Interactions among Input Levels, Management Practices and Yield of Transplanted Leaf Lettuce

STUDY IN AGRONOMIC SCIENCE: INTERACTIONS AMONG INPUT LEVELS, MANAGEMENT PRACTICES AND YIELD OF TRANSPLANTED LEAF LETTUCE Introduction California is the largest production center of crisphead lettuce (Lactuca Sativa) in the world. Most of the U.S. supply during the winter originates in the Imperial Valley and the Salinas-Watsonville area provides the bulk of California’s summer shipments. In California’s Imperial Valley lettuce is planted from September to November and harvested from midDecember to mid-March (Note 1). Lettuce is primarily grown on fertile, well-drained soils. Another major consideration is temperature. Lettuce growth in midwinter is slowed by cold weather as nutrient uptake is reduced and thus head size is reduced (UCAE 1978: 6). Furrow irrigation is the most common method of irrigating lettuce. Lettuce is highly responsive to nitrogen and commercial lettuce growers in California use high fertilizer application rates. Early lettuce growers in California produced organically grown lettuce crops, using animal manures, fishmeal, tankage, dried blood and cottonseed meal as nitrogen and phosphorous sources. Green manure legume crops such as cowpeas, vetch and alfalfa were common (UCAE 1978: 22). Land preparation in the Imperial Valley is done with discs and landplanes, and lettuce beds are made with double-faced listing shovels.

The objective of the investigations reported in this paper was to evaluate the effect of two levels of fertility management, organic manure and chemical fertilizer (N, P and K), and two levels of tillage, manual and mechanical, on the growth and yield of transplanted leaf lettuce, and on labor use and distribution. The experiment was conducted from April 6 to May 11, 1985 and field study results were submitted June 11.

Materials and Methods The experiment site was located at the University of California, Davis at approximately 38 N latitude and 122 W longitude. The experiment was performed on Yolo Loam, a deep, well-drained soil, neutral in reaction, and well supplied with all essential nutrients except nitrogen (re: Williams 1966). Maximum and minimum soil temperatures at 10 centimeters were 78o F (5/1-5/5) and 61o F (4/22) during the period of experiment, respectively (re: Appendix climatology data). At 20 centimeters, maximum and minimum temperatures were 72o F (5/2-5/6) and 61o F (4/22), respectively. Precipitation during the experiment was 0.36 inches, and total evaporation was 12 inches. Maximum and

1

minimum air temperatures at two meters were 90o F (4/14) and 37o F (4/22), respectively.

The experiment used a 2 x 2 factorial design with three replications. Plot size was 12.5 X 50 feet, and total net area was 150 X 50 feet. The experiment used two different levels of tillage, manual and mechanical, and two levels of resource inputs, organic manure and chemical fertilizer (N, P and K). Manual tillage consisted of two passes with a rototiller in second gear in land preparation, and manual hoeing in seedbed preparation. Mechanical tillage consisted of land preparation with a tractor-drawn harrow-disc (two passes), and seedbed preparation with a tractor-drawn lister (Note 2). Organic manure treatments consisted of application of composted manure, which was broadcast, raked and incorporated with the rototilling operation in the manual tillage, and with the discing operation in the mechanical treatments. On April 23, fish emulsion (5% N content) was applied at a rate of 250 ml per plot.

Chemical fertilizer treatments consisted of preplant NPK application by broadcasting and incorporation with the rototilling or discing operation.

Application of N (as NH4NO3) was 1.3064 kg/plot of elemental nitrogen, phosphorus, as CaCH2PO4 was 0.5806 kg/plot and potassium as K2SO4 was 0.5806 kg/plot (both quantities were elemental as well). On May 1, a side dressing of NH4NO3 containing 0.6532 kg/plot of elemental nitrogen was applied.

