the burned plol. Mucuna, on the other hand, effectively controlled the weeds during the fallow period and this might have reduced infestation and weed buildup. The mulch of the cover crop was however associated with insect pest problems. The insects (mainly ,orasshoppers and crickets) hid in the mulch and were responsible for the more than 40% seedlings damaged on the mulched Mucuna plots (Table 3). The relatively high incidence of pests in iWucuna mulch may be due to the fact that the mulch was more compact resulting In conditions more favorable to the insects. Tometa fruit yieM

Useful data on tonlato yield were obtained from 3 farms. At Darko the farmer who intercropped Muc~inasimultaneously with maize lost the crops on the entire experimental field due to fingal diseases. The other farmer lost the plot that was mulched with ,ms through accidental fire. There was also crop failure of tomato on the zero-till plot at Apatrapa due to destruction of the seedlings by insects. The unfertilized portion of the trial at Duase failed probably due to low soil fertility. Because of these losses, data on yietd could not be combined and analyzed. The yields from the individual farms are presented in Table 4. At Darko h i t yields without fertilizer ranged from 400 kdha to 1037 kgka, the corresponding yields with fertilizer

52 Covetcmpsfornaml resource managemenWlantef decmmmre etgesbon des ressarrces nahmsIes

Tabte 1. Elfectof fallaw vegetationand method of land preparationon soil nutrientstatus(0-1 5 cm depth) in four on-farm tamafo trials.

fx. K (-lfig)

Total N

("/I

(%I

Grass burn & ridge Grass ridge & muteh Mur:una bum & n'dge MUCEIR~ ridge & mulch Mucunazero till

cv % LSD (0.05)

Table 2 Soil temperature (OC) and moistureantent (%) at 1 em depth as affected by fallow vegetation and method of land preparation. --

Sail temperature 8:OO 13:OO Grass bum & ridge Grass ridge & mulch Mucuna bum & ridge Mucuna ridge & mulch Mucunazero till

20.0 21.8 19.8 20.8

CV% LSD (0.05)

Soil moisturea

21.5

35.0 26.5 31.Q 27.0 25.5

14.3 16.5 14.5 14.4 t 5.9

13.5

2.5 ns

5.5 4.5

9.2 ns

8.2 2.4

8.4 11.3 10.7

11.2

'Soil moisture 1 assessed soon after rainfall and soil moisture 2 assessed after 2 weeks without rainfall.

Tabte 3. Tomato establishmentand weed dry weight as affected byfaRw vegetation and method of land preparation.

T~atment Grass bum & ridge Grass ridge & mulch Mucuna bum & ridge Mucune ridge & mulch Mucuna zero till

CV % LSD 10.05)

Stand (PibW

%~efif~

Weed a Oc9rna)

6.1 5.4 6.3 6.2 5.5

14 13 19 42 39

269 833 207 97 66

12.7 ns

29 18

23.6 191

Cover crop beneCWBBnt3idesdes @antes de wuverture 53

were 586 kg/ha and 1900kg/ha. For both &e fertilized and unfertilized plots, burning the grass gave the lowest yields while zero tillage gave the highest yields. Yields at the other villages were relatively low and the trend was inconsistent. Low yields may be attributed to water stress because these trials were relatively far from the valley bottom and had drier soil conditions. In these villages tomato with fertilizer also yielded the highest on the ridged-and-mukhed Mumna plots. Okra friaIs

Useful data on okra were obtained &om seven sites and data are combined and presented in Table 5. Soil temperature ranged fiom 3 3 . 6 O C to 272O C and moistutr: content &om 8.1 % to 12.1%. The lowest temperature and highest moisarrr:content was recorded on the unburned plots with no significant difference among the burned plots. There was however lower plant establishment on the unburned plots and this was mainly due to insect pests on the seedlings. As a result, replanting was required several times in order to improve plant stand on the mulched plots. Plant height ranged from 5 2.3 cm to 73.3 cm and fruit yield from 1712 kgha to 4031 kgha (Table 5). Tfie highest yield was obtained from the mulched plots with no significant difference among the burned plots. Mulching therefore increased h i t yield more than 100% compared with planting on the bare soil. Lower soil temperatures and increased moisture retention in the soif may account for the high yield. Table 4. Effect of fallow vegetation and method of land preparation on yield (kglha) of tomato.

Wrth fertilizer

Without fertilizer Treatment

Darko

Grass bum & ridge Grass ridge & mulch Mucuna bum & ridge Mucuna ridge & mulch Mucuna 'zero till

400

Aoaira~a 267 378 587 375

1012 950 1037

Darko

Duase

568

512 518 600 632 593

962 1625 1900

Auatra~a 443 668 381 78 1

Table 5. Effect of fallow and mulch managementon soil moisture content (SMC), and soil temperature, and yield of okra in 1998-99 dry season. SMC Treatment

(%I

Temp.

(%I

Density (Plts/m2)

Height (cm)

(kgha) 1712 1843 4031

Chmmo!aenabumed Mucuna burned Mucma not burned

8.1 8.7 12.1

33.5 34.0 26.5

4.1 5.3 3.6

51.3 63.5 73.3

CV % LSD (0.05)

16.1 2.3

5.3 2.5

7.7 0.5

5.2 5.6

Yield

17.5 0.81

Cover cmps for natural resource managemenP1antes Ue wuverhrreel g w b n Ues ressources naWeIes

Conclusion It appears from these studies that soil moisture and temperature rather thaa soil

nutrients may be the most important factors determining yields for dry-season vegetables.

Acknowledgments The authors are grateful to the National Agricultural Research Project and the Natural Resources Institute of UK (under the DFID Kumasi Natural Resources Management Project) for providing funds for the okra and tomato trials, respectively.

References Carsky, R.J., Y. Hayashi, and G. Tian. 1998. Benefits of mulching in the subhumid savanna zone: research needs and technology targeting. Resource and Crop Management Research Monograph No. 26. International institute of Tropical Agriculmre, Ibadan, Nigeria. Nulugalle, N.R.,R. Lal, and C.H.H.Ter Kuile. 1986. Amelioration of soil physical properties by Mucuna after mechanized land clearing of a tropical rain forest. Soil Science 141:219-224. Kwapata, M.B. 1991. Response of contrastingtomato cultivars to depth of applied mulch and irrigation frequency under hot dry tropical conditions. Tropical Agriculture (Trinidad and Tobago) 68: 301-303. Lal, R. 1993. Technological options towards sustainable agriculture for diEerent ecological regions of sub-Saharan Africa. Pages 295308 in Technologies for sustainable agriculture in the tropics, edited by J. Ragland and R. Lal. American Society of Agronomy, Madison, WI, USA. ASA Special Publication No. 56. Nakashima, 1,K Hida, W. Zhou, and K Lai. 1391. Studies on stress tolerance of vegetables in China: eEat of cover materials on growth and yield of sweet pepper. Agriculture Research Series (Japan) 23: 192-196. Osei-Bonsy E? and D. Buckles. 1993. Controllingweeds and improving soil fertility through the use of cover crops: experience with Mwnn spp. h Benin and Ghana. West African Farming Systems Research Network Bulletin 14: 2-7. Shajari, kR,M.Gueye, J. Yonemura, and A. Sasoa 1990. Research on water saving on sandy soil indrip irrigation(2). Mulching, temperature control, and crop production in drip irrigation. AgricuItd Mechanization inAsia, Africa, and Latin America (Japan) 21: 25-28.

MN.and A. Huijsman. 1991. Trial &ign and analysesfor on-farm adaptiveresear* the 1988 maize trial in the Mono province of Benin. Pages 111-121 in On-fm research in theory and practiw, edited by H.J.W. Mutsaers md P. Walker. InA,Ibadan, Nigeria V-g,

Persistence of Mucuna pruriens biomass during the dry season along an agroecological transect in Benin

The persistence of M u m a biomass was observed in three sites in the Benin Republic during the dry season of 299748 At Paakou, in the southern Guinea savanna agroecological zone ofnor&ern Benin, Mumcnadry matter (DM) decreased at a rate of approximately 0.2 thdmonth. At the onset of the next rainy season, an early Munula ( M u m a p ~ ~ ~ var. i e mutiIis Rajada) cultivar had less tIran 2 t DMha and late varieties (Mucvna pmiens var. utiiris, Preta, and cochinchinewis).bad more than 4 tma. In southern Benin, Mucuna dry matter increased significantlyat Hayakpa, a nonde&raded site on the Allada Plateau, and remained comtant at Adim@gon, a highly degraded site on the Abomey Plateau. At the onset of the subsequent rainy season, Mucuna dry matter averaged 6.0 t/ha at Hayakpa and 4.7 tlha at Adingnigon. Prediction of growth and persistence of M a m a must take into accost the duration of the variety, the soil characteristics, the agroecological zone, planting date, and crop associations during the establishment phase. The Munula Mlow system should be primarily for weed suppression where its biomass is likely to persist. This is IlTA manuscript number LITM99JCPDO.

56 Cover cmps ibr nafutat m o m managemenllPanfesde cawmre et gestion des resources nahrrenes

La persistance de la biomasse de M u m a a 6th observde dans trois sites en Rdpublique du Benin au cows de la saison seche de 1997-98. A Parakou, dans la zone agro&cologiquede la savane sud guindenne, la matiere seche de M m n a a baissd 3 un taux d'environ 0,2 thalmois. Db le debut de la saison des pluies suivante, un cultivar de Mumna precoce (Muwna spp. Rajada) a eu moins de 2 tonnes de m a t i h s dchesha et les varietds tardives (var. utilis, Preta et cochinchr'nemis) ont eu pius de 4 tha. Dans le sud du Benin, la matiere seche de M u c m a augment6 de maniere significative B Hayakpa, un site non dkgrad6 situd dans le plateau d'Allada et elle est restCe constante B Adingnigon, un site fortement degrade dans le plateau d'Abomey. Au debut de la saison des pluies suivantes, la matiere s&chede Mucuna a atteint une moyenne de 6,Ou ha I Hayakpa et 4,7 tlha & Adingnigon. Les previsions de croissance et de persistance de Mucuna doivent tenk compte du cycle de la variktk, des caracteristiquesdu sol, de la zone agroecologique, de la date de semis et des associations wlturales pendant la phase d'dtablissement Le systkme de jachkre de ~2(CZ#ZQ doit d'abord viser la suppression des adventices Iorsqu'il existe une probabilit6 de persistance de sa biomasse.

Introduction Muntnepmriem cover crop fallow is a promising way to protect the soil and suppress weeds (Carsky et al. 1998, Vissoh et al. 1998). Benefits of Mgcuna include weed suppression and soil protection, among others (Becker and Johnson 1998). Tbe most important time to protect the soil in the Guinea savanna zone is at the beginning of the rainy season (Carsby et al. 1999%Mailer-Swam and Kotschi 1997) as it is characterized by intensive rains and wind, resuiting in substantid movement of soil (Carsky and Ndikawa 1998, Adeoye 2986). A preliminary study (one field) in the northern Guinea savanna of n o h e m Nigefia gave an estimate of disappearance of Mucun~mulch of approximately I Vhdmonth (Carsky et al. 1998) resulting in loss of at least 50% ofthe Mucmma dry matter. In more humid savanna zones, sparse raios during the dry season may stimulate emergence, growth, and reproduction of some weed species. This process cm be prevented by maintaining a mulch cover dllting the dry season. A study was undertaken in three sites in Benin Republic to observe the persistence of M~rnna biomass during the dry season of 1997-95. The objective was to estimate the rate of disappearance of Munma mulch and measure the amount leR on the soil surface at the time of land preparation.

Cover crop benefiW6n8ficesdes plantes 0'scouvertm 57

Materials and methods The two sites in the derived savanna of southern Benin were Hayakpa village (approx. 2"07' E, 6"34' N) on the Allada Plateau (early stage of degradation) and Adingnigon village (2"01' E; 7"05' N) on the Abomey Plateau (late stage of degradation). Soil properties at the sites (Table 1) show that plant available P (Bray-1 extract) and exchangeabie K were moderate at Hayakpa and low at Adingnigon. At Wayakca there were 9 fields in which Mrccvna cochivlchinensis was planted into maize or a maizecassava intercrop in June or July. At Admgnigon, M. cochinchinensis was grown as a sole crop and there were six fields in which the vegetation was not burned during the dry season. Monthly rainfall at the sites is given in Table 2. A site in northern Benin consisted of a seed production farm near Parakou (2"4 1'E; g023'N) and a research station near Ina {Z042' Q 9O58'N). Mucyna seed multiplication plots contracted by the Centre d'information et d'echangs sur les planies de couverture en Afrique (CIEPCA) were sampled. There were six fields of a short duration variety (M. pnviens var. Rajada) and six fields of long duration types (M. pnuiens var. uti'is, M. pruriens var. Preta, and M. cochinchimewis).Cattle were kept out of the fields by station guards. At all sites, two 1 mZquadrats per field were used to sample total aboveground biomass at four times ducing the dry season of 1997-98. In the northern site, pods were part of the first sample but not subsequent samples. A subsample of biomass was retained for gravimetric determination of moisture content. At the fmt samplmg time, Table 1. Soil characteristics at sites in southern Benin Republic.

Bray-1 P Site Adingnigon Hayakpa Pmb for t-test

PH(KCI)

6.01 6.23 0.09

(~g$) 3.1 6.4 0.025

&K (cmoW1 0.09 0.17 0.004

Table 2. Monthly rainfall (mm) at the sites. Month

October 1997 November 4 997 December 1997 January 1998 February 1998 March 1998 April 1998

Hayakpa

Adingnigon

InalParakou

205 63

290 0

125 0

0 17

0 66 0 94

9 3 10

0 59

Benin data from: BuUe%nAgrometeorlogique Decadaire. Ministere des Travaw: Publics et de Transports. D i d o n de la Meieoralagie. BP 379 Cctonou, Republigue du Benin.

58 Cover crops for natural resource managementIPlantes de couverture et gestlon des ressoun:es naturefles

root biomass was collected to 0.2 m depth using 4 rectangular cores measuring 0.1 m' of surface area and 0.1 m depth. Means were calculated for each site and sampling date, including 2 Mucuna varieties at the northern site. Data for the northern site were analyzed separately from those of the southern sites. At the northern site, VARIETY and sampling DATE were retained in the analysis using Proc GLM in SAS. In the south, SITE and sampling DATE were retained.

Results and discussion In the northern Guinea savanna site, dry matter of both varieties of Mucuna decreased during the dry season (Table 3). The long duration varieties had significantly more dry matter (averaging 6.3 tlha) than the short duration variety (4.4 tlha) at the beginning of the dry season. In both varieties, the largest decrease occurred between the first and second sampling period when seed was harvested. Subsequent loss of dry matter from late January to late April was 0.4 tlha for the late varieties and 1.0 tlha for the early one. In the ANOVA there was no significant interaction of variety and sampling date so the rate of loss of dry matter was not significantly different between the varieties. The amount of mulch remaining for the short duration variety (less than 2 tlha) may not be sufficient to protect the soil from the violent winds and intense rains that often occur at the beginning of the rainy season. In the derived savanna, Mucuna dry matter was initially lower in the nondegraded site (Table 4). This is because all farmers planted the Mucuna into a maize crop later in the year, while it was grown as a sole crop at the highly degraded site. Subsequent drymatter evolution reveals that there was some growth at both sites during the dry season. Accumulation of additional dry matter between early December and late March was approximately 3 tlha at the less degraded site and less than 1.5 tlha at the highly degraded site. The site by sampling date interaction was significant (P < 0.05).

Table 3. Persistence of Mucuna dry matter (tlha) during the dry season in the northern Guinea savanna of northern Benin as a function of maturity cycle of the varieties. Sampling date Maturity of vartely

2112197

21/1198

Late Early Mean SE vartely SE Date

6.26 a 4.41 a

4.78b 2.81 b 3.80

5.34

5/3/98 4.61 b 2.32 be 3.47

2214198 4.36b 1.80e 3.08

Mean 5.00

2.84 0.162

0.230

Means for a variety (within a row) followed by the same letter are not Significantly different. Harvest of pods between first and second sampling date (approx. 1.3 t DMIha for early variety and approx. 3 t DMlha for late varieties).

Covercrop banefi8r18fic~s des @antes de couverture 59

Table 4. Evolution af Mucuna dry matter (tlha) in the derived savanna d southern Benin as a function rtf soil degmdalion at the sites. -

Sage of degradation

19111/97

fly Late

3.045 3.379

SE ISiWDatel

0.081

Sam~linadate WlJ98 1512.498 7.21 4.57

5.81 3.49 - -

24W98

5.98 4.67

Note: Mucuna planted in asso&on with m a & ? andlar cassava at the less degraded siteGd as a a i stand at the more degraded Bte.

