Long term nitrogen management for sustainable farming systems in south west NSW

2020

Long term nitrogen management for sustainable farming systems in south west NSW Authors: Michael Moodie1 Research Team: Todd McDonald, Chris Davies 1 Frontier Farming Systems Funded By: Western Local Land Services (WLLS) Project Title: Local Land Services Partnership Peer Review: Tanja Morgan (MSF) Key Words: Nitrogen, Soil N supply, crop N demand, N balance, legume, low rainfall

Key Messages ● ● ●

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Legumes produced 3-3.5 t/ha of dry matter and lentils yielded 1.6 t/ha. The oaten hay treatment produced 4.7 t/ha of dry matter.

Barley responded to increasing N fertiliser inputs, however the yield benefit per unit of N was small (5 kg grain/kg N). Wheat did not respond significantly to fertiliser N inputs.

Low output legumes contributed the highest net N inputs with 95 kg N/ha provided by vetch brown manure treatment. Vetch hay and lentil treatments both had a small N balance of around 15 kg N/ha after accounting for N removed in the hay and grain.

Fertiliser N rates of 50-70 kg N/ha were required to maintain the N balance in cereal crops.

Background The cropping region in South Western NSW has evolved dramatically in the last several decades. Traditionally cropping practices were highly conservative with one-two seasons of mechanical fallow between cereal crop phases before these rotations moved towards continuous cropping with cereal crops during the 2000’s. This led to major gains in water use efficiency and environmental benefits from improvements in groundcover, however this system was not sustainable with the eventual development of agronomic issues such as brome grass and declining fertility.

Over the past decade, there has been a further refinement in paddock rotations with the adoption of more diverse rotations. Legume crops such as lentils, chickpea, field pea and vetch have become an important component of regional crop sequences and the added nitrogen (N) supply from these enterprises is providing significant vigour and yield benefits to subsequent cereal crops.

Despite the obvious benefits from improved N supply, most farmers are reluctant to apply additional N inputs from inorganic fertiliser inputs. Therefore, the question remains – can further productivity gains be achieved, particularly in better rainfall seasons, with improved N supply over and above what is supplied through the organic N sources from legumes. Furthermore, while pulse crops can fix considerable quantities of N, significant quantities of N are also removed as hay and grain. Therefore, additional N fertiliser inputs may be required to prevent N being mined from the soil organic N pool.

In 2020, a new trial was established near Gol Gol in the South Western NSW Mallee region with funding from the Western Local Land Services. This trial will run over three years to compare rotations with differing levels of N supply and inputs. In the subsequent season the break phase will be followed by a sequence of wheat and barley, with varying levels of fertiliser inputs overlayed.

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About the trial The trial site is located at Gol Gol in South Western NSW. The site has a sandy and alkaline soil with key properties shown in Table 1. The previous crop at the site was chickpea (which were droughted) and there was 90 kg/ha of soil N prior to sowing in 2020. Soil organic carbon and organic N stocks were also measured prior to the implementation of treatments (Table 2). This sampling determined that there were 2.4 t/ha of organic carbon and 0.7 t/ha of organic N in the top 30 cm of soil at the site.

Table 1.Key soil properties at the site

Treatmen t

Mineral N (kg/ha)

Phosphoru s (Colwell)

PB I

Sulphu r (KCL)

pH (CaCl2)

Salinity (EC 1:5)

Boro n (Hot)

Clay (%)

San d (%)

Silt (%)

61

5.9

7.6

0.13

1.7

70.0

25

8.4

7.9

0.13

1.8

28

6.7

8.1

0.16

2.6

17

7.9

8.4

0.34

11.0

15

15.3

8.4

0.42

19.7

19.

3 25.

7 35.

3 34.

3 36.

6

11.

3 10.

0 15.

3 18.

0 17.

6

9 0-10

32

10-30 30-60 60-90 90-120

64.7 49.3 48.3 46.0

Table 2.Baseline organic carbon and organic N stocks in the top 30cm

Treatment Organic Carbon (kg/ha) Organic Nitrogen (kg/ha)

0-10c m

10-30c m

977 238

1430 495

Total (0-30cm) 2400 733

The site is divided into three sub trials with each to be planted to a different phase of a three-year rotation in each season (Table 3). Within the wheat and barley phases four different N rates are applied: 10, 30, 50, 70 kg N/ha.

The site was sown on the 3rd of May in 2020 which was soon after the break of the season where 15mm of rainfall fell on the 29-30th of April. All crops received starter fertiliser: legume crops (Vetch, Lentil, Medic) received Granulock Z at 48.7 kg/ha while cereal crops (Wheat, Barley Oats) received DAP S Z at 62.5 kg/ha. Urea was applied as a top-dress application on the 12th of June to the wheat and barley treatments where additional N above starter fertiliser rate was required (e.g. 30, 50 and 70 kg N/ha). However minimal rainfall fell at the site during June and July and this possibly impeded crop uptake of the urea during this period. In-crop weeds, pests and diseases were managed with crop specific applications of pesticides throughout the season.