The lettuce, Black seeded Simpson, was sown on March 1 in seedling trays, grown in the greenhouse and transplanted on April 6 at an attempted intra-plant spacing of 20.3cm. Furrow irrigation began on this date, with irrigation twice per week during the experiment. Bird nets were used, and the experiment site was fenced in with chicken wire, with soil moved to cover the fence base against intrusion by small animals.

On May 1, manual weeding took place. Irrigation ended on May 7, and the lettuce was harvested on May 11. No insecticides were used in the experiment.

Sampling was done in the two outside rows of each treatment plot. At weekly intervals (Dates: 4/12, 4/19, 4/26, 5/3, 5/10) ten plants were taken from each of the sample rows for dry matter weight measurement. The two center rows were left intact for harvest. At harvest, 30 feet of the most uniform section of each of the two center harvest rows (a harvest area of 1.524m X 9.144m) was selected for measurement of fresh weight yields, which was done on platform scales in the field. Harvest sample plants were trimmed before weighing, while dry matter sample plants were not trimmed. Dry matter weight was measured after oven-drying of the untrimmed sample plants. Common management components of the experiment were weeding, irrigation, transplanting, and harvest.

2

Results and Discussion Agronomic aspects. The tests showed the chemical fertilizer significantly improved the rate of plant growth in terms of dry matter weight (gm/plant;) (Chart 1: Dry Matter Accumulation; Chart 2: Least significant difference values at LSD 0.05) and significantly increased fresh weight yield (kg/ha) (Table 1). The dry weight per plant and the fresh weight yield were both significantly higher at harvest for the chemical fertilizer lettuce than for the organic manure lettuce. There was no significance between tillage treatments, thus the only significant effect in terms of growth was due to fertility management. A large observable difference was noted between the organic manual and organic mechanical fresh weight yields, however. This observable difference might be worth further investigation because of possible interaction effects between bed size and organic matter. The wider manual beds might have provided a greater volume for roots to search for nutrient sources than the narrower mechanical beds.

A post-harvest bitterness test was conducted and showed that chemical lettuce was generally considered more bitter. Increased stress on lettuce can increase bitterness. The organic plots were observed to have more soil moisture due to the greater content of soil organic matter. The chemical fertilizer plots, with less organic matter content, were found to be dryer and harder from lack of soil moisture. Since nitrogen was not limiting, this suggests that the chemical fertilizer lettuce had water stress which might have caused plant bitterness (Note 3).

The nitrogen content of the organic manure was 1.5% of the manure dry matter weight. Yields might have been greater for the organic lettuce if better quality organic manure had been selected for the experiment.

3

Chart 1. Dry Matter Accumulation

Note: Dates listed are sample dates.

Chart 2. Least Significant Difference Values

It is likely that the manure had lost nitrogen from leaching and volatization in storage in the field, and the relatively higher carbon to nitrogen ratio might have tied up nitrogen in the organic plots.

Plant population a harvest was highest for the chemical fertilizer mechanical treatment and lowest for the chemical fertilizer manual treatment (Table 1). Attempted interplant spacing at transplanting was 20.3 centimeters, but later measurement showed that chemical fertilizer 4

mechanical interplant spacing was the least, 21 cm, while chemical fertilizer manual was the greatest, 22.2 cm. This suggests that the variation in interplant distance between these two treatments affected the plant population at harvest and thereby the total fresh weight yield per hectare in favor of the chemical fertilizer-mechanical treatment. Further investigation should be conducted to determine yield per hectare of these treatments with identical interplant distance. The mean fresh weight (Table 1) showed lower values for organic lettuce, suggesting nutrient stress due to lack of nitrogen.