Differences in dry-matter accumulation were due to differences in soil properties (Table I ) more than differences in dry-season rainfill (Table 2). The evolution of Mvcuna dry matter in the southern sites was very digerent from the northern site. While M v m a dry matter decreased over time in the northern site, it increased during the dry season at the southern sites. The rate of disappearawe of Mucuna dry maEer after grain harvest at the northern site was 0.1 to 0.3 tlhdmonth, much less than that observed by Carsky et al. (1998) at Bauchi in northern Nigeria (Fig. 1). This is partly due to differences in rainfall. Bauchi, in the no&ern Guinea savanna, normally receives only traces of rain from October to April, while Patakou received some rain in January, March,and April (Table 2). Long-term data suggest that length of the dry season is 295 days at Bauchi, 165 days at InalParakou, 105 days at Adingnigon, and 95 days at Hayakpa (Jagtap, no date). Disappearance of Munsno mulch in the northern Guinea savanna (6-month dry season) or Sudan savanna zones (?'-month dry season) is substantial. M u m u mulch will only partially protect the soil from the impact of early season rain and wind erosion. It supplies a small amount of nutrients, equivalent to 5 to 15 kg Nka as fertilizer (Carsky et al. 1999b). Mucuna mulch is not sufficient to suppress weed growth under these conditions. On the other hand, in the derived savanna, where the relatively short dry season is broken by several isolated showers of rain, M m a biomass persists in suEcient quantity to suppress weeds. Mean root dry matter from 0 to 20 cm depth was approximately 400 kgha for M. cochinchinensis, 200 kgha for M.pmtiens var. utiis, and less than 100 kg/ha for M. pmiens war. Raja&. This resulted in root-shoot ratios of 8 to 24% for M.cochinchinensis and 4% or less for M pm~iensvar. utilis and M.pwjeirp var. Rajada (Table 5). Root recovery may have been reduced in the northern sites because of the more gravelly soil. M. pruriens var. Rajada roots may have been already senescing.

Conclusion This work allows us to understand that the potential for beneficial mulch effects from a promising cover crop varies with length of growing period and len-4 of dry season,

60 Cover crops fDr natural resoume rnanagementlPlanfesde comrture et gesfion des ressources narurelles

Table 6. Root-shoot ratio for three Mucuna varieties at three sites at the beginning of the dry season in Benin 1997.

Mcuna variety

Hayakpa

Adingnigon

InaIParakou

Rajada

+6.5 months

---0--3 months-fertile

+3.5 months-degraded

5 months

Bâ&#x201A;Ź

2? a

0 0

100

150

200

Days aRec November 1 Figure 1. Evolution of Mucuna dry matter during the dry season as a anction of length of dry season and soil fertility. Data for 6 month dry season fromCarsky et al. (1999).

the duration of the Muczrna variety, the cropping system (sole vs. intercrop), and the level of soil degradation. it suggests that early varieties of Mst~mado not accumulate sufficient biomass to provide an adequate amount of mulch after a 5-month dry season whik long-duration varieties do. Mucuna dry-matter persistence varies substantially between agroecological zones. Extrapolation of results across agroecological zones must be done very carefully. Likewise, targeting the use of the Mucuna short-fallow system should take the persistence of Mucum into account.

Cover crop benefiWBBn6rices d'es plantes de muverture 61

References Adeoye, K.B. 1986. Physical changes induced by rainfall in the surface layer of an Alfisol, northern Nigeria. Geoderma 39: 59-66. Becker, M. and D. Johnson. 1998. The role of legume fallow in intensified upland rice-based cropping systems in West Africa Nutrient Cycling in Agraecosystems. 6: 1-1 I . Carsky, R.J. and R. Ndikawa 1998. Screening multiple-use cover crops for the Sudan savanna of northern Cameroon. Pages 179-187 in Cover crops in West Afiica: contributing to sustainable Agriculture, edited by D. Buckles, A. Eteka, 0.Osiname, M. Galiba, and G.Galiano. IDRC, Ottawa, Canada. Carsky, R.J., S.A. Tamwali, M. Becker, D. Chikoye, G-Tian, andN. Sanginga 1998. Mucumherbaceous cover legume with potential for multiple uses. Resource and Crop Management Research Monograph No. 25, ITTA, Ibadan, Nigeria. 52 pp.

Carsky, R.J., Y. Hayashi, md G. Tim. 1999a. Benefits of mulching in ?he subhumid savanna zone: research needs and technology targeting. Resource and Crop Management Research Monograph No. 26, IITA, Ibadan, Nigeria Carsky, R.J, B. Oyewole, and C. Tian. 1999b. integrated soil management for the s a v m a zone of West Africa: legume rotation and fertilizer N. Nutrient Cycling in Agricultural Systems 55:

95-105. Jagtap, S.S. No date. Information system for sustainable agricultural development(INF0). Electronic database. Agroecological Studies Unit, IlfA, [badan, Nigeria Mikller-Siimann, K.M and J. Kotschi. 1997. Sustaining growth Soil fertility management in tropical Smdlholdings. Margraf Verlag, Weikersheim, Germany. Vissoh, P.V., V.M. Manyong, R.J. Carsky, P.Osei-Bonsu, and M. Galiba 1998. Green manure cover crop systems in West Africa: experiences with Mucum. Pages 1-32 k Cover crops L West Africa: contributing to sustainable agriculture, edited by D. Buckles, k Eteka, 0. Osiname, M. Galiba, and G. Galiano. IDRC, Ottawa, Canada.

Response of hperata cylindrlea to smothering by different Mucuna accessions D. Chikope md E Ekekme International lnstrtttte of Tropical Agriculture. Ibadan. Nigeria

Ten Mucuna accessions were evaluated for their ability to suppress speargrass in the forest-savanna transition zone of Nigeria in 1997 and 1998. Seedling density of all accessions 1 week after sowing (WAS) was less than 50% of the targeted Mucuna population. In 1997, all accessions covered the ground fully (> 80% of ground covered) 10-12 WAS except Mrict~napruriens var. ucilis which covered the ground fully 14 WAS. In 1998, all accessions covered the ground fully 8-10 WAS. Except Muctrna spp. Ghana and Rajada, which senesced mid-season, all accessions persisted for 6-8 months. Averaged over 2 years, M. cochinchinensis, Mucuna spp. Jaspeada, and Miicrtna spp. Veracrut (mottled and white seeded) were superior in biomass production than the rest of the accessions. M. pruriem var. utifis and Mtrcurra spp. Rajada were the poorest biomass producers. Afier 2 years of sowing cover crops, all accessions reduced speargrass biomass compared to the initial stand in 1997. M. cochinchinensis, M N C U ~ spp. U Jaspeada, and Mucuna spp. Veracruz (mottled and white seeded) reduced the biomass of speargrass most while M u m a spp. Preta and Mucuna spp. Rajada were the least effective.

R&srmB Dix obtentions de M~rcunaon&itC Cvalukes pour leur capacite a supprimer irnperata dans la zone de for& arbustive du Nigeria eTr 1997 et 1998. A 1 semaine apri?s le semis (SAS), la densit6 de population des planrules de toutes les obtentions etait moins de 50% de la population de Mrrcrrna ciblee. En 1997, toutes les obtentions avaient totalement recouvert le sol (>SO% de couverture du sol) A 1&I2 SAS, A l'exception de Mtrcrlna pnrriens var. uiilis qui n'a recouvert totalement le sol qu'A 14 SAS. En 1998, toutes Ies obtentions ont totalement recouvert le sol a 8-10 SAS. A I'exception de Muczitza spp. Ghana et Rajada qui ont subi une sknescence la mi-campagne, toutes les obtentions ont persiste pendant 6-8 mois. t e s moyennes pendant deux ans indiquent que M. cochinchinensis, Mrrczrna spp. Jaspeada et M m n a spp.Veracmz This is I U A manuscript number llTA/99/CP/17. 62

Cover crcp bonefits/BBn8fi#s des plant& de inuverture 65

(varietbs bigarrees et B graines blanches) ont eu une production de biomasse suptrieure A celle du reste des obtentions. M. pruriens vw. u!iJis et Mucma spp. Rajada ont eu la production de biomasse la plus faible. Apr5s deux anndes de culture de plantes de couverture. toutes les obtentions ont permis de reduire la production de biomasse d'imperata contrairemeat aux premieres plantes utilistes en 1997. A!. cocl~inchble~sis, Muclrna spp. Jaspeada et Mucuila spp. Veracrut (varietes bigarrkes et a graines blanches) ont le plus rdduit la biomasse d'imperata m d i s que Mucuna spp. Preta et Mucuna spp. Rajada dtaient les moins eficaces.

In West Africa, speaerass [Impernla cyiindrica &.) Rauesch.] is' one of the most abundant, competitive, and difficult weeds to control in areas where land is cultivated intensively or in natural bush hllows that are frequently exposed to burning (Garrity et al. 2997). Smothering by cover crops is one of the most promising techologies for alleviating problems associated with speargrass infestation in small-scale farms (Udensi et al. 1999, Versteeg et al. 1998, Vissoh et al. 1998). M u m a species are prominent among the cover crops that have been promoted for speargrass and fertility management in West Africa (Versteeg et al. 1998). Of the many known accessions of Mucuna worldwide (Wilmot-Dear 1992), only Muczma pvwieas (L.) DC. var, utilis (Wright) Burck and to a lesser extent Mucuna cockinchinensis (Lour.) A. Chev. have been extensively tested for weed and soil management in West Africa (Udensi et d. 1999, Versteeg et al. 1998, Vissoh et al. 1998). Reasons for the failure to test other accessions of Mucuna may be due to lack of seed. Reliance on a few accessions can lead to increased disease and pest pressure that can reduce the effectivenessof M u m 4 after prolonged use on the same field. For example, a foliar disease caused by Macrophominaphmeoiina was observed in Nigeria after many years of using M u m a pmriem var. utifis on the same plots (Berner et al. 1992). It has also been observed that the response of speargrass to Mvcuna spp. can be variable. For example, Akobundu et al. (2999) found that M. cochinchinensis reduced the density of speargrass better than M. pnrriens. Several authors have reported that some species of M u m a grow poorly when planted in a number of soils (Hauiah et al. 1991, Sanginga et al. 1996). M. pruriens var. utilis, which has been adopted widely for the suppressionof speargrass in southern Benin, grows poorly in some fields within the same zone (A. Okogun, personal communication). Reasons for the lack of or poor establishment of Mucwla reported in West Africa are not well understood. Good establishment of Mumna is a prerequisite for eflective weed control in any cropping system. The morphological and physiological characteristics of Munura which contribute to weed suppression are good germination and early vigor, high

64 Covercmps for nafuml resouree managemenVPlantesde muverture el gmtion des ressoums natumlles

biomass yields, high leaf area index and early ground covet, and long canopy duration (Akobundu et al. 1999, Hairiah et a l 1991). It is necessary to evaluate more accessions in order to increase the range of M m a that can tit into diverse fasroing systems. The objective of this study was to evaluate the ability of ten Mumna accessions to suppress speargas in the forest-savanna transition zone at Ibadan, Nigeria. Results from this experiment are important in their potential for reclaiming land that has been abandoned to speargmss.

Materials and methods An experiment was established on a farmer's field located near Ibadan (7915'N, 3O55' E), Nigeria, fiom 1997 to 1998. The soil type at the site was a sandy loam (Alfisol)

with pH 5.8, organic matter < 1%, and soil texture of 81% sand, 11% silt, and 8% clay. The site was located in the forest-savanna transition zone, which has an annual mean temperature of 26" C and an annual precipitation of 2250 mm. Tbe rainfall has a bimodal distribution with two major peaks in July and September. Prior to this study the experimental site was in fallow for 2 years and the fallow vegetation was dominated by speargrass. The experimental design was a randomized complete block with 10 treatments and 3 replications. Treatments were accessions of Muana: M. cochinchinensis, M u m a spp. Georgia, M m a spp. Ghana, Mucuna spp. Jaspeada, Mumna spp. Preta, M. pmriens vat. utifis (control), Mt(cuna spp. Rajada, Mtcctma spp. Vemcruz @lack seeded), Veracm (mottled seed), and Veracruz (white seeded). Seeds were free from pathogens as they were treated with 3% gastoxin. Seeds of Mumna were obtained Erom the Center for Information on Cover Crops in AfFica (CEPCA) based in Cotonou, BeniF. Plots were 10 m x 10 m. During the first week of June each year, the experimental site was slashed manually; shoots wete allowed to dry for one week and then b m t . Mucuna spp. were sown on 5 June 1997 and 21 June 1998 at a spacing of 100 cm (mtmow) and 25 cm (itmow) on the same plots in each year. The population was approximately 40 000 plmtsha. All plots were weeded manually 2 and 4 weeks after sowing (WAS) following recommendations by Versteeg and Koudokpon (1990). Emergence of M m n a accessions was evaluated Z WAS every year by counting emerged seedlings in ail the ten rows in each plot. Ground cover was assessed by the beaded string method ( S m t i n o 1991) from 4 to 32 WAS. Every year, M a m a biomass yield was assessed by harvesting plant material %om two 1-m2quadrats 16 WAS. Speargrass shoot and rhizome biomass yield was assessed from four 0.25 m2 quadrats per row fiom each plot. Each row was only harvested once during the entire study period Rhizomes were excavated to a depth of 25 cm. All plant material was oven-dried at 80"C for 48 h before determination of biomass yields. Canopy d ~ a t i ~ n

Cover crop benefitdBBn4fices des plantes de couverture 65

was derived from ground cover measurement and was defined as the time when Mucuna covered at least 40% of the ground.

Data were analyzed using the PROC MIXED procedure in SAS (Statistical Analysis Systems, SAS Institute, Cary, NC 275 12-8000). Means were separated using the standard error of the mean. Spearman's correlation was performed on Muczrna growth attributes and speargrass biomass to determine their relationship.

Results

Mucuna seedling density The seedling density of Mucuna 1 WAS is shown Table 1. In both years, the density of Muctlna seedlings was very low (< 50% of the targeted population). In 1997, germination percentages ranged from 15 to 31% for all accessions except M. cochinchinensis and Mucuna spp. Rajada, which had 44% of its seeds germinated and emerged. Thirty to 49% of the seeds germinated within 1 WAS in 1998. Volunteer seedlings may have increased the Mucuna seedling density in 1998 compared to 1997. Udensi et al. (1999) reported that when mature seed of Mucuna is not harvested volunteer seedlings became part of the plant community in subsequent years. Averaged over the 2 years of the study Mucuna spp. Ghana and Mucuna spp. Veracrur (black and mottled seed) had the lowest seedling density. M. cochinchinensis had the highest number of seedlings per ha in both years. Other accessions showed inconsistent stand development over the 2 years. Poor seedling emergence reported herc has also been reported in M. cochinchinensis, Mucuna spp. Georgia, Mucuna spp. Freta, Mucuna spp. Jaspeada, and Mucuna spp. Veracnrz-stephan (Qi et a!. 1999). Soaking seed in warm water has been suggested as a means to promote higher germination in hard seed such as Mucuna (Chee and Chiu 1997). Early germination offen gives an accession significant advantage over weeds that may last for the whole growing season. Poor performance of any accession at the end of the season may be due to poor germination or other reasons, for example, poor canopy development.

Canopy development Canopy development measured as percentage ground cover varied with accession (Table 2) and time of assessment (data not shown). In 1997 ground cover of more than 80% was achieved by Mucunapruriens var. urilis at 14 WAS and all other accessions by 10 to 12 WAS. The canopy of M. cochinchinensis, Mucuna spp. Georgia. Mucuna spp. Preta, Ad. pruriens, and Mucuna spp. Veracruz (black seeded) persisted (> 40% ground cover with green leaves) for more than 24 WAS after sowing in 1997. Other accessions shed their leaves earlier and mulch was still visible on the ground except in plots witb Mtlcltna spp. Ghana and Mucuno spp. Rajada where the mulch had

66 Cover crops br naturaj resource managemenfllantes de couverlrrnet gestian des ressources nahaelh

Table 1. Mucuna seedling density 1 week after sawing in 1997 and 1998. Seedling density (numberha) 1997

Accession

1998

Mean

Mucuna cochinchinensis Mucune spp. Georgia Mucuna spp, Ghana Mucuna spp. Jaspeada Mucune spp. Preta Mucuna pmriens var. utilis Mucuna spp. Rajada Mucuna spp. Veramz (black) Mucuna spp. Veracnrz (mottled) Mucuna spp. Veracruz (white) SE t*) Tabla 2. Percentage ground cover by gfeen leaves and rnutch 24 weeks after sowing in 1997 and 1998.