Table 3.2020 crops and varieties for each phase of the rotation

Phase 1

Phase 2

Phase 3

Wheat (Scepter)

Barley (Sparticus)

Lentil (PBA Highland XT) Vetch Hay (Timok) Vetch Brown Manure (Timok) Medic Pasture (PM250) Oaten Hay (King bale) Chemical Fallow

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Results & Discussion Break Crop Phase All break crops grew well in 2020 thanks to a timely opening break and favourable spring conditions. Legumes produced 3 – 3.5 t/ha of dry matter while lentil grain yield was 1.6 t/ha (Table 4). Oats produced 50% more dry matter than the legume treatments (4.7 t/ha) (Table 4). The N yield of lentil, medic and pasture was 60 kg/ha while the total quantity of N in the vetch dry matter was 90 kg/ha.

Table 4.Dry matter production and grain yield for treatment in the break crop phase. Samples were analysed for total N which was used to calculate the N yield for each treatment.

Phase 1 Lentil Vetch Hay Vetch Brown Manure Medic Pasture Oaten Hay

Dry Matter (kg/ha)

% N

Dry Matter N Yield Kg/ha

3060 3457 3447

2.0

2.6 2.6

61 90 89

2908 4701

2.1 1.3

62 62

Grain Yield

% N

Grain N Yield Kg/ha

1580

4.2

66

Chemical Fallow

Cereal Phase As 2020 was the first establishment year, there were no background rotation treatments, therefore both the wheat and barley phase trials only compared the rate response to N fertiliser. In the barley phase there was a significant response to increasing rates of N with 5 kg/ha more grain per 1 kg/ha of N fertiliser applied (Figure 1). For wheat there was also a positive trend of 3 kg/ha more grain per 1 kg/ha of N fertiliser applied, however this was not statistically significant (Figure 1).

Figure 1. Barley and wheat grain yield response to N rates

Nitrogen application also affected grain quality in barley but not in wheat (Table 5 and 6). Grain protein was increased significantly by the 70 kg N/ha rate. However, this rate also led to a slight increase in screenings and lower test weight compared to the other N treatments.

Page 4 Table 5.Barley grain quality parameters in for each N rate.

10 kg N/ha 11.6

30 kg N/ha 12.3

50 kg N/ha 12.4

70 kg N/ha 13.8

p value 0.0

LSD

1000 grain weight (g) Test weight (kg/HL)

40.2

40.5

40.8

40.1

0.6

n.s.

74.1

74.0

73.7

74.0

0.5

n.s.

Screenings (%)

1.6

2.4

2.6

3.9

0.0

1.0

Retention (%)

94.5

93.0

93.1

90.3

0.0

2.8

Treatment Protein (%)

1.3

Table 6.Wheat grain quality parameters in for each N rate.

Treatment

10 kg N/ha

30 kg N/ha

50 kg N/ha

70 kg N/ha

p value

LSD

Protein (%)

10.5

10.6

10.9

11.5

0.2

n.s.

48.7

48.4

48.8

48.7

0.8

n.s.

81.6

81.7

81.5

81.4

0.8

n.s.

1.2

1.1

1.1

1.1

0.7

n.s.

1000 grain weight (g) Test weight (kg/HL) Screenings (%)

Implications for commercial practice Although this was the first season of trials at the site, there are already large differences between treatments in terms of the N balance (N imports v exports). In the break crop phase lentil grain and vetch hay provided a slightly positive N balance of approximately 15 kg N/ha after estimating N fixation in the roots and shoots and accounting for large quantities of N (lentil 60 kg N/ha; vetch hay 90 kg N/ha) removed in the hay and grain. In contrast the low output legume systems of vetch brown manure and medic pasture contributed a positive N balance of 100 kg/ha and 80 kg/ha respectively. Oaten hay removed 60 kg N/ha.

Higher rates of N fertiliser were required to maintain N balance in the barley and wheat trials (Figure 2). The 70 kg/ha N fertiliser rate provided a neutral N balance in the barley trial while the 50 kg/ha fertiliser N rate balanced N inputs with N exports in the wheat. Supplying less than 50 kg N/ha as fertiliser led to the negative N balances of up to 44 kg N/ha (Figure 2).

This trial will continue for at least two more seasons where fertiliser N inputs will be overlayed on the rotational strategies. This will provide us with a more complete picture of the most sustainable methods of managing N across rotation using a combination of fixed N and fertiliser N inputs.

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Figure 2. Nitrogen balance (fertiliser N inputs – grain N export) for each N treatments barley and wheat phase trials

Acknowledgements The ‘Sustainable implementation of no-till farming systems’ project has been funded by the Regional Land Partnerships Program with NSW Local Land Services.

Thank you to the Linklater Family (Ian, Daniel and James) for providing land for this long-term trial.