Table 1. Plant Weight, Population and Yield at Harvest Treatment OM/MAN OM/MECH CF/MAN CF/MECH

Plant Weight, Population and Yield at Harvest Fresh Weight Plant Population Fresh Weight Yield 187 61069 11395.5 151 61355 9257 219 59130 12952.7 216 62503 13513.4

Detail Fresh Weight: Plant Population: Fresh Weight Yield:

mean plant weight (grams/plant) per hectare kg/hectare

(LSD 0.05)

Air temperature does not appear to have had adverse effects on lettuce growth. According to Gardner and Pew (1979), when mean air temperature falls below 13o C (39oF) for a week or longer, lettuce growth and nitrogen uptake are reduced. But at no point during the experiment did this occur (re: Appendix climatology data).

Several pests were observed during the experiment. Ground squirrels (Sytellus Beechyii) penetrated the fence, but no significant damage occurred. No bird damage was observed. Cabbage loopers (Trichopolus Ni) were evenly distributed on all plots, with a ratio of one per 20 plants, approximately. Few cucumber beetles were observed. Aphids infested the plots, but to a greater degree in the chemical fertilizer plots (810/leaf) than in the organic manure plots possibly due to the greater nutrient content. Ladybugs from the surrounding area were observed as well and fed on the aphid population. A high population of pin nematodes was observed, but they are not known to attack lettuce. Many other species of nematodes were observed but none attacked the lettuce roots. At transplanting, several tomato plants, Early Pack 707, were planted in order to observe root knot nematode population, a nematode known to attack lettuce. Although tomatoes are more susceptible to root knot nematode infestation, none were observed, and no lesions were found on the plant roots, which were in healthy condition. In sum, no significant yield damage occurred due to pests, but the high aphid

5

population would have reduced the selling quality of the chemical fertilizer lettuce.

Economic Aspects. Data showing inputs, labor and other costs, as well as yield, gross return and net return for each of the treatments are presented in the partial budgets for Yolo County and a hypothetical experiment in Egypt (Table 2, Table 3). Total gross return is equivalent to the yield multiplied by an assumed $0.75/kg fresh weight price for lettuce in Yolo and $0.25/kg for Egypt (with lower assumed labor costs as well: manual labor at $0.50/hour for Egypt, $4.50/hour for Yolo, and tractor driver costs at $2.00/hour for Egypt and $12.00/hour for Yolo).

Gross returns between chemical fertilizer plots and organic manure plots were significantly different. Chemical fertilizer-mechanical treatments had the greatest gross return and organic-mechanical the least in both Egypt and Yolo. Average gross return of chemical fertilizer plots was 28% higher than that of organic plots in both Yolo and Egypt. Average net return (Note 4) for chemical fertilizer plots was $1903.85/ha, while organic manure plots had a negative average net return of -215.9/ha in Yolo. In Egypt, organic manure plots did not produce negative average net returns, but chemical fertilizer plots gave 124% higher average net returns. In both Egypt and Yolo, the chemical fertilizer treatments yielded the greatest net returns, at $1341.35/ha and $2073.6/ha, respectively, while organic manure-mechanical performed the worst of all treatments in terms of net returns for both Yolo and Egypt.

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Table 2 Partial Budget, Yolo Partial Budget for Transplanted Leaf Lettuce Experiment in Yolo County: Per Hectare Basis Operation/Input Treatment OM/Man OM/Mech CF/Man CF/Mech Labor Cost Labor Cost Labor Cost Labor Cost (hrs) ($) (hrs) ($) (hrs) ($) (hrs) ($) Land/Seedbed Prep Manual bedding 71.7 322 0 71.7 322.8 0 0 Rototilling 27.3 122.85 0 27.3 122.85 0 0 Discing 0 1.05 12.6 0 1.05 12.6 Listing 0 1.2 14.4 0 1.2 14.4 SUBTOTAL 99 445.73 2.25 27 99 445.73 2.25 27 Transplanting Labor Transplants SUBTOTAL

774.9 774.9

Fertility Mgt Inputs: Manure (133.9 T/ha) N (?kg/ha) P (?kg/ha) K (?kg/ha)