1998

1997

Accession

Canopy % green duration leaves % mulch (weeks)

Mucuna cachinchinensis Mucuna spp. Georgia Mucuna spp. Ghana Mucuna spp. Jaspeada Mucuna spp. Preta Mucona pnrriens var. utilis Mucuna spp. Rajada

96.7 66.7 10.0 16.7 66.7 53.3 0 Mucune spp. Veracrur (black) 53.3 Mucune spp. Veracrut (mottled) 26.7 Mucuna spp. Veracruz (white) 30.0 SE (2)

6.8

0 23.3 90.0 56.7 23.3 33.3 100.0 33.3 43.3 40.0 8.4

> 24 24 < 20 < 20 > 24 > 24 c20 > 24 c 20 e 20

% green leaves

Canopy duration % mulch (weeks)

100.0

3.3

753

36.7 90.0 80.0 33.3 46.7 100.0 46.7 73.3 70.0 7.1

5.9 43.4 84.8 60.4 5.2 73.6 58.2 58.0 10.8

> 24 > 24 c 20 < 20 > 24 > 24 < 20 > 24 c 20 < 20

completely disappeared. All Mucuna accessions completely covered the ground surface 8 to 10 WAS in 1998. With the exception of plots sown to Mucuna spp. Ghana and Mzrcuna spp. Rajada where the canopy senesced early (18-3 1 WAS), all the other accessions persisted beyond 3 1 WAS. In both years, M. cochinchinensis survived during the dry season and sprouted fiom the rootstock at the beginning of the following rainy season (1998 and 1999). The mulch of this accession and that of Muntna spp. Jaspeada did not disappear during the dry season. The long canopy duration of M. ~ochinchinensisand the mulch persistence particularly of Mumna.spp. jaspeada collectively contributed to the improved suppression of speargrass by these accessions. These results are supported by Akobundu et ai. (1999) who found that

Cover crup beneIfwB&Bfiees des ptantes de cnuverture 67

M u m accessions with longer canopy duration suppressed speargrass better than short seasoned accessions. They also rcporied that mulch left by the senesced M u m a canopy could suppress speatgrass dutiag the dry season.

Mucuna biamass yidds Biomass yields of Mvmuta are shown in Table 3. In 2997, U cochinchinensis and M v m a spp. Rajada had the -lowest biomass yields, which were similar to that .of Mucwna prwriens var. uiiiis, the control accession. The rest of ihe accessions had significantly higher biomass production than the control with Munrna spp. Preia and Maas1a spp. Jaspeada having the highest biomass production. In 2998, M. cocJzinchinensis and M u m a spp. Veracruz (white seeded) had higher biomass yields than the rest of the accessions while M.pwiew and M ~ m spp. o ICajada had the lowest biomass. Averaged over the 2 years of the study, M. cochinchinensis, Mwwna spp. Jaspeada, and Mumna spp. Veracruz (mottled and white seeded) were superior in biomass production than the rest of h e accessions. M.pmriens var. utilis and Mucuna spp. Rajada were the poorest biomass producers. The superiority of M. cochinchinerrris in biomass production has been previously reported (Akobundu et al. 2999, Carsky et al. 2998).

Spewgrass biomass yields (1998) At ihe beginning of the study in 2997, speaqpss biomass was similar across treatments with the mean being 445 @. Speargrass biomass was measured 2 year

after the initiation ofthe study because the suppressive effectsd Muctula occur over a long period of time. Generally, after 2 seasons of sowing cover crops, all Mucuna accessions reduced the biomass of speargtass when compared to the biomass in 1997. However, the extent of control differed with accession (Table 4). M.cochinchinensis, M u a m spp. Jaspeada, and M u m a spp. Veracruz (mottled and white seeded) had the largest impact on speargrass biomass, which was reduced by 79-96%. M u m a spp. Pceta and M u m a spp. Ghana reduced the biomass of speargrass to the same extent as the control (6248%) while plots sown to Mucuna spp. Rajada had the highest speargrass biomass. Mucuno biomass (r =4-63)and % p u n d cover (r = -0.69) were negatively correlated with speargrass biomass. Seedling density and speargrass showed a moderate level of correlation (r = -0.37).

Discussion and conclusions Wis study showed clear differences in seedling density, percent ground cover, and biomass of 20 accessions of Mucmm. Some of these growth attributes have been associated witti better competitive ability against weeds (Garrity et al. 1992, Wortm a q 1993). The high correlation between spewgas biomass and Mucuna biomass

68 Cover crops for naturalresourcemanagemenfllantesde rowerlure stgestion des ressaurces naturelles

Table 3. Mucuna biomass yields 16 weeks after sowing in 1997 and 1998. Biomass yield (kglha) Accession

1997

Mucuna cochinchinensis Mucuna spp. Georgia Mucuna spp. Ghana Mucuna spp. Jaspeada Mucuna spp. Preta Mucuna pmriens var, utilis Mucuna spp. Rajada Mucuna spp. Ve~acruz(black) Mucuna spp. Veracruz (mottled) Mucuna spp. Veracruz (white) SE (2)

2104 2540

461 5 2070

2411

2862

3325 2913

3698 2716 2144

1809

Mean

2182 3089

1986 2432 2491 2764

3526 4276

474

458

Table 4. Response of speargrass biomass to different Mucuna accessions 20weeks after sowing in 1998.

Accession Mucuna coch(ncbinensis Mucuna spp. Georgia Mucuna spp. Ghana Mucuna spp. Jaspeada Muduna spp. Preta Mucuna pruriens var. LltiIis Mucuna spp. Rajada Mucuna spp. Veracruz [black) Mucuna spp. Vetacruz (mottled) Mucuna spp. Veracrur (white)

Speargrassbiomass (gld)

% reduction

191

171

62 83

76 158

.I41 271 95 107 68

64 68 39 79 76 85

and percent ground cover indicates that accessions which were higher in these attributes suppressed speargrass better. M. cochinchinensis, Mztnina spp. Jaspeada, and Mumno spp. Veracruz (mottled and white seeded) had higher biomass production. They also covered the ground longer by maintaining their canopy or when the canopy senesced the mulch fiom these accessions persisted during the dry season. In M. cochinchinensis plots, we observed that in addition to the growth attributes mentioned its rootstocks had the ability to survive during the dry season which enable it to reestablish with the first rains. M. cochinchinensis has been reported ro develop an extensive root system that goes down 180-240 cm into the soil profile (Anonymous 1997). The ability of M. cochinchinensis to resist drought, diseases, and pests has been reported by Lin and Kuang (1991). In contrast, root development in M. pruriens var. zttiiis has been reported to be shallow (Nairiah et al. 1989). The moderate correlation between seedling density and speargrass biomass suggests that accessions that had

Cover crop benefi&Bfices des plant& de muverture 69

relatively higher seedling density (M. cochinchinensis) may have developed bigger canopies and covered the ground earlier thereby enhancing their competitive ability. Mucuna spp. Preta, Munula spp. Ghana,M. pvuriens var. utilis, and Muclrna spp. Rajada were the least effective in suppressing speargrass probably because these accessions had poorer seedling density, shorter growth cycles, and when their canopies senesced, they did not leave any mulch on the ground. Since this study was conducted in one location, we would recommend that other researchers, especially in areas where M. prrrriem var. utjlis does not grow well, conduct a similar study in their environments to identie a range of accessions which give the most effective weed control or other benefits. Studies to improve the emergence of M u m a are also recommended.

References Akobundu, LO., U.E. Udensi, and D. Chikoye. 1999. Mucunrr spp. suppresses speargrass (lmperata cylidica) and increases maize yield. International Journal of Pest Management (in press). Anonymous. 1997. Mucum cochicMwnsis:a potential short-term legume cover plant. Planters' Bulletin (Malaysia) 150: 78-82. Berner, D.K., AS. Killani, E. Aigbokhan, and D.C. Couper. 1992. MacrophominaphaseoEiM on tropical cover crop Mucum prurierrs var. d i s . Plant Disease 76: 1283. Carsky, R.J, S.A. Tarawali, M. Becker, D.Chikoye, G. Tian, and N. Sanginga 1998. M m m herbaceous cover legume with potential for multiple uses. Resource and Crop Management Research Monograph 25. IITA, Ibadan, Nigeria, 52 pp. Chee,-K.H. and S.B. Chiu. 1997. Viability test of leguminous cover crop seeds. Planter (Malaysia) 73: 581-582. Garrity, D.P., M. MovBIon, and K. Moody. 1992. Differential weed suppression ability in upland rice cultivars. Agronomy Journal 84: 58659 1. Garcity, D.P., M. Soekadi, M. Van Noordwijk, R. De La Cruz, P.S. Pathak, H.P.M. Gunasena, N. Van SO, G. Huijun, and N.M. Majid. 1997. The Zmperntn giasslands of tropical Asia: area, distribution, and typology. Agroforestry Systems 36: 1-29.

Wairiah, K. and M. Van Noordwijk. 1989. Root distribution of leguminous cover crops in the humid tropics and effects on a subsequent maize crop. Pages 157-169 in Nutrient management for food crop production in tropical farming systems, e d k d by Van der J. Heide. ~nstiktefor Soil Fertility, Haren, The Netherlands. Wairiah, K.. Van. M. Noordwijk, and S. Setijono. 1491. Tolerance to acid soil conditions of the velvetbean Mucmpruriens var. ufilis and M.deeringiana. I. Root development. Plant and Soil 134: 95-105.

Lin, M.Z. and W. S. Kuang. 1991. Study on the L-dopa content of Stizolobium germplasm resources in Guangxi. Crop Genetic Resources No, 19-20.

70 Covercmps for natural resomemanagemenWPIantes de couverttrmagestion Ues ressou~~es natureIles

Qi, A., R.H.Ellis, J.D.H.Keatinge, T.R Wheeler, S.A. Tarawali, and R.J. Summerfield. 1999. Differences in the effects of temperature and photoperiod in progress to flowering among diverse Mumnrs spp. journal of Agronomy and Crop Science 182: 249-258. Sanginga, N., B. ibewiro, P. Noungnandan, B. Vanlauwe, J. Okogun, 1.0. Akobundu, and M. Versteeg. 1996. Evaluation d symbiotic properties and nitrogen contribution of Mumna to maize in the derived savanna of West Africa Plant and Soil 179: 119-129. Sawantino, M. 1991. Methodologies for screening soil improving legumes. Rodale Institute Research Center, Kutztown. 312 pp. Udensi, E.U., 1.0.Akobundu, A.O. Ayeni, and D. Chikoye. 19-99, Management of cogongrass (lmperata cyfindricn) using velvetbean (Mucuna pmrietw vat: atifis) and herbicides. Weed Technology 13: 201-205. Vemeeg, M.N.,E Amadji, A. Eteka, A. Gogan, and V.Koudokpon. 1998. Fanners' adoptability of Mucuna fallowing and agroforestry technologies in the coastal savanna of Bmir. AgFiculm l Systems 56: 269-287. V d e e g , M.V. and V. Koudokpon. 1990. Muntna helps control Imperata in southern Benin West Africa Fanning SystemsResearch Network Bulletin 7: 7-8. Mssoh, P.V., V.M.Manyong, R.1. Carsky, P. Osei-Bonsu, and M. Galiba 1998. Green manure cover crop systems in West Africa: experiences with Mumna.Pages 1-32 in Cover crops in West Africa: canDibuting to sustainable agriculture, edited by D. Buckles, A. Eteka, 0. Qsiname, M.Galiba and G. Galiano. international Research Developement Center, Ortawa,

Canada Wilmot-Dear, C.M. 1992. A revision of Mucuna (Leguminosae: Phaseoleae) in Thailand, 'Indochina and the Malaysia Peninsula. Kew Bulletin 47: 203-245. Wortmann, C.S. 1993. Contribution of bean morphological characteristicsto weed suppression. Agronomy Journal 85: 840-843.

An approach for the evaluation of herbaceous legumes with multiple benefits S.A. Turmuaii It~~ernarrotial insr~rureof Tioprcal dgriculrure and Internano~talLtvesrock

Research Instr~ure,Ibadan. ?jigeria

Abstract In order to promote the identification of herbaceous legumes that may contribute to weed control, soil fertility, crop production, and livestock enterprises. as a means of encouraging sustainable agricultural practices amongst resource-poor farmers, an evaluation method using a simple sampling approach is described. To illustrate the method, results from one experiment in the derived savanna of Nigeria conducted over a period of 2.5 years are presented. The experiment included 14 accessions of single legume species, 9 mixtures of species, and 4 grain-legume accessions (soybean and cowpea). Mixtures of species, including combinations of rapidly establishing and slowly establishing but more persistent species, were designed to stabilize yield and minimize the risk involved in introducing herbaceous legumes. Although the biomass production of the mixtures was less than the best single species, they did remain stable over the evaluation period. Whilst the rapidly establishing species disappeared from the mixtures after the establishment year, the other components were able to compensate for this, and mixtures had relatively stable yields throughout the period. Grain legumes produced substantial biomass only during the establishment year, but have the potential to contribute to systems where farmers' circumstances permit the use of inputs. Such variations, together with those relating to speed of establishment, biomass production, and persistence over the evaluation period, are discussed with respect to the need to identify species or mixtures that are suitable for farmers' socioeconomic circumstances as well as biophysical conditions.

R&umQ Afin de promouvoir I'identification des ltgumineuses herbactes susceptibles de contribuer a la lutte contre les adventices, a la fertilitt du soh a la production des cultures et aux activitks de production animale, en vue d'encourager I'adoption de pratiques agricoles durables par les agriculteurs a faibles revenus, une mdthode d'tvaluation reposant sur une approche d'tchantillonnage simple est dCcrite ci-apres.

72 Cover crop for natural resoume managemenvplantes de mmmm st gestia, des ressourc~s namRes

Afin d'illustrer cette mkthode, des rksultats provenant d'une experiencemenke dans la savane ddrivde du Nigkria pendant 2.5 anndes sont prksentds. L'expdrienee a port6 sur 14 obtentions d'une seule espece de ldgumineuses, 9 m8mges de l6gumineuses et 4 obtentions de ltgumineuses A gtaines {soja et nikbd). Les rn&langesde Itgumineuses, comprenant des esptces dtablissement rapide et des especes 8 dtablissementlent mais plus persistantes, ont dtt tlaborks afin de stabiliser les rendements et de rdduire les risques relatifs i l'introduction des ldgumineuses herbacks. MEme si la production de biomasse des melanges etait plus faible que celle de la meilleure espece unique, etles sont demeurkes stables pendant la pdriode d'bvaluation. Tandis que k s espkes B ttablissement rapide ont dispm des mkianges aprks l ' m t e d'&.ab!issement, les autres composantes ont pu compenser cene disparition et les mblanges ont eu des rendements relativement stables pendant la pdriode. Les Iegumineuses A graines ont produit une biomasse substantielle seulement pendant I'annte d'itablissement, mais elles ont present6 un potentiel de contribution aux systemes oli les conditions des agriculteurs permettent l'utilisation des haants. Ces variations ainsi que celles IiCes B la rapidit6 de I't5tablissemeng a la production de biomasse et h la persistance pendant la ptriode d'tvaluation, font I'objet d'une discussion par rapport au besoin &identifier les especes ou les melanges qui sont adaptes aussi bien aux conditions socio-Cconomiques des agriculteurs qu'awc conditions biophysiques.

Introduction Given current scenarios of increasing human (Badiane and Delgado 1995) and livestock populations (Winrock 1992, Delgado et al. 1999), forcing agricultural intensification and placing immense demands on the natural resource base {de Haan et al. 19971, herbaceous legumes are recognized to have potential to contributeto alleviating some of the stresses faced by farmers. For many decades, the use of leguminous cover crops, notably Mucuna, has been advocated as a means of weed control (Akobmdu and Udensi 1995) and improving soil fertility (Sanginga et al. 1996, Buckles a al. 1998, Carsky et al. 1998). Forage legumes, such as Sty!osantkes species in West Africa (MohamedBaleem and Suleiman 1986, ikwuegbu et a1.1996), Australia, soutfieast Asia, and South America (Stace and Edye 1984, de Leeuw et al. 1994), and Centroserna species in South America (Schulw-Kraft et a!. 1991) are recommended as livestock fodder in tropical regions, especially where there is a pronounced dry season. More recently, it has become apparent that herbaceous legumes with multiple benefits are likely to be more acceptable to fanners in mixed crop-livestock systems, notably those which provide some grain for human consumption as well as improying soil fertility andor providing livestock fodder {Tarawali and Mohamed-Saleem 1995, Tarawali and Peters 1996, Weber 1396).