3487 320 3807

774.9 774.9

3487 320 3807

857.5 857.5

86

103.3 20.1 5.7 0 0 129.1

464.85 90.45 25.65

Weed Control Labor

464.85 90.45 25.65

934.85

12.9

58.05

50

225 100 383.05

Harvest Plants/ha Seconds/plant Labor/ha SUBTOTAL

110 110

495 495

TOTAL (Labor/TVC)

1175.9

6065.63

61069 6.5

11396 8547 -2136.75 6410.25 344.62

168.7 40 20

86

103.3 20.1 5.7 0 0 129.1

62.9

3858.75 320 4178.75

267.9 168.7 40 20

Labor Manure hauling Manure spreading Spraying Fish emuls.

Broadcast NPK Band N topdr.

SUBTOTAL

Yield (kg/ha) Gross Return -25% Share crop Net Gross Return Net Return

857.5

3858.75 320 4178.75

267.9

Fish Emulsion N (?kg/ha)

Irrigation Labor Pumping cost SUBTOTAL

857.5

934.85

0 0 0 8.6 29.3 37.9

12.9

58.05

50

225 100 383.05

62.9

61355 6 102.2 459.9 102.2 459.9 1154

5983.5

9257 6942.75 -1735.69 5207.06 -776.9

7

38.7 131.85 399.29

0 0 0 8.6 29.3 37.9

38.7 131.85 399.29

12.9

58.05

12.9

58.05

50

225 100 383.05

50

225 100 383.05

62.9

59130 7 115 517.5 115 517.5 1089.7

5552.5

12953 9714.75 -2428.69 1286.06 1733.5

62.9

62503 6.9 119.8 539.1 119.8 539.1 1080.35

5527.2

13512.7 10134.5 -2533.6 7600.8 2073.6

Table 3. Partial Budget, Egypt Partial Budget for Transplanted Leaf Lettuce Experiment in Egypt: Per Hectare Basis Operation/Input Treatment OM/Man OM/Mech CF/Man CF/Mech Labor Cost Labor Cost Labor Cost Labor Cost (hrs) ($) (hrs) ($) (hrs) ($) (hrs) ($) Land/Seedbed Prep Manual bedding 71.7 35.87 0 71.7 35.87 0 Rototilling 27.3 13.65 0 27.3 13.65 0 Discing 0 1.05 2.1 0 1.05 2.1 Listing 0 1.2 2.4 0 1.2 2.4 SUBTOTAL 99 49.52 2.25 4.5 99 49.52 2.25 4.5 Transplanting Labor Transplants SUBTOTAL

774.9 774.9

Fertility Mgt Inputs: Manure (133.9 T/ha) N (?kg/ha) P (?kg/ha) K (?kg/ha)

387.45 320 707.45

428.75 320 748.75

774.9 774.9

387.45 320 707.45

857.5 857.5

86

103.3 20.1 5.7 0 0 129.1

Weed Control Labor

418.45

12.9

6.45

50

25 100 131.45

Harvest Plants/ha Seconds/plant Labor/ha SUBTOTAL

110 110

55 55

TOTAL (Labor/TVC)

1175.9

1361.87

61069 6.5

11396 2849 -712.25 2136.75 774.88

168.7 40 20

86

103.3 20.1 5.7 0 0 129.1

62.9

51.65 10.05 2.85

428.75 320 748.75

267.9 168.7 40 20

Labor Manure hauling Manure spreading Spraying Fish emuls.

Broadcast NPK Band N topdr.