Cover crop benefitskl~nefices des plantes de couverlure 73

Despite the obvious benefits of introducing herbaceous legumes, adoption by farmers is often low (Thomas and Sumberg 19951, although even relatively modest rates of adoption in West Africa, have given substantial internal rates of return (Elbasha et al. 1999). Amongst the contributory factors resulting in limited adoption, lack of available gennplasm is ofien cited as a reason (Elbasha et al. 1999, Tarawali et al. 1999a). This is apparent if, for example, the use of Sfylosanthes for dry-season pastures (fodder banks) in West Africa is considered. For over a decade from the early 1980s- the use of fodder banks was promoted, but relied entirely on one cuttivar of Stylosanlhes, S.harnata cv. Verano (Tarawali 1991). The availability of alternate varieties, which could better address the different needs of farmers, and variations in agroecology, was limited. A similar scenario could be related for cover crops in West Africa, where Mucuna puuriens var. utilis has been almost exclusively recommended. In some respects, citing a lack of gemplasm could be considered paradoxical--the International Livestock Research Institute has over 8000 accessions of herbaceous legumes in its genebank in Addis Ababa, Ethiopia, whilst the Centro lnternacional de Agicultura Tropical (CIAT) in Cali, Colombia, has in excess of 18 000 accessions (Maass et al. 1997). it is therefore apparent that appropriate approaches to the selection of material from these collections and subsequent evaluation and recommendation need to be developed. In the present paper, one such approach to the evaluation of a number of herbaceous legume accessions is described, using the results from one experimental site as an example. The methodology used is essentially as described by Tarawali et al. (1995). Species selected for these trials were chosen based on previous knowledge of their performance in similar environments(Tarawali et al. 1999b,and references therein). in this instance, however, there were additional treatments in the form of mixed-species plots and gain-legume plots. The latter were included so as to allow comparison of the grain and fodder yields of both a grain type and fodder type each of soybean (Giycine mux) and cowpea (Vigna unguicuiata). Mixed plots were designed to maximize the benefits of different species (Peters et al. 1999). Each mixed plot consisted of three different species-component one, with fat, early establishment but little persistence (Centrosema pmcuorum, Mucuna pruuiens, or Lablab purpureus), component two with slower establishment but persistence to subsequent seasons (Aescbymmene hisrrix, StyIosanrhes guianenris ILRI 164, or S.harnrrta ILRI 75). and component 3 with the ability to remain green in the dry season (Centrosen~ab r m i h u m ) . It was anticipated that such mixed plots would be more robust in terms of variations in microclirnate and management and would therefo~stand a better chance of producing agood legume stand whereas a sole plot of any one of the species could fail, depending on the pressures. It was also anticipated that the composition of such mixed plots would change throughout the trial period.

Cover crops for nahrral resoune managemerW1anfesde rnuvertwe etgeSio~des ressourcss n a m l l s

Materials and methods Trial es#abIishment The trial was established in June 1997 on the research f a m of the International Livestock Research Institute (ILRi) at Fashola in Oyo State, southwestern Nigeria (7'54' N, 3O46' E; 270 rn above sea Tevel) in the derived savanna. At the start of the experiment, a bulked soil sample from the trial site indicated that the soil had pH 6.6 (HSO), nitrogen 0.067% (Kjeldabl), phosphorus 3.4 mgtkg (Bray I), and organic carbon 0.75%. Rainfall is usually bimodal, be@ig in March and ending in October, with a short, and not always discrete, dry season in July or August. Rainill in 1997 totalled 1367 mm in 1997,977 mm in 2998, and 2386 mm (up to 18/10/99) in 1999. The trial layout was a randomized complete block design with three replicates. Each plot was 2.5 m x 5.0 m, with the central 1.0 n x 4.0 in being used for samplimg. Each plot had four rows of 5 m length, evenly spaced with 0.5 m between rows. The plant material used for the experiment is listed in Table 1. All seeds were from batches that had been multiplied locally by iITA. In the mixed-species plots, sowing rates for each of the three components were adjusted to one-tRird of the normal rate, which was used in the corresponding single species plots. All seed, except those of the grain legumes, were scarified using sandpaper before sowing (Tarawali et al. 1995) and small seeds were mixed with dry sand to enable even dispersal along the rows. For the mixture plots, the seeds of the three components were mixed together before sowing.

Data coltection~~b1ishment phase Germination (based on the number of emerged seedlings in one 1 mSquadrat randomly placed within the central sampling area) and soil cover (estimated as 0,2,5,10,25,50, 75, or 100% in the same quadrat) were assessed 4,8, and 12 weeks after planting. Flowering was monitored in 1991during the estabiishment phase, up to the time of below) and assessed as the first harvest (standardization cut for the dry season-ee days after planting until 50% of the plot had flowers. This is based on a visual assessment of the entire piot and therefore does not require that single plants be distinguished as this is difficult for twining species.

Data collection-productivity and quality In order to assess productivity and herbage quality, a dry-season and a wet-season period were assessed, each for 2 years (i.e., dry season 1997/98 and 1998/99; wet season 1998; wet season 1999). Each period of assessment commenced with a standardization cut, when all plots were cut down to 15 cm above she soil sui-Face. At the same time, two 1 mZquadratswere harvested (also 15 cm above soil surface) from

Cover crop benelits#dn&tices des pjantes de muveriure 75

76 Cover cmm i'or natural resournmanagementlPantesde wwerture el geslion des ressources namltes

the central sampling area for productivity and quality assessment. The &esh weight of the harvested quadrat was measured, then a subsample of 200-300 g k s h weight weighed and oven dried at 60째C to a constant weight to determine dry matter. Dry samples &omthe wet- and dry-season harvests in 1998(onset of the wet season, end of the wet season, and 6 weeks into the dry season) were ground through a 1 mm sieve and analyzed for nitrogen content (Micro-Kjeldahl) which was subsequently converted to crude protein by multiplying by 6.23. The dry-season assessment period commenced once the rain had ceased. Six weeks after the standardization cut, half of the plot was cut again, with one lm2 quadrat assessed as above. Six weeks h e r (i.e., 12weeks after the standardization cut) the plot was harvested again, with one 1 rn2quadrat assessed &om both the part cut after 6 weeks (referred to as 6 (2) weeks) and the part not cut since the standardization cut. At each dry-season harvest, an estimate of the drought tolerance was made by estimating the percentage of the biomass in the assessed quadrats that was green. In 1998, the last cut of the wet season harvesting served as the standardization cut for the dry season. The wet-season assessment commenced in early June, when the rains were steady. Tbe central sampling area was divided into four 1 mZparts which were cut 3,6,9, and 12 weeks after the standardization cut. At each harvest, material was assessed as described above. At each evaluation time, any disease or pest incidence was also noted. Results were analyzed using the MIXED method of SAS (Little et al. 1996) as follows: proc mixed method = reml class replication accession model yield = accession random replication The accessions included both the total mixture yields and the yields of the individual components of the mixtures. Results are presented as means of the three replications unless otherwise stated.

Results Establishment period 1997 With the exception of Arachis pinfoi, which did not establish at all, and is therefore excluded from all analyses, all the legumes established, although for some species, emergence was poor. Differences between the seedling coun& and gemination percentages were highly significant [P < 0.0001). Estimates of germination percentages are shown in Table 2. There was lhle change in the numbers of seedlings counted 8 and 12 weeks a& planting. Mucunoprut-iens and Vigna unguic~fata (fodder) were the only accessionsto

Cover crop benefits/Bn8iices des plartfes ds auverlure 77

have germination percentages of 100%. The Cen!rosemaspecies all had germination percentages of around 50%, although in some of the mixture plots, Cenirosema brasilitrnum exceeded 70%. Germination of Aeschynomene hisfrir was variable and poor, except for mixture 5 where it exceeded 70%. With the exception of mixture 1, germination of Aescbynomene histrin was higher in mixtures. Chamaecrism rotundifolr'a also had very poor germination of only 3%. Srylosantl~esharnata iLRI 75 also had poor germination, especially in mixtures 5 and 6 where it was below 10%. Figure 1 shows the soil-cover estimates 4,8, and 12 weeks after planting. At each measurement time there were significant differences between the accessions (P < 0.0001). Four weeks after planting, the cover was less than 50% for all plots, although the two Kgna unguicuiata accessions both had the highest cover with over 45%. Only four other treatments had soil cover in excess oi"20% at this time: Labiabpurpureus, 124ucunapruriem,mixture 4, and mixture 9. All mixtures exceeded 10% cover, whilst eight of the sole species had less than 10% soi1 cover at this time. Eight weeks after planting, differences in soil cover were more marked. Seven treatments had cover of 50% or more, with Labiab purbureus, Mucuna pruriens (over 80%), Mgna unguicuiata (fodder) plus mixture 9 having over 70Y0 soil cover. Four accessions (Aeschyvromene hisinjc, Cha~?~aecrisra rotandfoiia, Stylosanthes hamara 1.75, and Sryiosanthes capitata) had soil cover less than 20%. Of the mixtures, with the 50% or more of exception of mixtures 1,3, and 5 (those with Centrose~napascuorm), the soil cover was contributed by component one (Labial, purpureus or Mucutza pruriens). Twelve weeks after planting, 12 treatments had over 70% soil cover, with four of these (Labiab purpureus, Mucuna pruriens, Vigna unguiculata (fodder), and mixture 7)exceeding 90%. With the exception of mixtures 1,3, and 5, all the mixtures had soil cover in excess of 70%, with again, component one making up 50% or more of this cover. In the period between the 8 and 12 week assessments, Centrosema brasilianum and Clitoria ternatea increased the soil cover dramatically, with less than 40% cover at 8 weeks to over 70% by 12 weeks. In contrast, Labiab parpureus, Mucuna pruriens, and figt~aunguiculata (fodder) had almost reached maximum cover by 8 weeks, and there was less than 15% change between these last two measurement periods. The earliest flowering accessions were Chanlaecrisfarolundgolia, CIitoria ternatea, and Vigna zinguicufaia (g), Labfab purpureus, Pueraria phaseoloides, and Cen!rosernapubescensdid not flower before the first harvest at 166 days after planting (Table 2). Observations of adjacent seed multiplication plots of thz same species indicated that all three flowered at around 180 days after planting.

Dry season At the onset of the 1997198 dry season (Figure 2), five accessions had yields of 10 ilha or more (Aeschynonzene histrir. Sryiosanrhes guianrnsis ( 2 accessions) and

ILRI 12463 ILR1 155 lLRl9857 ILRI 152 ILRI 10918 lLRl7621 l l R l 147 Utllis

A.histrix C. brasilionum C. pascuorum C. pubescens C. rotundifolia C. tematea L. purpureus M. prurlens ?I phaseololdes S. guianensis S. gulanensis S. hamafa S. hamata S. capitato V. unglliculala V. unguiculafa G. max G. max

---

2 61 55

-100 -

24 55

---

100 -

---

38 77

100 -

--46 --

34 75

---

46 -

72 72

% germination in slngle species and mixtures (where applicable) 4 weeks after sowlng Sole Mlx 1 Mix 2 Mix 3 Mix 4 Mlx 5 Mix 6 MIX7 Mix 8 Mix 9

19 57 56 51 3 50 55 100 43 lLRl 164 56 llRl15557 44 ILRI 75 16 ILRI 15876 28 ILRI 9052 21 1T86D-719 75 Tvu 12349 100 TGX 1645-2Be 73 TGX 1448-2E 77

Accesslon

Species

122 46 62 51

66 83

47 44 + I 66 131 ,+I 66 130 157

127 121 104 + I 66

DAP to 50% flower

Table 2. EsUmated mean germlnation percentages, based on number of seeds sown (Tabla I ) and seedlings counted 4 weeks after sowing. DAP to 50% flowering lndlca!es the days after planling to reach 50% of the plot with flowers; 4 6 6 lndlcates that flowering did not reach 50% before the first hki~estwhich took place 166 days after planting.

Cover cmp bsnelits/B8n8iicesdes plantes de crluveriure 79

Figure 1. Soil cover (mean % cover of 1 d quadrat) 4.8. and 12 weeks after planting. 1997 wet season. Mix 1 = C. pasdA. hisVC. bm; Mix 2 = M. p d A . h i m . &bra; Mix 3 = C.p a d s . gum. bra; Mix 4 = M.pru1.S. gNC. bra; Mix 5 = 5 C. pa&. ham/C. bra; Mix 6 = M. pru/S. ham/C.bra; Mix 7 = L pur/A. hisK. bm; Mix 8 = L pur/S. g u m . bm; Mix 9 = L purl... ham/C. bra For mixture plots: Component 1 0 Component 2 IComponent 3

Cmrcmps for nnafural resourcemanagemenl/Pantes de couverture el gestion des ressources naturefles

Stylosanfheshamafa(2 accessions)). All other accessions yielded less than 6 f i a , with mixture 3 having over 5 tha, although this was mostly made up 03 S@fosanthes gttianensis. Yields of the component species in the mixtures were much laver than the yields of the same species on compatible the single species plots. Six weeks into the dry season, yields were considerably lower, with only Cenrrosema pitbeseem reaching 1 tha. Cenirosema paswontm, Muctrna pruriem, Ggna unguicuiata (grain type), G. mux (2 accessions), and mixture 4 did not produce any biomass during this period. Cenfrosemabrasiiiunum was the dominant species in all the mixtures, although the yield for the single species was considerably higher (about double). When these areas were cut again after another 6 weeks, yields were all less than 500 kg/ha. SpIosanlhes pianensis (2 accessions) had the hiaest yields (400-450 kglha). Aeschynomene hisirk, Cenirosema pascuorzcm, Chamaemisfo rotundgoIia, Labfabpzrrpuretcs, Mz#c~ma prrrriens, Vigna zmnpiculara ( 2 accessions), Giycine max (2 accessions), and mixture 4 produced no biomass at all during this second 6-week period AAer 12 weeks of the dry season, only Centrosema brasilianzlm, S~fosanfkes pianensis (2 accessions), and mixtures 3 and 8 yielded more than 800 k@a. Mixture 6 had a surprising yield of Mucuna pruriepls, probably regrown from dmpped seed, which had disappeared from all other mixtures and single species plots. With the exception of this mixture, all other mixtures were dominated by Centrosema brasilianum. For all the single species, except Lablabp~rpurezrs,total yields when cut after 6 weeks and then again 6 weeks later were greater than for the single cut at 12 weeks (comparing the lower two graphs in Fig. 2). In contrast, yields of the mixtures were lower when cut twice. At the onset of the 1997198 dry season, estimates of % greenness ranged from 5 to 20% for the two grain legumes (Gt'ycine m w (g) and Vigno unpimlarn (g)) to over 90% for all the Centrusema and Stytmanrhes accessions. Twelve weeks after the standardization cut, when several accessions had already disappeared, greenness estimates ranged from 5% for Chamaecrisfarofundgo/icrto 50% for Splosanthes gaianensis lLR1 15557. In the second dry season (1998199, Fig. 3), 6 weeks after the standardization cut, S@iosanthesguiunensis (2 accessions), SdyEosanrhes hamafaILRI 15876, and mixture 8 had yields over 12 m a and these yields were all higher than for this harvest the previous year. Amongst the mixtures, all yielded similar or higher yields than the previous year. When these areas were cut again after 6 weeks, only the b ~ o Sfyi~santkespianensis accessions yielded less than the previous year, with all others having similar or higher yields. Highest yields of over 500 kg/ha were for Egna tcnguiculara (fodder) and mixture 9. Twelve weeks after the standardization cut, the two Styiosanthes pianensis accessions and mixture 3 yielded over 600 kgtha, but

189 160 140 120

1w 80 50

20 O M

~ p r

w Cm

w 6!4

w wuvf sbrnscp

uY.

~ * r

k s

-3

&bz

us.

-9

YII

40 30

20 I0

Biomass drj maLt yield

tvw

12weeks 120 1M

80 60 40

20 0

200 9Mf 128 81)

40 - C p l CDr

cs4

wL.u +u C*. bP*W

w -1

v a t

h l W

-0

YII -2

~ i l 5

'ha

Figurcr 2. Dry matter biomassyields [mean kg/haL 97198 dry season. Key for mixture plots as for Figure 3. The lower figure represents the total yields 05 the two harvest from the same part of the plot consisfing of the 6 weeks ( ) and 6 (2)weeks ( ) harvests.

82 Cover cmps far natural resoum&~ management/Plantesde cowetium el gestion des rassOvIces natmI1~s

180

im 140 120

60 40 20 0

60 50 40

30 20 10

~iomass dry

'"mCa CP M k L P l l y . p * w S p 4 -

shn

w m t

vug

bnxr

n 1

-9

asma m i ma

mam7

matter

yield (kglhal

12 weeks lur 1W 60

60 4G

20 0

6 * 6 weeks

-CP*

wChLPw

ms*m---V=T'

"--D I l p

n z

-4

Figure 3. Dry matter biomass yields (mean kgka). 197/98 dry season.Key as far Figures 1 and 2.

Cover crop benetiisBen6fi~des plates de couverture 83

these were still lower than the previous year, when these same three again had the highest yields, with over 800 k m a . Comparing the areas allowed to grow for 12 weeks with those cut twice (at 6 weeks and again after another 6 weeks), yields were similar or higher for the latter-notably the two Sguianensis accessions, which had the highest yields in both cases-although, for those cut twice, yields were more than double those cut only at 12 weeks. The pattern for remaining green into the dry season was similar to that recorded in ?he previous dry season, with Chamaecrista rofundifooliiahaving the lowest yield and accessions of Centrosema bvnsilianum and Stylosanthes pianensis h e highest. Wt season At the onset of the 1998 wet season (Fig. 4), seven accessions had not persisted at d l (CentrosemapizscIcoyum, Labiab parpureus, M m n a pruriem, Kgna unguiculata (2 accessions), and Glycine m m (2 accessions)). The highest biomass yield was for S~!oscmtheshamata ILRI 15876 (4.4 &a). Five other accessions had yields over 2 i h whereas all the mixtures yielded less than 2 h a It is notable that the composition of the mixtures had changed ikom 1997, when they were dominated by the annual species (component 1- C. parnonun, L.purpw-eus or M pwiem---see Fig. 1) to the more persistent components 2 andlor 3. For the subsequent harvests through the wet season, biomass yields were never as high as this frst cut. At the 3week harvest, mixtures 2 and 3 had the highest yields, although for subsequent harvests these were surpassed by single species' yields. At the 12-week harvest, the yields of Centrosema b r a s i h m in mixtures 1,2, and 4 were greater than the single species' yields of this species. Clitoria CerndeQ, Styiosanthes grcianemis, and Styiosanthes lramata accessions were the best yielding. The foddertype !I wguinrlata also gave a good yield in the 22-week harvest. At fhe onset of tbe second wet season in 1999 (Fig. 5), Stylosanthes pimemis LRI 164 had an outstanding yield of over 6 tma Five other accessions (Styosanfhes pionem& LRI 15557, Sty~osantheshamata &RI 15876, and mixtures 3,4, and 8 yielded 3 tlha or more.Seven accessions (Cenh.osemapasc~(orrcm, Labiab purpuetcs, M~cunapwiem,ngna ungsrimiata (2 accessions), and Glyciipe mar (2 accessions)) had disappeared completely and did not produce any further biomass. In the mixtures, Centrosema Irrariiirmum dominated mixtures 1, 2, and 7 where the Aeschynomene his&& component had disappeared, and the yields were similarto the sole Centrosema brusihum. Other mixtures consisted of Centrosema brasioliianum and component 2 (Stylosanthes pianensis or Stylosank hamnta), except for mixture 6, which was mostly Stylosrmthes hamafawith a very small amount of Mvmntzpmriens. Yields of component 2 in the mixtures were lower than the single species plots of the same species. As in the previous wet season, biomass yields for the remaining harvests

84 CPver aops for nafuiaIresouffie managementlPlanfesde muverture el gestion cles ressoum natrrrelles

Omet af wet season

m m 4w 300 mD 100

; 5D

30 20 10 0

1m Biomass dry mattor Vie'd

Coal

6weeks

1m j40

w 40

20 0

12 week

C4-CP4Cpic--~l"pp'~~=s;.SrrmT~v-',I.

~ r a l mr *a On@ I L t

19.) U*

Figure 4. Dry matter biomass yields (mean kgha). 1998wet season. Key for mixture plots as far Figure 1.

Covercrop b&neCWB&6Cces des planfes de couverture

ONet of wQLseasan 7M 6m

5m 4m

m 2M Iw 0

0 $0

a SD

211 70

6 weeks

180

dry

mauer ytd

120 :1

: 20

9 weeks 340

im 1M LYI CIO U)

20 0

911Q

m 1s 1M 50 0 LH

fL.

LC U

r* W

-1

.Ull

w r

a-". ( 1 -

U S

Cu*

I., I .

YI_,"kI

Figure 5. Dry matter biomass yields (mean kgiha). 1999 wet mason. Key for mixture plots as for Figure 1.

86 Covernops for natural resome managemenP/Pantesde rnmrlure et gesfion des resources natureiles

during the wet season were less than the first. At the onset of the wet season, yields of all the mixtures were the same or higher than at the same time in 1998. The higher yields were maintained for harvests at 3 and 6 weeks, but then declined such that by the end of the harvest period, only mixture 5 had a higher yield than in 2998. A similar pattern could be observed for the single species, where yields early on in the harvest period were higher in 1999, but were, with the exception of Aescttynomene kistrh, Centrosemapibescens, Paeraria phaseoloides, and Siylosanthes capitafa, lower than in 2998 by the end of the harvest period when only the latter two, plus mixture 5 yielded 2 t h a or more.

Disease and pest incidence There were no severe attacks of any diseases or pests throughout the trial period. At times of peak humidity, some incidence of anthracnose (Coletotricum spp.) was noted on tbe S(v1ascmthes species and Chamaecrista rofzindifoiia with, at the same time, foliar blight (Rhizoctonia spp.) and leaf spot (Cercospora spp.) on the Centrosema bmilimum and,to a lesser extent, Cennosemapubescens. Incidences of disease did not rise above 10%.

Cnrde protein Selected m d e protein values of the species contained in the mixtures for the wet and dry peFiods during 1998 are presented in Table 3. In general, values at the end of the wet season were highest in all cases. For Aesc@nomene histrix, except for mixture 1 at the end of the wet season, all crude proteh contents for mixtures were lower or similar to those for the single species. in h e case of Cenwema brasilianum at the onset of the wet season and 6 weeks into the dry season, m d e protein contents for mixtures were similar or higher &an those for the single species. At the end of the wet season, values for mixtures were lower or similar to that for the single species. For Svlmmthes gaianemis ILRl 164, m d e protein contents for mktum were similar or higher than those for single species, except for mixture 3 at the end of the wet season. Siylosanthes hamata ILEU 75 in mixtures had higher crude protein values at the end of the wet season than the sole species, but at other times sole legumes had higher values. For other accessions (data not shown), a simdar pattern was observed, with highest crude protein values at the end of the wet season. W~ththe exception of Siyiosanthes hamata ILRT 15876 at the onset of the wet season (9.5%), all crude protein contents were above lo%,with Cemsemapubescens having the highest value of 19.2% at the end of the wet season.

Cover crop beneZM9BnBfioesdes plant= da wrrvertum 87

Table 3. Selected crude protein values (mean % of dry matter) for the wat and dry periods during 2998. Sole refers to the value for the species in singte species as opposed to mixture plots. indicates that the species was no longer present, even though it was originally sown there.

Period

Onset of wet season

End of wet season

Treatment

Mix 1 Mix 2 Mix 3 Mix 4 Mix 5 Mix 6 Mix 7 Mix 8 Mi 9 Sole

Mix 1 Mi 2 Mix 3 Mix 4 Mi5 Mi6 Mi7 Mix 8 Mix 9 Sole

Siweeks into dry season

Mx i 1

Mh2

A. his

14.1

13.2 18.6 14.0

12.2 15.1 11.2 13.8 12.7 14.2 13.5 12.6 13.8 12.8 16.5 19.0 15.6 15.6 17.7 17.0

16.9

18.9

16.9

14.7 14.8 17.0

13.7 12.9

Mix 3 Mix 4 Mi5 Mix 6 Miu 7 Mix 8 Mix 9 Sole

C. bra

14.4

16.5

11.6 11.9 13.2 13.6 13.4 12.6 13.0 11.3 14.6 11.7

S. gui

S. ham

12.9 18.4 12.1

13.5 12.3

12.3

13.9 18.3 18.3 18.8

19.9 16.1

15.7 14.9

13.7 14.1 14.7 14.8 15.6 12.0

15.9 16.6

Discussion This simple experimental approach has provided considerable information on the performance and potential of a number of herbaceous legume species, which can be utilized to identify which legumes may be appropriate according to fhmers' requirements and agroecology. In this discussion, in addition to consideringthe results per se, the value of the approach used, and its limitations, together with suggestions for modification according to specific requirements are presented. Some discussion on the value and potential use of mixtures of legume species is also included. Species such as Mvcrtna pruriens and tablab purpureus were fast to establish, but did not persist after the first growing season; these would be potentially suitable where

88 Covercmps for natural resume managementlPanfes de cumerhre a?gesrion des m s o u m natmnes

fallow periods are very short and where weed control (and hence rapid soil cover) is important. Centmema pascuomm, usually recognized as a rapidly establishing species (Peterset al. 1994, 'krawali 1994a) did not perform well in the present trial. Its value is likely to be found h less humid environments where it has the ability to produce considerable biomass in short growing seasons (Tmwali 1994b). The porn performance of Centrosema pascuorum is evident in the mixtures as well, where mixtures 1, 3, and 5, which contained this species had the slowest establishment. Nevertheless, the other species in these mixhues (except mixture 5 where Stylosmthes hamata had very poor gemination) were quick to compensate for this (see Fig. 2 for example). Indeed, over the whole evaluation period, mixture 3 (Centrosema pascuomdStyIosanthes guianensis/Centrosema brasiliamum) seems to be one of the most stable combinations. Mixtures with Mtrcuna prtrriens or Lablab pwpureus, whilst fast to establish, were so dominated by these components initially, that it was some time before the other two components, which provided the legume component after the establishment year, could get property established. Amongst the other accessions, the performances were generally compatible with other studies in the region (see, for example, Tarawali et al. 199% and refmnces therein). Araehis pintoi, whilst successful in tropical South America, has failed completely in this environment in o b r satdies (Peters et al. 1999) due to poor gemination and predation by rodents and birds.S~Eosanthesaccessions, especially SlyIosanthes pianensis performed well throughout the evaluation period and were able to grow in both wet and dry seasons. Stylosanthes guimensis LLM 164 contributed well in mixtureplots, especially after the redudon of component one (see above). SqImmtk harnata accessions generaily grew better in the wet season and the contribution of Stydosantheshamata ILRl75 in the mixtureplots was less than the Stylosarrthes guinnensL ILRT 164. The performances of the rwo accessions of each of these species varied such that overall, there was little difference between them. Sfylosanfhes capitata generally performed poorly, except for the h l hasvest at the end of the 1999wet season when it had the highest yield. Although not measured in the present experiment, this may be related to its poor noddation, which has been observed to improve &er several years' growth on the same site Farawali and Peters 1997). Aeschynomene his@& and Chmnaecrisfa rotundifolia generally did not perform well, although it has been shown they are suitable fbr less humid environments (e.g., Tarawali 2994a). Centrosema brasiliamm and Centrosema pubescens had reasonable yields throughout, both growing well and remaining green during the dry season. Cen&osernabrasilianum provided a stable component in all the mixture plots. CIitoria ternatea and Pueraria phaseoloides were not outstandig, but were not amongst the worst either in terns of persistence and biomass production.

Cover crqp benefiW8BnBEces des plants de wuverfum 89

In terms of biomass yield, the grain legumes performed well only during the establishment period. However, it is the multipurpose nature of these species, which can provide grain for human food and fodder for livestock as well as contributing to soil fertility that is of particular interest. Biomass yields of the cowpea accessions were similar to those reported by Tatawali et al. (1997) in the same environment, where IT86D-7 19 (pin type) produced 1.75 t h a fodder and 250 kglha grain and Tvu 12349 (fodder type) produced about 2 tflza fodder and no grain. For farmers whose circumstances permit if and who are interested in grain production, the use of insecticide spray would enhance cowpea grain yield, but may reduce the fodder component. Similarly, for soybean, fodder yields tend to be Iow, and consist mainly of the dry stalks and pod walls after grain threshing, but the plant can produce grain for consumption or sale, and improve soil fer&ility.Such species would appeal to f m e r s who have good market access for grain sales and do not emphasize livestock production. These examples stress the importance oftargeting the introduction and use of legume species according to, not only the biophysical conditions, but also farmers' socioeconomic circumsmces, Inthe present experhent, it could be argued that considerable emphasis has been placed on biomass yields, without considering other aspects of the legume performance that would be important in assessing their potential. Because of the cutting intensity imposed in the present trial, flowering was only monitored during the establishment period, and seed production could not be accuratek monitored These are important criteria for determining how species may fit into different h-mimg patterns (Qi et al. 1999) as well as the potential for easy diffusion (ie., if seeds are readily available). The simple addition of a single row of each species for the assessment of these parameters as suggested by T k w a l i et al. (1995) could easily enable this. h this particular case, adjacent seed multiplication plots of the same species were available to provide this information (data not shown). The effect of the different legume and species combinations on soil fertility and subsequent crop production are also important considerations(Tatawali and Peters 1996)and the most appropriate approach would be to plant a cereal crop on the plots aRer an appropriate evaluation period (Tarawali 1994a). In the present experhen&the aim was to gain a comprehensive understanding of the behavior ofthe species aad combinations over a 2.5-year period. However, in some chmstances, where some information is already available on species performance, and it is known that fallow periods in excess of one year would not be feasible, cropping could be introduced earlier (see for example, MulY et al. 1998). In many instances, the use of legume cover crops is advocated as a m m s of weed control, b a this was not assessed in the present experiment. Peters et al. (1999) conducted a similar experiment at the same location in which weeds were not controlled after the establishment period and in which the trial was periodically grazed

90 Cwer crops f o r m a l ri?soufce managemenPlantes de wmtfure et gestion des ressources naturelles

by cattle. Modification of the experimental approach to include aspects such as this would be possible, and could be designed with specific fanner situations in mind. For example, from the information in the present trial alone, it may be concluded that Aeschynomene his- may not have my outstanding value. However, in other experiments in the northern Guinea savanna, it has been shown that this species has the potential, in addition to providing fodder and improving soil fertility, to reduce the soil seedbank of the parasitic weed Striga hermonrhica (Weber et al. 1995, Merkel 1996). Such a properly with readily visible results should not be overlooked as it could provide an important 'Slrindow of opportunity" for the introduction of legume species to farmers. The data collected from the present trial would be suitable for use for modelling approaches, if combined with appropriate soil and climate information. it is well known that mixtures of crops are common in farmers' fields and are part o f a risk avoidance strategy (Peters et al. 1999, Tarawali et al. 1999b) as well as an approach to make maximum use of the resources during the growing period. Rattunde et al. (1988) report a similar approach using mixtures of groundnut cultivars with difFerent growth habits and maturities to try and maximize resource utilization and minimize risk. As in the present study, the mixtures did not produce maximum yields, but they did present very stable yields. This is an important consideration when considering the range of microenvironment and management variations that may be presented in on-f8rm situations. Through introducing a robust mixture of species, it is much more likely that at least some components of the mixture will succeed and that h e r s will not be disappointed or disillusioned through the failure that could happen with single species stands. A&en et al. (1991) report a series of grazing experiments ushg mixtures of legme species oversom into grass pastures in Florida. The strategy employed was similar to the one reported ia the present article, where a fast growing species was combined with slower establishing ones to give a stable pasture over a number of years. Again, as with component 1 h the mixtures, the fast growing species disappeared after the establishment year, but the legume componentwas subsequently made up of the other species..Mixtures of legume species, with their feamres of longterm stability are likely to be more suitable for situations where fallow periods of one year or longer are available and where the legumes are likely to be used as fodder (grazed or cut). Reategui et al. (1995) also used multiple legume species for pastme establishment and stressed that a combination. of species differing in speed of establishment and persistence would be appropriate for long-term p-es. In cases where only a short period is available in the cropping cycle for legume growth, the rapid gro* and ground cover of species such as Mamna pmiens and LabEab purptcreus wodd be appropriate, but again, as a risk avoidance strategy, it nay be appropriate to consider using mixtures consisting of a number of genotypes of the same species (Ramnde et al. 1988). In this respect, evaluation of collections of

Cover crop beneiiWBn&ficf?sdes @antes de wovMw8 91

accessions of these species is currently underway as part of IITA's ongoing research program. Synergistic effects of growing mixtures of species or accessions have been reported (Ratrunde et al. 1991, Peters et al. 2999). In particular, Peters et al. (1999) noted that species in mixtures tended to have higher crude protein contents than species h sob plots. Such a trend is not immediately apparent from the present results [Table 31, although it could be construed. For example, for Centrosema brarikrrm, Slydosanrhes guianensis ILRZ 164, and Slylosmztthes h a t o ILR? 75 there are indications that the crude protein content in mktmzs was higher than that in single species during the periods of maximum growth; viz. in ?he dry season for C. brasiliarrzrm, the wet and early dry season for S~Iosmthesguianensis, and the wet season for S~1osantheshamata. The methodology described in the present article is suitable forthe evaluation of a wide range of legume species and species combinations. Modifications may be appropriate to take cognizance of, for example, shorter fallow periods, flowering and seed production, effects on subsequent crop yields, and potential for weed control. Ultimately, the design of the evaluation should provide information that can be related to the farmers' circumstancesas well as the biophysical conditions. This would ensure that these potentially valuable species are adopted by i m e r s in order to contribute towards food security and sustainableagriculture in the face of expanding populations.

Acknowledgements The technical assistance of Messrs. Silver Musu, Joseph Adebusuyi, and Sylvester EwansiIra is gratefully acknowledged. The constructive comments from ITTA reviewers improved this contribution, which is published as IITA publication number IITA/99/CPI 18.

References Aiken, G.E., W.D.Pitman, C.G. Chambliss, and KM. Pottier. 2991. Responses ofyearling steers to different stocking rates on a subtropical grass-legumep a s m . . J o d o f M Science 69: 3348-3356 Akobundu, 1.0.and U.E. Udensi. 1995. Effect of Mucum species and fertilizer levels on the control of speargrass (imperafacylidica). Abstract in Weed Science Society of Nigeria 22nd Annual Conference, 6 1 0 November 1995. IITA, Ibarlan. Nigeria Badiane, 0.and C. Delgado. 1995. A 2020 vision for food, agriculture, and the environment in sub-Saharan Africa Discussiori paper 4. IFPRI, Washington, USA. Buckles, D.. A. Eteka, 0. Osiname, M. Galiba, and G. Galiano. (Editors). 1998. Cover crops in West Africa. Contributing to sustainable agriculture. lDRC (International Development Research Centre), Ottawa.Canada, IITb Ibadan, Nigeria, and Sasakawa Global 2000, Comnou, Benin.