SUBTOTAL

Yield (kg/ha) Gross Return -25% Share crop Net Gross Return Net Return

857.5

267.9

Fish Emulsion N (?kg/ha)

Irrigation Labor Pumping cost SUBTOTAL

857.5

418.45

0 0 0 8.6 29.3 37.9

12.9

6.45

50

25 100 131.45

62.9

51.65 10.05 2.85

61335 6 102.2 56.1 102.2 56.1 1154

1359.25

9257 2314.25 -578.56 1735.69 376.44

8

4.3 14.65 247.7

0 0 0 8.6 29.3 37.9

4.3 14.65 247.7

12.9

6.45

12.9

6.45

50

25 100 131.45

50

25 100 131.45

62.9

59130 7 115 115

57.5 57.5

1089.7

1193.6

12953 3238.25 -809.56 2428.69 1235.07

62.9

62503 6.9 119.8 59.9 119.8 59.9 1080.35

1192.3

13512.7 3378.2 -844.55 2533.65 1341.35

Partitioning of total variable cost (TVC) of each treatment by field operations shows that variable cost as a proportion of TVC for weeding, irrigation and harvest were similar across treatments. (Chart 3) However, land preparation variable costs were only 0.4-0.5% of TVC in the mechanical tillage plots (due to rounding, these values are shown as 0% and 1% in the table below) compared to 7-8% in manual tillage plots.

Fertility management was only 7% of TVC in the chemical plots compared to 15-16% in the organic manure plots. Transplanting was by far the costliest operation for all treatments, representing from 63% to 76% of TVC. As a percentage of TVC, transplanting variable costs were somewhat lower for manual tillage (63-68%) than for mechanized tillage (70-76% of TVC). Refer to Chart 3 next.

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Chart 3. Field Operation Cost (% of TVC by Treatment)

Labor cost ranged between 91% to 100% of variable cost of each operation for all but two operations: Irrigation (between 58-59% for all treatments) and fertility management (62% for organic manure and 42% for chemical fertilizer treatments, respectively); labor cost data are reported here without a corresponding table.

Labor use and distribution data (Table 4) show that transplanting was the greatest labor sink for all treatments, absorbing from 66% to 74% of total labor used. The organic plots absorbed more labor overall in terms of person-hours than the chemical fertilizer plots. A similar percentage of total labor was used in weed control, irrigation and harvest for all 10

treatments. Mechanical tillage plots absorbed less labor (0.2%) for land seedbed preparation than manual plots (8-9%) and chemical fertilizer plots absorbed less labor (3.5%) than organic manure plots (11%) in fertility management.

Table 4. Labor and Labor Distribution

TREATMENT

Labor and Labor Distribution by Treatment and Operation OM/MAN OM/MECH CF/MAN ph/ha %TL ph/ha %TL ph/ha %TL

CF/MECH ph/ha %TL

FIELD OPERATION Land-Seedbed Prep 99 8.4 2.25 0.2 99 9 2.25 0.2 Transplanting 774.9 66 857.5 74.3 774.9 71 857.5 79.4 Fertility Mgt 129.1 11 129.1 11 37.9 3.5 37.9 3.5 Weed Control 12.9 1 12.9 1 12.9 1 12.9 1 Irrigation 50 4 50 4.3 50 4.6 50 4.6 Harvest 110 9 102.2 8.9 115 10.5 119.8 11 Totals 1176 99 1154 100 1090 100 1080 100 Notes: ph/ha and %TL refer to "person-hours per hectare" and "percentage of total labor," respectively.

Total of percentages may not add up to 100% due to rounding.

The data presented here would suggest that alternative methods of transplanting to improve labor use efficiency should be researched, including the possibility of direct seeding instead of transplanting. Labor scarcity has been noted as a problem in Egyptian agriculture, and more efficient methods of transplanting, or direct seeding, would be advisable to prevent labor bottlenecks in lettuce-producing rural areas. As well, reducing labor use and costs would make lettuce growing a more profitable enterprise in both Yolo and Egypt since it is the greatest labor sink. For example, if labor costs per hectare could be reduced by 50% for the transplanting operation, Yolo chemical fertilizer-manual farmers could double their net returns per hectare (Note 5). Egyptian chemical fertilizer-manual farmers would gain less, only 15% over previous net return per hectare. (both values exclude increased cost for the alternative planting method and therefore should only be used as a rough estimate).

Because fertility management was determined to be the significant factor in plant growth, more consideration should be given to the value of chemical fertilizers. Comparison of relative investments for fertility management inputs shows that N-P-K chemical fertilizer costs less, 11

$228.00/ha, than organic applications of manure and fish emulsion, $353.00/ha yet produced significantly higher yields. As well, the reduced labor use and labor costs per hectare associated with chemical fertilizer use suggests the advantage of chemical fertilizers in fertility management. As previously noted, chemical fertilizer application reduced fertility management variable costs to only 7% of TVC in both chemical fertilizer treatments compared to 15% of TVC in the organic manure treatments (Chart 3). Thus, all these factors should be considered in making recommendations on fertility management for low income Egyptian farmers.

Tillage was not found to be significant in explaining plant growth, but some comments on method of tillage can be made. The poor yields and net return of the organic manure-mechanical treatment compared to the organic manure-manual treatment for the reasons already discussed suggest that mechanical tillage should not be adopted in organic manure farming systems until further research is done to explain the large observable yield differences. Although the chemical-fertilizermechanical treatment had greater fresh weight yields per hectare than the chemical fertilizer-manual treatment, further investigation should determine how yields would differ if interplant spacing of both treatments were the same. In sum, it would not be advisable to favor mechanical tillage over manual tillage until further research is conducted.

Without mechanization, Egyptian farmers could still benefit considerably for chemical fertilizer applications. Farmers might then choose independently to invest profits from their chemical fertilizer systems into machinery for mechanized tillage operations due to labor scarcity and rising labor costs in agriculture. For farmers already considering or using mechanical tillage, perhaps increasing bed width and reducing clod size and numbers through more discing would help increase yields, although such benefits have yet to be determined by experimentation. Another important consideration concerning mechanization in Egypt is legal: Land must be divided up for certain family members. If the average Egyptian farm size is presently one acre, benefits from mechanization, which depends on land size for success, will decrease over time.

The gross returns/variable costs ratio is a useful measure of relative profitability of a farming system where, where values above one indicates positive returns to farmers. Values have been calculated for each treatment in Yolo and Egypt; see Chart 4 next.

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Chart 4. Gross Returns to Variable Cost Ratio

Given the assumptions for Egyptian and Yolo prices and labor costs, each of the treatments are relatively more profitable in Egypt than in Yolo in terms of the gross returns/variable cost ratio. Ratios of 2 and above in the Egypt case may be considered above average (Note 6).

In closing, the research conducted in this experiment had been particularly useful in determining the value of chemical fertilizers in fertility management and in comparing the four treatments of the experiment. As an extension of the investigations reported in this paper, other topics of future research might include: interactions between bed size and organic manure, lettuce plant yields using higher quality organic manure, organic manure contribution to soil moisture in hot climates, and long-term effects of chemical fertilizer and organic manure use on soils.

Notes 1.

2.

3.

4.

5.

6.

Information on lettuce production in California and the Imperial Valley was provided by V. Rubatsky, Vegetable Crops Cooperative Extension, UC Davis.

A D4 Caterpillar tractor was used for the discing and a wheeled John Deere for the listing.

It should be noted that there were no apparent effects of such water stress on yield.

Net return = gross return net of total variable costs (TVC) and 25% share crop.

Proper analysis requires accounting for the cost of any additional machinery.

See Cassman, et al., (1984:19) for values in Egyptian soybean farming.