92 C m r cmps far natrnal resoume managementPlanles de c 0 l r v e m et g d o n des ressouces ~

Carsky, RJ., S.A. Tarawaii, M. Baker, D. Chikoye, G. Tian, and N. Sanginga 1998. Mucum: an herbaceous cover legume with p o m i a l for multiple uses. Resource and Crop Management Monograph Number 25. IIT" {International Institute of Tropical Agriculture), Ibadan, Nigeria. De Haan, C., H. Steinfeld, and H. Blackbum. 1997. Livestock and the environment. Finding a balance Repost of a m d y coordinated by FAO, USAID, and the World Bank FAO, Rome, Italy. 115pp. De Leeuw, P.N., M.A. Mohamed-Saleem, and A.M. Nyarnu (Editors). 1994. StyImanthes as a forage and fallow crop. Proceedings of the Regional Workshop on the Use of Styiosnnthes in West Africa, 2&3 1 October 1992, Kaduna, Nigeria ILCA, Addis Ababa, Ethiopia. 346pp. Delgado, C., M. Rosegrant, H. Steinfeld, S. Bhui, and C. Courbois. 2999. Livestock b 2020. The next food revolution. Food, agriculture, and the environment Discussion Paper 28. IFPRI,

Washington, USA; FAO, Rome, Italy; and ILIU, Nairobi, Kenya. 72pp. Elbasha, E., P.K.Thornton, and G. Tarawali. 1999. An expost economic impact assessment of planted fosages in West Africa. LfU impact Assessment Series 2. ILRI, Nairobi, Kenya 68pp. Ikwuegbu, O.A., R.M.Njwe, and G. Tarawali.l996.On-farm reproductive performance of the West AErican Dwarfgoat at Ganawuri in the subhumid zone of Nigeria Tropical Agriculture (Trinidad) 73: 49-55. Little, RC., G.A. Milliken, W.W. Stroup, and RD. Wolfinger. 1996. SAS system for mixed models. SAS Institute Inc., Cay,NC, USA 633pp. Maass, B.L., J. Hmson, L.D. Robertson, P.C. Kemidge, and AM.Abd El Moneim. 1997. Forages. Pages 32 1-348 in Biodiversity in Trust Conservation and use of plant genetic resources in

C G W centers, edited by D. Fucciflo, L. Sears, and P. Stapleton. Cambridge Universily Press, Cambridge, UK. Merkei, U. 1996. Erstevaluimg einer Sammlung der tropischen Futterieguminose Aesckynomene h&mk Poiret im Sadwesten Nigerias. Diplomarbeit University of Hohenheirn, ShlttgarZ Germany. 12%~. Mohamed-Saleem, M.A. and H. Suleiman. 1986. Fodder banks+hy season feed supplernentation for traditionally managed cattle in the suehumid zone. World Animal Review 5: 11-17. Muh, L., M. Peters, SA. T a r a d i , and R. Schultze-Kraft 1998. Fallow improvement with forage t e g u m e v t e n t i a l s and constraintsof an integrative technology fir crop-livestock system in subhumid West Afiica. Pages393-398 in Soil fertility managementin West Afn'can landuse systems, edited by G. Renard, A. Neef, K Becka, and M. von Oppen. Margmf Verlag, Weikersheim, Germany. Peters, M., S.A. Tarawali, and i. Alk&amper. 1994. Evaluation of tropical p a m e legumes for fodder banks in subhumid Nigeria. 2. Accessions of Centrosema brasiCianum, Cenrmsema pascaomm, Chamaecrista rofurzdcfolia, and Stylosanfhes hamatcz. Tropical Grasslands 28: 65-73. Peters, M., S.A. Tarawali, R. Schuhze-Kraff,J.W. Smith, and A. Musa 1999. Performance of legumdegume m i m e s under small plot periodic grazing. Journal of Agronomy and Crop Science 182: 25-35. Qi, A., R.H. Ellis, J.D.H. Keatinge, T.R. Wheeler, S.A. Tarawali, and Ri. Summerfield. 1999. Differences in the efl'u of temperature and photoperiod on progress to flowering among diverse Mtlc1(mspp. Journal of Agronomy and Crop Science 182: 249-258.

Cover crop benefiWBdndfioesdes plantes de couvedune 93

Rattunde, H.E.V.M. Ramraj, J.H. Williams, and R.W. Gibbons. 1988. Cultivar mixtures: a means of exploiting rnorphodevelopmental differences among cultivated groundnuts. Field Crops Research 19: 201-2 10. Re&tegui, K., R.R. Vera, W.L. Loker, and M. Vbquez. 1995. On h grass-legume pasture performance in the Peruvian rainforest Experimental Agriculture 3 1 : 227-239. Sanginga.N., B. Ibewiro, P. Houngnandan, B. Vanlauwe. J.A. Okogun, 1.0. Akobundu, and M. Versteeg. 1996. Evaluation of symbiotic properties and nitrogen contribution of Mucum to maize grown in the derived savanna of West Africa. Plant and Soil 179: 19-29. SchultEe-Kraft,R., R.J. Clements, and G. Keller-Grein (Editors). 1997. Centrosema: Biologia, agronornia y utilization. (CIAT Publication No. 208). CIAT. Cali. Colombia. 76Spp. Stace, H.M. and L.A. Edye (eds). 1984. The Biology and Agronomy of StyIosanthes. Academic Press, Sydney, Australia Tarawali, G. and M.A. Mohamed-Saleem. 1995. The role of forage legumes in supplying improved fied for livestock and nitrogen to subsequent crops in the subhumid zone of Nigeria. Pages 263-278 in Livestock and sustainable nutrient cycling in mixed farming systems of subSaharan Africa Volume 11. Technical Papers, edited by J.M. Powell, S. Femandez-Rivera, T.O. Williams, and C. Renard. ILCA, Addis Ababa, Ethiopia. Tarawali, G. and M. Peters. 1997. Compatibility of Sty!osanthes hamata and S&losanthes capitata in mixed pastures in the subhumid zone ofNigeria Pages 91-92 in Proceedings of the 28th International Grassland Congress, 8-17 June, Winnepeg arid Saskatoon, Canada.

Tarawali, G., V.M.Manyong, RJ. Carsky, P. Vissoh, P. Osei-Bonsu, and M. Galiba. 1999a. Adoption of improved fallows in West Africa: Lessons from Mucuna and stylo case studies. Agoforestry Systems (in press). Tarawali, S.A. 1991. Forage legumes for subhumid West Africa: preliminary agronomic evaluation Tropical Agriculture 68: 88-94. Tarawali, S.A. 1994a Evaluating selected forage legumes for livestock and crop production in the subhumid zone of Nigeria. Journal of Agricultural Science 123: 5540.

Tarawali, S.A 1994b. The yield and persistence of selected Brage legumes in subhumid and semiarid West Africa. Tropical Grasslands 28: 80-89. Tarawali, S.A. and M. Peters. 1996. The potential contribution of selected forage legume pastures to c e d production in croplivestock fanning systems. Journal of Agricultural Science 127: 175-282.

Tmwali, S.A., G. Tarawali, A. Larbi, and I. Hansom 1995. Methods for the evaluation of forage legumes, grasses, and fodder trees for use as livestock feed lLRI Manual No. I. international Livestock Research Institute, Addis Ababa, Ethiopia 3 1pp. Tarawdi, S.A., B.B. Singh, M.Peters. and S.F. Blade. 1997. Cowpea haulms as fodder. Pages 313-325 in Advances in Cowpea Research, edited by B.B. Singh, D.R. Mohan Raj, K.E. Dashiell, and L.E.N. Jachi. IRA, Ibadan, Nigeria and Japan International Research Center for Agricultural Sciences (JIRCAS). IITA, Ibadan, Nigeria Tarawali, S.A., M. Peters, and R. Schultze-Kraft. 1999b. Selecting and testing forage legumes for sustainable agriculture and livestock production in subhumid West Africa lLR1 Project Report. ILRI, Nairobi, Kenya 132pp.

94 Cover crops for nahrml resource managemenWlantes de camrture et gestion des ressaurces natureiles

Thomas, D. and J. Sumberg. 1995. A review of the evaluation and use of tropical forage legumes in sub-Saharan Africa Agriculture, Ecosystems, and Environment 54: 151-1 63. Weber, G.1996. Legume-based technologies for African savannas: challenges for~esearchand development. Bioiogical Agriculture and Horticulture 13: 309-333. Weber, G., K. Elemo, A. Awaro, S.T.O. Lagoke, and S. Oikeh. 1995. Striga hermonthica (Del.) Benth. In the cropping systems of the northern Guinea savanna. Resource and Crop Management Division Monograph No. 19. IlTA, Ibadan, Nigeria. 69pp. Wiruock. 1992. Assessment of animal agriculture in sub-Saharan Africa Winrock International institute for Agricultural Development, Monilton, Arkansas, USA. 125pp.

Economic evaluation of systems intercropping food crops with leguminous cover crops in the derived savanna of Nigeria KM. Manyong, G. T i KO.Makind,arrd G.0. Kolawale InfernafiunalImrimte of Tropical Agriculture. !badan. Nigeria

Abstract Simultaneous intercropping is a crop-management strategy that is applied by 'the majority of small-scale farmers in the derived savanna of West Africa. Developing improved systems that are close to farmers' practices is likely to lead to adoption. This paper reports economic results from a 2-year on-station evaluation of four systems (sole maize, maize + Mucuna, maize + Puerarirr, and maize + Pueraria + Mucuna in the first year, each rotated with maize + cassava in the second year) in which food crops were simultaneously planted with leguminous cover crops with and without fertilizer at Ibadan, Nigeria. Systems with Pueraria and those with PueroridMucuna were more profitable than the others and seemed to be promising technologies for simultaneous intercropping of food crops and cover crops for the derived savanna of West Africa. However, these systems were associated with variability in the economic returns that need to be taken into consideration when m e t i n g improved systems to farmers. Jmproved systems that integrate leguminous cover crops with fertilizer application were technically and economically superior to those without fertilizer. This is an indication that combining cover crops with inorganic fertilizer is an efficient strategy to address the issue of low productivity in West African agriculture.

L'association culturale simultanee s'avere une strat6gie de gestion des cultures appliqute par la plupart des petits exploitants dans la savane dirivte de 1'Afiique occidentale. La mise au point de s y s t h e s amtliorks proches des pratiques paysmnes pouirait entrainer leur adoption. Cette communication porte sur les rtsultats Cconomiques de I' evaluation, en station, de quatre systtmes pendant une piriode de deux ans (mars en pur, mars + Mucu~a,mays + Pueraria, et mays -i- Pueraria i.Mucuna au cours de la premiere annte, chaque culture produite en rotation avec du mars + manioc This i s IITA manuscript number IITA/OO/CP/06.

96 Cover craps f ~ natural r resource managemenfllantes de couerture et gestion des ~ e s s o u ~ ~naturelles es

pendant la deuxikme annCe) oh des cultures vivrieres ont CtC simultanCment plantCes, A lbadan (Nigeria) avec des plantes de couvertures de lkgumineuses sans application et avec application d'engrais. Les syst&mes avec Plteraria et ceux avec Ptrerarkd Muctrna se sont rkvCICs plus centables que les autres et semblent Ctre des technologies prometteuses pour l'association sirnulanee des cultures vivritres et des plantes de couverture dans la zone de savane dCrivee d'Afkique occidentale. Cependant, ces systi?mesont prksentC une variabilite de rendements kconomiques qui doit &re prise en compte lorsque les agriculteurs sont ciblks en vue de l'introduction des systimes amdiores. Les syst2mes amiliort?s indgrant les plantes de couverture de ICgumineuses etaient techniquement et economiquement superieurs aux sysdmes sans engrais. Cela est une indication que la combinaison des plantes de couverture et des engrais inorganiques demeure une strategie efieace permettant de s'attaquer au problerne de la kiblesse de la productivite agricole en Afrique occidentale.

Introduction Legumes play an important role in farming systems of the humid and subhumid tropics as sources of human food and animal feed, and for soil conservation and fertilitjl maintenance (Edwards 1989). In many areas of West AMca, use of low-input systems with incluslbn of legumes has shown good promise and varying degrees of success in maintaining h e fertility of upland soils and weed control (Sanginga et al. 1396, Versteeg and Koudokpon 2993). Multiple cropping with legumes can provide two types of benefits for nitrogen (N) supply. The first type is from the direct transfer of N from the simultaneously planted legumes duringthe life ofthe intercropped species. The second type of benefit is from legume residues. The buUc of the N fixed by a legume is made available to food crops after the decomposition of their residues and root nodules (Henzel and Vallis 1977). While the first category of benefits could be noticeable during the sameyear of legume introduction, the other type is filly perceived only as from the second year. Studies s the N benefit to the conducted with cereamegume intercropping gave mixed ~ s u l ton ceieals. Waghmare and S'mgh (2984) observed large increases in sorghum yield and N uptake when simultaneously intercropped with green gram, grain cowpea, and particularly, fodder cowpea, but little benefit when intercropped with groundnut and soybeans. Despite obvious biological benefits from integrating legumes into farming systems, farmersare reluctant to adopt improved systems with leguminous cover crops unless they are economically superior to the existing agricultural practices and can easily fit current farmers' circumstances. There is substantial literature on the economics of relay cropping of herbaceous

Cover cmp beneAtsB6n8fices des plantes dw wuvefiure 97

legumes such as Mucuna with food crops in West Africa (for example, Osei-Bonsu and Buckles 2993,Manyong and HoundCkon 1997,Buckles et al. 1998,Honlonkou et al. 2999, Sinsin and Holvoet 1999, Tarawali et al. 1999). Yet knowledge of their economic evaluation is, however, rather scanty for systems in which legume cover crops are simultaneously intercropped with food crops. It is a well-known fact that simultaneous intercropping is the most popular crop management by small-scale farmers in the derived savanna of West Africa (Steiner 1982). A typical cycle of production involves the cropping of maize (Zea mays L.) in Year 1 and maize intercropped with cassava (Manihot escuienta Craniz) in Year 2 before land is abandoned to fallow. Therefore, simultaneous planting of herbaceous legumes with food crops is expected to increase the likelihood of adoption of cover crops by farmers (Tian et al. 1999). It was with the purpose of evaluating alternative management systems that are very close to f m e r s ' current practices that an on-staiion trial was initiated on simultaneousplanting of food crops with leguminous cover crops over a 2year period. The overall objective was to evaluate ihe economic profitability of such improved systems over one complete cycle of crop production in moist savanna zones of West Africa. Specifically, the objectives of the economic evaluation of the experiment were to: analyze the technical productivity ofthe improved systems assess their economic return identify those suitable for further on-station experiments and on-farm research.

Materials and methods The trial was carried out at the experimental farm of the hternational Institute of Tropical Agriculture (IlTA), Ibadan, in the derived savanna of Nigeria. The predominant fallow vegetation cover of the experimental site was Panicurn marimurn. The experiment was a randomized complete block design wwi four replicates and four ireatments. Maize and cassava were the food crops while Mucuna (Mucuna prurienr var. urilis) and Pueravia (Pueraria phasedoides) were the leguminous cover crops. In Year I, treatments were sole maize (TI is the control), maize + Mucuna (T2), maize + Pueraria (T3), and maize + Mvcuna + Pueraria. In Year 2, leguminous cover crops were not planted; the legume residues from Year 1 were incorporated with hand hoes before maize was intercropped with cassava for each treatment. TI is consistent with farmers' practices in the study area. T2 to T4 were the improved systems. All treatments were laid out in two adjacent sites: with and without fertilizer. It is well known that maize yields are reduced when Mucuna and maize are planted at the same time (Osei-Bonsu and Asibuo 1997)while Pueravia grows slowly. However, the two herbaceous legumes were chosen because they represent the extremes as far as ihe growth rate of cover crops is concerned: Mucuna is fast-growing while Pueraria is

slow-gowing. Plot s k w e n 10 m x 22 m for treatments with fertilizer and 12 rn x 8 n for treatments without fertilizerappli~tion.Plots were large enough to collect rneaninghl data .fbr socioeconomic analyses of labor use (Spencer 1493). In Year 1, maize (crrltivar POP-SR-W) was planted at a spacing of 1 m x 0.25 m (40 000 plantsha). Legume seeds ( M a m a ,P~uerarin,and alternate rows of both)were sown between maize rows on the same day. Three seeds of Munma were planted per hole spaced 20 mapart at 120kg ofseedska while Puermfaseeds was drilled at a seeding rate of 5 kgflna. A mixaue of45-26.30 kg N-PIOI-rC,OJha was applied to treatments with fertilizer only, with 1/3 N applied at planting. The remaining 2M N was applied 3 weeks after planting WAF').Plots were weeded twice, at 3 and 7 WAP.The pruning of Mucum vines was done as needed after the second weeding, All the agricultura1 operations (like planting, weeding, thinning, and p m i n g of M u m vines) were by hand. In Year 2, cassava (TMS30572) at 10 000 plantslha was intemopped with the same maize variety. In the absence of cover crops, weeding (often combined with another operation) was repeated five times for each treatment. The rotation planned over the 2-year experiment is described in Table 1. Labor data were recorded using a stopwatch by an enumerator who was always present in the field during each field operation. The experiment ran over 1996 and 2997.The prices for both inputs and outputs were collected only in 1996 from the local markets. Therefore, the economic analysis was based on 1996 current prices <in 2996, the average exchange rate was N80 = US$I). ANOVA was conducted using SAS (SAS 1985) for treatments with fefiilizer and treatments without fertilizer separately. Statistical analyses were performed on total labor investment (person-days) and productivity (maize and cassava yields) since all the other variables were constant in the systems. Further economic analyses were conducted to calculate the beneficcost ratio (B:C) for each treatment and the marginal rate of return (MRR) and to identifythe dominated

Table 4. Planned rotation for systems intercroppingfood cropswiVl leguminouscover craps over a Zvear ex~erimentin the derived savanna of Nineria. --

TmabTlent

Year 1

Year 2

TI T2 T3 f4

X X+Muc X+Pue X+Pue*Muc

X+WS X+CAS X+CAS X+CAS

X = Maize: Muc = Mucuna; CAS = cassava; Pue = Puerafia. Treatments: T I = Maize only (Contml treatment); T2 = Maize + Mucuna; f 3 = Maize + Pueratia; i 4 = Maize + Mucuna + Puerafia.