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Appendices Climatological Data for Davis, California Table 5. April 1985

Day 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

max 78 81 85 85 83 84 77 77 84 78 74 75 87 90 89 70 68 66 70 67 61 64 72 79 77 70 79 83 78 82

min 44 46 50 55 51 46 43 47 45 44 45 46 48 52 56 48 46 42 43 46 49 37 43 51 54 56 59 48 48 47

max 77 82 85 84 82 83 77 78 83 77 73 75 86 88 88 68 69 66 68 68 61 61 72 77 75 69 79 83 76 82

min 50 52 54 63 57 49 45 53 59 49 50 52 53 58 54 50 49 46 48 50 50 42 48 55 53 54 63 51 51 51

Climatological Data for Davis, California: April 1985 Soil Temperature Prec Evap 10cm 20cm 50cm max min max min mean totals 62 54 55 52 55 0 0.3 66 47 58 56 57 0 0.16 68 61 61 58 59 0 0.22 70 63 63 60 61 0 0.39 70 65 64 62 62 0 0.59 73 65 65 63 64 0 0.25 72 65 65 63 64 0 0.24 70 64 64 62 64 0 0.2 70 64 66 65 64 0 0.22 74 67 67 64 66 0 0.28 71 66 66 64 65 0 0.18 72 64 66 64 65 0 0.22 73 66 67 65 66 0 0.31 76 68 68 66 67 0 0.26 78 70 70 68 68 0 0.36 75 69 70 68 69 0 0.31 73 64 68 64 66 0.34 0.19 68 62 65 63 66 0 0.14 69 62 64 62 65 0 0.24 69 63 65 63 66 0 0.29 67 64 64 63 65 0 0.17 65 61 63 61 64 0 0.11 68 61 64 62 64 0 0.26 71 64 66 63 65 0 0.4 71 66 66 65 66 0 0.59 69 64 66 64 66 0 0.66 70 64 66 64 66 0 0.57 75 67 67 65 66 0 0.6 75 68 68 66 67 0 0.36 75 68 69 67 68 0 0.25

High Low Mean Total

90 61 77

59 37 48

88 61 76

63 42 52

78 62 71

Air Temperature 2m

15m

70 47 64

70 55 65

68 52 63

14

69 55 65

0.34 0 0.01 0.34

0.66 0.11 0.31 9.32

0.5m 104 27 51 150 250 72 72 42 36 111 78 51 68 28 96 128 77 59 103 76 80 87 64 151 245 348 230 118 106 62 348 27 106

Wind 2m 10m 2m passage direction 149 195 CALM 48 76 NW 78 108 NW 175 256 NW 353 424 N 106 134 WNW 107 144 N 65 84 NW 64 90 SW 152 200 W 123 170 W 79 100 N 98 0 N 49 0 NE 139 0 SW 185 243 W 114 144 SW 91 119 CALM 153 193 N 109 85 W 114 113 SE 130 174 NW 91 83 CALM 203 224 N 321 389 NW 452 567 NW 299 357 N 164 112 S 147 135 W 87 47 CALM 452 48 148

567 0 184

Table 6. May 1985.

Day 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

max 86 88 83 77 82 84 74 76 78 77 69 70 83 88 85 86 75 74 81 87 85 93 93 88 84 73 68 67 64 72 80

min 45 51 48 52 43 52 44 42 41 47 42 43 45 47 56 40 45 42 46 48 49 52 57 49 49 50 50 53 40 45 52

max 86 86 81 77 80 82 71 74 76 77 66 75 81 86 82 84 72 71 80 85 83 91 91 86 83 73 68 66 66 74 80

min 50 54 51 57 49 50 47 47 46 51 46 46 51 52 65 56 52 47 50 52 53 56 60 53 54 53 53 52 47 52 55