Cover crop benefiWBBn4fwsdes plants de oovverfure99

treatments (ClMMYT 1988). The MRR was calculated as follows: MRR = W$-qY (CixJ

where: =

N$ C, Ci

Net revenue for control treatment (TI) = Net revenue for treatment i (i = 2,3,4) = Total variable costs for control treatment (TI) = Total variable costs for treatment i (i = 2,3,4)

Results and discussion Labor investments Over the 2-year period, labor investments varied between 167 and 228 person-daysha for treatments with fertilizer and between 162 and 192 person-daysha for treatments without fertilizer (Table 2). n o s e figures are very close to those (214-229 persondaysha) reported by Chianu et al. (2000) in a long-term experiment in the same ecology. On average, trements with fertilizer required 10% more labor compared to those without fertilizer. That difference in labor use over a complete cycle of production could be due to differences in higher weed densities and crop yields resulting from fertilizer use. Compared to Year I, labor investments h Year 2 for the control treatment (Tl) increased by 3.2% with fertilizer application and 40.4% without fertilizer. The other treatments with leguminous cover crops and fertilizer application had a decrease in the labor costs of 4% for T2,38% for T3,and 26% for T4.This trend was expected because of reduction in weeding due to weed control by herbaceous legumes. SurprisingIy, treatments witbout inorganic fertilizer had an increase in labor Table 2 Productivity of systems intercroppingfood mps with leguminous cover crops over a 2vear ex~erirnsntin the derived savanna of Niaerii. Treatments TI Yield (Uglha)" Maize 2.0' Cassava" 9.0' Labor (person-dayslha) 168.6 Kglmenday 65.2

With fertilizer T2 Y3

l.ga 2.3* 2.4 9.4= 13.P 12.9 166.7 196.7 228.2 67.8 77.9 64.4 -

T1 O.ga

9.3' 169.3 60.2

Without fefilizer T2 T3

0.9 l.Oa l.Oa 10.79.8' 12.4161.7 191.9 166.3 71.7 56.3 80.6

- - --

Numbers with the same letter for a crop are not statistically diifeerent at 5% level for treatments with and without fertilier, separately = On-station yields were adjusted downward by 10% (for maize) and 20% (for cassava) for parity with on-farm irials (Tan et at. unpublisheddata) C. = Year 2 only Treatmenis: T1 = Maize only; T2 = Maize + Mucuna; T3 = Maize * Pueraria * Mucuna.

100 Cover cmps for nalumr resource managemenf/Plantesde aomrture ef gestiondes mssomes nahnenes

investment as follows: 42% for T2,59% for T3,and 28% for T4 for which no clear explanation was found. A large proportion (> 50%) of labor was for weeding. Pueraria is a slow growing mop, which facilitates a quick invasion by weeds and so requires more cmfbl and intensive weeding. M m a grows faster and climbs on maize, which also requires intensive labor for the pruning of vines. This trend on labor allocation to weeding and other f m operationswas observed for all the treatments, as s h o w in Figure 2 far T3. The percent of labor allocated for weeding for treatments without fertilizer was consistently higher (Tl:65%; 72:6796, and T4:65%) than that for treatments without fertilizer (Tl:52%; 'I2: 51%, and T4: 63%). This difference is due to the slow development of herbaceous legumes @mce low canopy cover resulting in poor control on weeds) in the absence of inorganic fertilizer. In Year 2, there was no significant difference at the 5% level in the labor investments among treatments with fertilizerand amongthose without fertilizer. M o r requirements for TI with fertilizer was significantly higher than that of the same trearment without fertilizer. This trend was observed for the other treatments. Among all treatments, T2 had the least labor requirements. Ln Year 2, the labor requirement was significantly higher in TI as compared to the others with herbaceous legumes. However, the significant difference in labor use due to fertilizer for similar mamats h Year 1 disappeared in Year 2 (data not shown). This could be the result of the effect of herbaceous legumes on weed control that led to less labor requirementfor the crops. This result may expiain the l i ~ l difference e in the labor investment over the 2-year period for each treatment with and without fertilizer (Table 2).

Land pmduct"i0@ Average make yield m g e d from 0.9 to 2.0 tlha for treatments without f d l i z e r and 1.9 to 2.4 Mgka for those with fertilizer over the 2-year period, suggesting a large response to fertilizer application by the maize cultivar POPSR-W used in the trials (Table 2). The comparisons of maize yields between Year 1 and Year 2 revealed the eEea of herbaceous legumes on the productivity of the systems. Without,-f maize yield inmased &om an average of 0.4 in Year I to 2.5 Mg/ha in Year 2. Qn airetage, that change represented an increase of 293% (182% for TI, 621% for 7'2, 242% for T3,and 305% for T4). With fertilizer application, the average yield of2.8tf ha in Year 2 represented an increase of only 8% as compared to Year 1 (54% for TI, 87% for T1,103% for T3,and 102% for T4). Therefore, the combination of inorganic fertilizer with mulch residues &om herbaceous legumes in Year 2 could explain the stability of maize yields for treatments with fertiiizer. Vanlauwe et al. (1998) aalsb observed similar benefits of combining organic and inorganic inputs on maize production in West Africa. Results on cassava yields showed that treatments with

Without fettiker

64%

W I fertilizer ~ 10%

12%

51%

U C l d n g URidging MPIanting OW&g

l ~ e s ~ lay@ d ~ e MHrrwesthg

Figure.4.Labor allocationto farming operationsfor systemsintempping food crops with Puerana in the derived savanna of Nigeria.

leguminous cover crops had higher yields compared to the conlrol. Increases io cassava and maize yields indicated that herbaceous legumes had a positive impact on the productivity of food crops. The impact of herbaceous legumes in the f h g systems was even greater in the absence of inorganic fertilizer. Such a finding is important for subsistence farmers who often have no access to inorganic fertilizer in the derived savanna of West Afiica. Wile there was no significantdifference in maizr:yields among trements without fertilizer, significant ditrerences at the 5% level were observed among those with fertilizer. Since there was a significant difference in cassava yields among treatments as well, an economic analysis was required in order to determine which of the treatments would be preferred to the others (CIMMYT 1988).

902 Covercmps fornahrml rescvrce managemenVFlades ds cowerture ef gesfion des resoutzes namnes

Labor produclivity Dividing yields of food crops for each system by its labor investments gave a labor productivity factor (LPF). In a land-abundant area and less capital intensive systems such as in most of the derived savanna of West Ai?iea, LPF is-animpoftant parameter for the recommendation of improved systems to f m e r s because labor is the most constraining factor of production. Results in Table 2 indicated that in the presence of inorganic fertilizer, simultaneous cropping of food crops with Puernria (T3) had the best LPF of 77.9 kg of produce (maize + cassava) per manday. The other treatments were of the same labor productivity. In the absence of inorganic fertilizer, T4 had the highest LPF.Tn such areas where labor is scarce, T4 would be preferred because it outpdormed any other system with or without inorganic fertilizer.

Economic analyses Results from economic analyses for both treatments with and without fertilizer are presented in Table 3. In general, all the &eatments were economically attractive because they gave positive net revenues. Furthermore, the benefit:cost ratios were greater than two. All treatments with fertilizer application gave net revenues at least mice as high as those without fertilizer. Results fiom the dominance analysis for the '"with fertilizer" treatments showed that T2 had higher total variable costs and a lower net revenue than those of TI. Therefore T2 was dominated by T i . Similarly, T4 was dominated by T3. Therefore they were excluded from further economic analyses. No decision could be taken ham Table 3. Economic results of systems intempping food crops with leguminous cover crops over a 2-year experiment in the derived savanna of Nigeria. Treatments

With fertilizer 72 T3

Wnhout fertilizer T2 T3 T4

Totalvariablecasts(Nfha) 24349.5 27161 27365 31930 tabor costs (Nma) 16861.5 16673 19627 22817 Seed casts (Nha) 3000 6000 3250 4625 Fertilizer costs (Nma) 4488 4488 4488 4488

19930 22171 16930 16171 3000 6000

22443 21251 19193 16626 3250 4625

Revenue ( M h a )

52688 56756 34128 35316 18560 21440

60722 63860 41202 39060 19520 24800

32758 2.64

38280 42609 2.71 3.01 0

Maize

cassava Net revenue (Nha) BenefiVcost ratio Dominance analysis

98198 93706 115956 118 852 80118 74826 90036 91212 18080 18880 25920 24640

73848.5 66546 88591 86923 a.03 3.45 4-24 3.72 D D

MRR I)= Dominated: MRR = Marginal rate of return

34585 2.56 0

4.89

Treatments: T I = Maize only; T2 = Maize + Mucuna: T3 = Maize + Puearia; T4 = Maize + Piteraria + Mucuna

7.46

the dominance analysis about the choice betureen TI and T3. The computation of MRR as required resulted in a ratio as high as 4.89 or 489%. Although the econornic return from T1 were very positive @:C = 4.03) a decision-maker who is rational should adopt the improved system represented by T3. Adoption of this improved system would give an additional gain of N3.89 fiom every Naira invested in the process of production. Results from the dominance analysis for the 'kithout fertilizer" treatments were similar to those described above. T4 and T1 dominated T2 and T3.The results on MRR indicated that of the remaining treatments T4 and TI,T4 should be retained because that ratio was as high as 7.46 or 746%. As it was already shown on yield data elsewhere in this paper, the economic profitability of the systems was higher in Year 2 as compared to that of Year Z for all the treatments (Figure 2). K i s diRerence is attributable to the effect of herbaceous legumes, all other things being constant.

Figure2. B:C ratio of systems intercroppinghod cropswith leguminouseovercrops in thederived savanna of Nigeria.

104 Cover cmps for nahrmI resource managemanWiantes de cbuvert~rset geslion des resources nahneRes

Choice of systems with potential far adoption by farmers The ewnomic analyses led to the recommendation of two systems for further analysis and potential adoption by farmers: T3 (food crops + Bueraria) for treatments with fertilizer and T4 (food crops + Pueraria/Mucuna) for those without fertilizer. The improved systems retained were not dominated by any of the other treatments. Besides, the MRR was very high when one moved from the traditional (control) to either of the two recommended systems. The above recommendations are based on the results over 2 years. However, farmers do not always take their decisions about the retention of new technologies on the basis of the whole cycle of production. Adoption over time is a cumulative process. Farmers, especially resource-poor ones, may be reluctant to adopt technologies that do not bring any immediate economic benefits or those that are prone to risk. Moreover, in my farming community, there are always innovators who are ready to take a risk in the testing of new innovations. Therefore, any recommendation for the targeting of improved systems should take into consideration the factors cited above. For treatments without fertilizer, systems represented by T2 and T4 gave very low returns in Year 1 but high benefits in Year 2 (Figure 2). Late adopters and risk prone farmerswould be discouraged by the poor results from Year 1 and might not be willing to pursue the testing of these innovations in the subsequent years. Such improved systems should be best targeted to both innovators and less risk-averse farmers. h Year 1,T3 gave a B:C iatio that was close to that of T 1, the farmer's practice. It is likely that risk prone fanners would be interested in the adoption of T3.For treatments with fertilizer application, fanners may be unwilling to adopt T2 and T4 in Year 1 as compared to T3. Results in Figure 2 can be the basis for the targeting of the improved systems to potential adopters. The higher the difference in the B:C ratio between Year 1 and Year 2 for a given system the less likely such system would be adopted by riskprone farmers because of hi@ instability in the economic results over time. Such a system should mmetinnovators and farmers well endowed in resources such as land and capital. Systems with lower differences should tarpDetresource-poor h e r s . It is interesting to note that, for the 2-year period, farmer's practice with or without fertilizer (Tl) was the most stable of all the systems being compared, that is, the least risky system because the difference in B: C ratio between Year 2 and 1 was the lowest (Figure 2).

Conclusions The results obtained from the technical and economic analyses showed that systems that integrated food crops with leguminous cover crops were technically superior and economically more attractive as compared &I the farmer's practice. Therefore, there is evidence that simultaneousintegration of food crops with herbaceous legumes appears

to be a promising econornicaliy improved system for small-scale farmers in tbe derived savanna of West Africa. The benefits from legumes weie greater in the second year after the legumes were simultaneousIy intercropped with food crops, especially where there was no fertilizer application. It is important to develop simple but very clear extension messages to h e r s that demonstrate h a t the benefits from tbe recommended improved systems ace derivable from the second year and that some sacrifices are required in the first year. The results in this paper also showed that the improvement brought about by the herbaceous legumes was associated with low stability in the ewnomic returns, which could be an issue hthe adoption process by risk-averse farmers. Therefore, targeting of new systems to carehlly selected farmers becomes very important in order to enhance adoption. Since there is a mix of people in any kmiing community (innovators, early adopters, late adopters, laggards) the targeting of a basket of improved systems would be preferred to one single option.

References Buckles, D., A. Etkka, 0. Osiname, M. Galiba, G. and Gallimo, G. 1998. Cover crops in West Africa: contributing to sustainable agriculture. IDRC, Ottawa, Canada; I1T& Ibadan, Nigeria; S d w a Global 2000, Cotonou, Benin. 293pp.

Chlauq 3.N., D.S.C. Spencer, and 1.T. Atobatele. 2000. Labour use and productivity in new Mow systems as alternatives to slash-and-bum agricutbm in the derived savsrnnas of Nigeria Pages429-1238in Fanners and scientists itl a changing environment: assessing research in West Africa, edited by G. Renard, S. Krieg, P. Laurence, and M. von Oppen. Bmceedings of the regional workshop, 22-26 February 1999, Cotonou, Benin. Matgraf Verlage. Weikersheim, Gemany. CIMMYT 2988. From agronomic data to farmer recommendations: an economics training manual. Completely revised edition. Mexico, D.F.

Edwards,C.A. 1989. The importanceof integration in sustainableagriculturalsystems. Ecosystems and Environment 21: 25-35.

Henzel, E.F., and I. Vdlis. 1977. T d e r of nitrogen between legumes and other crops. Pages 7 3 4 8 in Biological nitrogen furasion in farming systems in the tropics, edited by k Ayanaba and P. Dart. J. Wiley & Sons, Chichester, U K Honlonkou, A.N, V.M. Manyong, and N. Tchetche. 1999. Farmers' perceptions and the dynamics of adoption of a resource management technology: the case of MUCUMfallow in sourhem Benin, West f i c a International Forestry Review 1: 22S-235. Manyong, V.M. and V. Nound&on. 1997. Land tenurial systems and the adoption of Mucuna planted fallow in the derived savannas of West Africa Selected paper for presentation at the lntedonal Workshop on Property Rights,Collective Action, and Technology Adoption, 2225 November 1997, ICARDA, Aieppo, Syria Osei-Bonsu, P. and J.Y. Asibuo. 1997. Studies on Mucum ( M m m prurjem var. utiiis) in Ghana Pages 435441 in Technology for sustainable agriculm in sub-Saharan Africa, edited by T.Bezuneh, AM.Emechebe, J. Sedgo, and M. Ouedraogo. Pmceediagsof the OAU/STRC-

106 Cover crops lor nahrral resource managemenVPlantes de wuyerture et gestion des ressources natureRes

SAFGRAD Regional workshop on Tkchnology Options and Transfer Systems for Sustainable Agricultural Production in Sub-Saharan Africa, 2 6 2 9 April 1995, Abidjan, CBte d'ivoire. Osei-Bonsu, P.and D. Buckles. 1993. Controlling weeds and improving soil fertility through the use of cover crops. Experience with Mucum spp. in Benin and Ghana. Bulletin WAFSRNf RESPAO NO. 14: 2-7. SAS 1985. SASR User's guide: Statisticsversion 5 edition. Cary, NC: SAS institute Inc. Pages 414,749-762. Sanginga, N., Ibewiro, B., Houngnandan, P., Vanlauwe, B. Okogun, J.A., Akobundu, LO., and Ventee& M. 1996. Evaluation of symbiotic properties and nitrogen contribution of Mucuna to maize grown in the derived savanna of West Africa. Plant and Soil 179: 119-129. Sinsin, B. and K. Holvoet. 1999. Mucttna corhinchinensis intercropped with maize in agropastoral zones in northern Benin. CIEPCA Newsletter No 4: 6. Spencer, D.S.C. 1993. Collecting meaningful data on labor use in on-farm trials in sub-Saharan Africa. Experimental Agriculture 29: 3946. Steiner, K.G.1982. Intercropping in tropical smallholder agriculture with special reference to West Africa. GTZ, Eschbom, Germany. Tmwali, G., V.M. Manyong, RJ. Carsky, P.V.Vissoh, P. Osei-Bonsu, and M. Galiba. 1999. Adoption of improved fallows in West Africa: lessons from Mucuna and stylo case studies. Agoforestry Systems 47: 1/3:93-122.

Tian, G., G.O. Kolawole, EK. Salako, and B.T. Kang. 1999. An improved cover cropfallow system for sustainable management of low activity clay soils of the tropics. Soil Science 164: 671481. Vanlauwe, B., J. Diels, 0. Lyasse, N. Sanginga, S. Deckers, and R. Merckx. 1998. Balanced nutrient management systems for maize-based systems in the moist savanna and humid forest zone of West Africa, Annual Report No. 1. January 1997-December 1997. IITA. Ibadan, Nigeria. Versteeg, M.N. and V.Koudokpon. 1993. Participative farmer testing of four low external input technologies to address soil fertility decline in Mono Province (Benin). Agricultural Systems 42: 265-276.

Waghmare, A.B. and S.P.Singh. 1984. Sorghum-legume intercroppingand the effects of nitrogen firtilization I. Yield and nitrogen uptake by crops. Experimental Agriculture 20: 25 1-259.

Participatory sydems development Elabom~onde SrjtGrnes participatifs

Quelques performances et contraintes d'adoption du pols dyAngale(Cajanus cajan) et du pois mascate (Mucunapruriens var. uiilis) en milieu paysan dans le Dbparternent de I'atlantique, Republique du Benin

RbumQ La phurie foncibre a induit des modifications des systkrnes de cuIture et des modes d'aces a la tern dans le Ddpatement de I'Atlantique. Les jachhes sont devenues comes, voire inexistantes d m certains cas. Les paysans developpent dans le mCme temps des innovations endogenes d'allongement de la dunk sws culture des sols. Face au probltme d'appauvrissement des sols, le Centre #Action Regionale pour le DCveloppement Rum1 du DGpartement de 1'Atlantique (CARDER Ailantique) a proposd le pois d'hgole (Cajanlcs cajan) et le pois mascate (Mucunapwiem vari& utiIis) pour la jachhre am8liorke. Les tests eRectu6s sur le pois d'Angole e 1988-89 ont rnontri que son association au mars ne crde pas une concurrence importante avec le mals. En gande saison 2989, les rendements de mats grain sont de-1505 kglha et 836 kglha respectivement pour la sole de pois d9Angoleet la sole tdmoin. En petite saison 1989, les rendemenis de mats sont de 1277 k@a pour la sole de p i s d'Angole et 838 kg/ha pour la sole ttmoin. MalgrC ces n5sultats, les paysans n'ont pas adopt6 le pois d'hgole. Les raisons sont

110 Cover crops for natural resource managemenWlantes de wuverture et gestion bes ressources naturelles

que la consommation du pois d'Ango1e n'est pas dans les habitudes alirnentaires des paysans et que le pois d'Angole pousse trks ma1 dans les sols dont la dkpdation est avancee, contrairement au manioc qui y pousse relativement bien. Mieux, le manioc sem6 21 forte densite (densite variant entre 17 000 et 18 000 pieds de manioc/hectare) arnkliore la feriilitC physique de sol par te phenorntne de labour qu'exige sa rkcolte en periode stcha. Un essai diagnostic incluant le pois d'Angole a CtC conduit en 2998-89 pour verifier les hypotheses (1) que I'effet du precedent pois d'Angole est superieur h celui du "manioc dense" et (2) que le "manioc dense" est plus intege au systeme de production des petites exploitations agricoles. Les risultats ont montr6 que le rendement de mais sur la sole de Cczjanus est significativement plus gi-and de celui de la sole "manioc dense" en grande saisoa, mais il ne I'est plus en petite saison. Donc, la premiere hypothbe est vraie pour la seule saison de culture qui suit irnmediaternent la coupe du Cajanus. Lorsqu'on considere la productivitk du travail investi dans les systemes, le '"manioc dense" a une productivite de 216 FCFA par heure de travail investi pendant que le Cajanus e a a 204 FCFAfheure. Ce resultat indique que sur Ie plan Cconomique, le "manioc dense" est plus adapt6 aux conditions des petites exploitations agricoles caractdrisees par la pCnurie fondre, le manque d'argent et une charge en travail Clevt5e. En ce qui conceme le Mucuna, son eRet precedent sur le rendement de mays est significatif pendant deux saisons culturales consecutives A sa jachere. Au dela, les rendements en mars des soles tCmoin et Mucuna ne sont pas statistiquementdiffkrents. L'adoption du Mucum au niveau des petites exploitations agricoles se heme A la non commercialisation de ses graines sur les marches locaux, la non consommation de ses graines pour l'alimentation humaine et la non possibilitti de cultiver sur la parcelle de Mtccuna en petite saison.

Abdmct Land scarcity resulted in changes in the cropping systems and patterns of access to land in the Atlantique Depariment. Fallow periods were shortened and became even nonexistent in some cases. In the meantime, farmers developed innovative local practices which extended land cropping duration. To tackle the problem of soil exhaustion, the Centre for Regional Action for the Rural Development of the Atlantique Department (CARDER Atlantique) proposed the use of C ~ a n u c@an s and M~~a~naprz#riens var. uflis as fallow crops. Trials conducted with Cajanzcs cajan ir. 1988-89 indicated no competition with maize under intercropping. During the major season in 1989, maize grain yields were estimated at 1505 kglha and 836 kgha for the Cajanus cajan rotation and the control treatment, respectively. During the minor season in f 989, maize yielded 1277 kglha

Participatory systems developmenff~/aboiati~ d0 systemes patiicipatifs 111

for the Cajanus cajan rotation and 838 kgha for the con&ol. Despite these results, farmers did not adopt Cajanus cajan. The reasons were that C ~ a n t t scajan is not consumed by farmers and it does not perform well in highly degraded soils as opposed to cassava which has relatively better performance under the same condition. In addition, densely planted cassava (between 17 000 and 18 000 plantstha) improves physical soil fertility through the tillage required for harvesting the cassava in the dry season. A diagnostic trial including Cajanus cajan was conducted in 1988-89 in order to test the hypotheses (1) that the ef5ect of the previous C. cajan is higher than that ofthe densely planted cassava and that (2) densely planted cassava is more integrated in small farmers' practices. The results indicated hat maize yield for the Cajanw cajan rotation was significantlyhigher than that of the densely planted cassava rotation in the major season but such was not the case in the minor season. Therefore, the first hypothesis was positively confirmed only for one cropping season immediately after cutting C. cajan. Return to labor for densely planted cassava was estimated at CFA 2 16/working hour invested, while that of C. cajan was CFA 204lworking hour. This result indicated that economically, densely planted cassava was more adapted to small farmers' conditions characterized by land scarcity, limited financial resources, and intensive labor. For Mzicuna, its previous effect on maize yiefd was significant during the two seasons following its introduction as a fallow crop. Beyond that period, maize yields in the control and M u c m rotations were not statistically different. The adoption of M u m a by small farmers is hampered by the fact that its grains are not traded in local markets, they are not used for human consumption, and it is not possible to cultivate in the Mucuna plot during the minor season.

Introduction Cette communication prksente les principaux resultats de recherche et de prdvulgarisation sur le pois d'Angole (Cajanus cujan) et le pois rnascate (Mucunapruriens var. utilis), deux 16gumineuses proposies par le Centre &Action Regionale pour le Dtveloppement Rural du DCparternent de 1' Atlantique (CARDER Atlantique) pour la jachtre amf5liode. La jachtre arnelioree est proposde dans le cadre d'une meilleure gestion de la fertilite des sols dam le departement de I'Atlantique en proie i une degradation continue des terres cultivees.

Pnkentation du Dbgarternent de IvAtlantique Le Dtpartement de 1'Atlantiqueest situe au Sud-Benin (voir carte). Sa superficie est de 3312 kmz dont 240 000 hectares sont cultivables. La population dont le taux de croissance est de 3.5% est estirnCe a 1 300 481 habitants en 1998; la densitt de la

112 Cover crops for natural m o m managemenVPlantss de muverh*e et gestian des mssaurces natmWs

population est de 393 habitants au km2en 1998. La pluviomdtrie moyeme annuelle est voisine de 1200mm donX 700 i), 800 mm pour la premiere (ou grande) saison pluvieuse et 400 B 500 mm pour la deuxikme (ou petite) saison pluvieuse (CARDERAtlanticpe, 1999). La majorit6 des terres cultivables se situe sur m e sene de plateaux domid par les sols rouges de type Yeme de bme" formks sur le continental terminal. La vdgdtation actuelle sur les plateaux est caract&isCe par m bush &Mif associ6 A des peuplements plus ou mois denses de palmier A huile que I'on retrouve dans les sowprefectures d'Allada, Z&,Abomey-Calavi, Tori Bossito, Ouidah et Kpomasse, soit A l'etat naturel, soit en peuplement industriel par endroits. Les autres formations ve5gdtales sont les cocotiers et des halophytes w le curdon littoral, unbush pr&-littoral constitut de touffes de rhyzophora, et une savane plus ou mois mahdcageuse formde de loutddia et diverses cyptmcdes dans les zones basses. Les autres gmnds types de sols du dhparternent sont Ies sols sableux du littoral, les sols alluviomaires le long des cours d'eau, et les vertisols dms la ddpression de la Lama.

Quelques aspeas de la pmbldmatiquede la feriilit6 dm sols dans le DCpalZernentde I'Atlantique La baisse de fertilitt5 des sols est un problhe important dans le ddpartement de I'Atlantique (Fig. 1). Selon m e ttude hite par cette institution en 1991, la superlicie cultivable disponible par membre de mhage agricole est rt5duiti d'environ un tiers en 25 ans. Cette r6duction de la superficie disponible est due B plusieurs facteurs que sont une pression dbmographique poussde, une occupation ou une immobilisation des terres par des non agriculteurs, I'urbanisation et la vente des tares, et enfin une occupation des terres dans certaines regions par des indhltioas btatiques. Pour la phipart k s agriculteurs, la penurie foncitm ainsi cr&e a des incidences sur le systbe de culture et les modes d'acces aux terres. Les modifications induites au niveau du syst2me de culture soot notamment : la rtSduction de la dmde ou i'absence de jachbs naturelles ainsi que l e m superficies l'augmentatioa des pourcantages des superficies de ma'is et de manioc dans les exploitations agricoles en w e d'assuter l'autosufisance en aliments de base (le mais surtout) le d6veloppement de techniques d'allongement de la duxtSe sous culture des sols tel que le "manioc dense" (manioc segC B m e densiteS comprise atre 17 000 et 18 000 plantsha), Ie billomage, l'ameublissement supeficiel du sol A la houe et ie non brCllage des rksidus de dcolte et de satclage. Au niveau des fomes d'acchs A la terre,la vente et la location des terns oat pris de I'ampleur au dtstrhent des dons, le p s t B titre gmtuit et le mdtayage qui au contraire sont relativement en rdgression. Daas ces conditions, ce sont les fonctiomaites, les

Psrt@aiiory systems develo~wUEIabom~on de s y s f ~par$cipafifs s 413

comesants et les gros propribtaires teniens qui sont les miew lotis. Les petits et

moyens agricuIteurs am revenus faibles en general se retrouvent ainsi dans un nouveau syseme f o m e n t rnoneWb. Ils sont du coup d6ikvorisds par rapport aux premiers. Sournis a des conditions financi&resparticuliBrement dEclles, ils sont quelquefois obliges de vendre me partie de leurs terns, aggravaat encore leur situation foncikre dkjit prgcaire cara&ris&e par des champs pauvres et un aces dificile aux terns d'aumi par la location (fernage en esphes, le "Zoundanou" en langue locale). C'est pour tenter de briser ce cede vicieux que le CARDER Adantique a propose dew innovations exog&nesdans la rotation des cultures a savoir, le pois d'hgole {Cajanus cajan), le pis mascate (Mucuna pnrriem var.

Figure1. Schema relationneldeshcteurs libB la baissedefertilit6des solsdamsle Dlpartement de I'Bntique.

444 Cover wps far nalvral resoresourar managmnenVPIanfesde muvsrtum et @?stiondes ressomes natureflBS

m'tb).L'objectif de ces introductions est d'ambliorer le statut organique et le niveau d'azote du sol en w e d'une amtSlioration des rmdements des cultures, celui du mars

notaament.

Les innovations exp4rimentb Le pols d'hngole D e u mvaux ont tit6 mends sur cette innovation en 1988 et 1989. Le premier est un test de prkvulgarisation dont I'objectif est de voir dans quelles mesures cette lbgumineuse s'adapte au syst&meen aise avancee du point de vue de 1a fertilitb des sols. Le second est un essai diagnostic qui compare le C@~nush une innovation endogbe, le 'banioc dense" sur les plans agronomique et socioCconomique. Son objectif est d'identifier les avantages comparatifs susceptibles de hiner ou d'empecher I'adoption du Cajanus.

Le test de priwlgarisation L'objectif de ce test est de mesurer les effets de iajach&rede pois d'hgole sur dew cultures de mafs qui lui succedent.

Quatom paysans

ont abritd le test; chaque paysan repdsente un bloc alkatoire compla compose de deux soles ayant le mdme passe cultural, une sol&pour le pois d'Angole et une pour le thoin, le mas. Les paysans sont ainsi assimilbs h des blocs disperses. Ils ddcident desjours de semis, d'entretien et de rkcolte. Sur toutes les soles, ies semis de mays et de pois d'hgole sont efFectues le meme jour*En ce qui concerne la dens& de pois d'Angole, elle Ctait de 1 n x 0.5 m i3 3 graines par poquet. Celle du mais est celle que pratique habituellement le paysan dans son champ. Les successions cuiturales sut les deux soles au cows des mt5es 2988 et 1989 sont presentees au Figure 2.

Rbultats et discussions En grande &eon 1988, le rendement de mais 1I'hecme est de 1235 kg sur la sole thoin come 1170 kg pour la sob de Cqanw. La variable analysde est le rendernent de ma%par plant afin de voir si la densite de Cajanus proposde influence de fapn significative le rendement par plant du mars assmid. Ce mdement est de 37 g par plant sur la sole Cajamcset 36 g pour la sole thoin. Ces dew rendements ne soat pas si9nifidvment diffients au seuil de 5%. On en conclut que la densite de Ccrjam propost%ne cornpromet pas de fagon significative le rendement par plant du mais qui 1ui est associt5. En 1989, le Cajanus a eSte coupe au debut de la grande saison, puis sa

J P M A M J J A S O M D J P M A M J J A S O N b

Figure 2 Catendrier des systbmes test& en 1988-89, Cajarfus {A), mars continu (B),et manioc

dense (C).

sob semde en mdis c o m e sur le timoin. Les rendements obtenus sont significativemen? diffBrents au seuil de 5% au cours de la p r i d e et petite saisons (Tableau 1). Le Celts dompense non seulemeat la perk de la petite saison 1988, mais degage un e x d e n t global de 293 kg. Mdgre cette performance moyenne, le Cajanw n'a pas did adopg par les paysaris. A ceh, les paysans avmcetlt plusieurs &om. y a d'abord leproblhe d'habitude alimentaire, les paysans ne consomment pas habituellement les m e s de Cajanrcs. Ensuite, sur ceniaim sols t k s pauvres. le Cajanus a m m u un tr&s Gb1e develop pement 18 oh au conmire le manioc pousse relativement miem. La jachere de manioc semd B forte densiid ('hanioc dense" est m e des techniques commaen?u&&s par la plupart des payh p p e s par la p6nurie fonciere. La densitd du manioc vane entre 27 090 et 18000 plants de manioc b I'hectare. Pour avok assez de iiti&resur ces sols dpuisGs, laisser la jach&rede Cajmzm m e aunk encore sur place se& nkessaire, ce qui serait difficile & rddiser pat les paysans qui on?de faibles supeficies. TaMeau 1. Rendement moyen (kglha) de mays sur Ies s a l de ~ Cajanus et du ternoin en 1988 et 1989. Sole de

Cajanus Omde saison 1988 Petite =ison 1988 Grands saisan 1989 Petite saison 1989 Cumul de 1588 ZI1989

Sole Urnoin

1170

1235 850

1505 1277 3992

836

Soume: Adapt6 de Totongnun st al. (1990).

838 3759

D i r e n c e enbe I s2 soles PPDS

--85065

+ 669

* 439 * 193

W(%)

32.7

325

20.3