Climatological Data for Davis, California: May 1985 Soil Temperature Prec Evap 10cm 20cm 50cm max min max min mean totals 78 70 70 68 69 0 0.31 78 71 71 69 72 0 0.5 78 72 72 70 70 0 0.36 78 71 72 70 71 0 0.41 77 71 72 69 71 0 0.5 78 70 72 69 71 0 0.46 76 69 70 68 69 0 0.41 76 69 70 68 70 0 0.39 77 68 70 68 70 0 0.41 76 69 70 68 70 0 0.37 72 66 70 66 70 0.02 0.22 72 66 68 66 69 0 0.29 76 69 70 68 72 0 0.45 79 70 72 70 70 0 0.38 78 73 73 71 72 0 0.68 79 72 73 71 72 0 0.6 78 72 72 70 72 0 0.41 78 71 72 70 72 0 0.35 79 71 73 71 72 0 0.33 81 72 74 71 72 0 0.44 82 74 74 73 74 0 0.39 83 75 76 74 74 0 0.43 84 76 79 74 75 0 0.4 85 78 78 75 76 0 0.47 85 78 78 76 77 0 0.48 82 74 77 74 76 0 0.42 76 72 74 72 74 0 0.22 78 72 73 72 74 0 0.41 75 68 72 69 74 0.04 0.17 76 68 71 70 72 0 0.29 79 71 72 70 72 0 0.49

High Low Mean Total

93 64 80

57 40 47

91 66 78

65 46 52

85 72 78

Air Temperature 2m

15m

78 66 71

79 68 73

76 66 70

15

77 69 72

0.04 0 0 0.06

0.68 0.17 0.4 12.44

0.5m 51 88 126 121 127 195 199 120 103 146 77 93 109 98 240 195 109 83 89 117 86 100 111 123 132 310 35 204 87 63 158 310 35 126

Wind 2m 10m 2m passage direction 74 32 CALM 116 71 S 180 165 SW 161 109 N 173 158 N 266 266 SW 257 258 S 162 106 S 146 83 CALM 207 184 S 111 49 N 124 46 N 146 109 N 127 52 NW 311 352 NW 271 302 W 171 140 N 127 48 NW 119 39 N 152 70 CALM 116 41 CALM 133 43 CALM 138 78 S 163 105 CALM 175 111 SW 259 215 W 203 171 WSW 269 252 SW 134 87 CALM 94 38 NW 208 179 S 311 74 171

352 32 128

Table 7. Climatological Detail

Climatological Detail Statistical Category Growing degree days (base 50 F) Heating degree days (base 65 F) Cooling degree days (base 65 F) Days 90 F or above Days 32 F or below

April 374 106 30 1 0

May 417 92 44 2 0

Observations for 24 hr period ending at 8am; year 1985.

Temperature in Fahrenheit; precipitation and evaporation in inches Wind passage in statute miles; wind direction at 8am Data Source: NOAA Reference Climatological Station maintained by the Department of Land, Air and Water Resources, UC Davis.

Acknowledgements and Additional Comments Special thanks to: Kenneth Cassman, Ph.D., (Agronomy and Soil Science) at the University of California, Davis for comments and direction on this field study.

Vincent Rubatsky, Cooperative Extension Vegetable Crops, UC Davis for information on California lettuce production.

The Department of Land, Air and Water Resources at the University of California, Davis for climatological data.

Fertilizers. It may be pointed out that inferior yields from organic manure may have resulted from insufficient time for the material to break down, preventing the release of most of its nitrogen. The environmental impact and toxicity of chemicals should be taken into consideration.

In materials and methods, metric units should have been used for the plot size and NPK application was reported per plot which should have been converted to per ha basis.

16

References Cassman, K.G., et al., “An Economic Analysis of 1982 Soybean Production in Minya Governorate,” Food and Agriculture Organization, 1984.

Gardner, B.R., and Pew, W.D., “Comparison of Various Nitrogen Sources for the Fertilization of Winter-grown Head Lettuce,” Journal American Society of Horticultural Sciences 104 (4): 534-536, 1979.

NOAA Reference Climatological Station maintained by the Department of Land, Air and Water Resources, University of California, Davis UCAE (University of California Agricultural Extension), “Lettuce Production in the Imperial Valley,” Circular 135, 1978.

Williams, William A., “Management of Nonleguminous Green Manures to Improve the Infiltration Rate of an Irrigated Soil,” Soil Science Society of America Proceedings, Vol. 30, No. 5, September-October 1966, pp.

631-634.

17