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Yield and protein benefits from application of nitrogen fertiliser to wheat on upper Eyre Peninsula

Jon Hancock1, Dr Bob Holloway1, Dr Annie McNeill2 and Dr Glenn McDonald3

1SARDI, Minnipa Agricultural Centre, PO Box 34, Minnipa, SA 5654 www.sardi.sa.gov.au Email hancock.jonathan@saugov.sa.gov.au; holloway.bob@saugov.sa.gov.au
2
University of Adelaide, Department of Agronomy and Farming Systems, Roseworthy Campus, Roseworthy, SA 5371 www.adelaide.edu.au Email ann.mcneill@adelaide.edu.au
3
University of Adelaide, Department of Plant Science, Waite Campus, Glen Osmond SA 5064
www.adelaide.edu.au
Email glenn.mcdonald@adelaide.edu.au

Abstract

Replicated field trials were established in 2001 to examine the responses to nitrogen (N) fertiliser in wheat on two important soil types of the upper Eyre Peninsula. Three experiments were conducted at sites with grey calcareous soil and one at a site with a sand over clay. The effects of different rates and forms of N applied in conjunction with different forms of phosphorus (P) fertiliser on the grey calcareous soils and the effects of N rate, depth of placement and late N applications on a sand over clay were investigated. On the grey calcareous soils, responses to N were greatest when P limitations were reduced by using fluid fertiliser. Applying N deep in the profile followed by broadcast applications of N later in the season resulted in substantial yield and protein improvements on the duplex soil. The results indicate that there is potential to improve N responses in the region by fertiliser management.

Key Words

Nitrogen Phosphorus Calcareous Eyre Peninsula Wheat

Introduction

The grain yields of wheat in the low rainfall areas of the upper Eyre Peninsula are generally low and the nitrogen (N) requirements of these crops have traditionally been satisfied through biological fixation from a medic pasture phase. Farmers have applied little or no N fertiliser to their wheat crops, but recent work on improving the form and placement of N and phosphorus (P) fertiliser may mean that the use of N fertiliser should be re-examined. On the grey calcareous sandy loams substantial increases in yield can be achieved by using fluid phosphorus fertiliser (Holloway et. al., 2001). Correcting the chronic P deficiency in the region may improve the responsiveness to N fertiliser. On a duplex soil, Doudle et al. (2001) found that deep (40 cm) placement of N and other nutrients throughout the sandy A horizon increased yields significantly. However the practicalities of placing N deep in the soil could limit the uptake of this research on farm, unless the benefits are considerable. This study evaluated the responses to N fertiliser when applied with or without adequate sources of P to grey calcareous soils on upper Eyre Peninsula and investigated different options for improving the N status, grain yield and protein of wheat grown on sand over clay.

Methods

N and P Interaction Trials

Wheat (cv. Frame at Miltaburra and cv. Yitpi at Yandra and Warramboo) was sown at 62 kg/ha in a fully randomised block design with 4 reps. Three rates of N, as urea (0, 15 and 30 kg N/ha) were applied below the seed in either granular or fluid form. Two rates of P (0 or 15 kg P/ha) were also applied below the seed in either granular (triple superphosphate, 20%P) or fluid (phosphoric acid based, 27%P w/w) form. A post-emergent foliar spray containing zinc sulphate, copper sulphate and manganese sulphate at 1.5, 0.2 and 2 kg/ha of the element respectively was applied.

N Application Technique Trial

A trial was established at Wharminda where approximately 40 cm of sand overlays clay. A nutrient blend was injected throughout the sand layer with a paraplow on May 4. The blend contained P, K, S, Cu, Mn and Zn applied at rates of 20, 25, 12.8, 4, 10 and 10 kg/ha of the element respectively. N was applied at three rates (0, 15 or 60 kg N/ha) either as dissolved urea at the beginning of the season or in a 2:1 split application of dissolved urea at the beginning of the season and broadcast urea 79 days after sowing. The initial N application was either distributed throughout the top 40 cm of the sand layer (deep) with the paraplow or applied 5 to 10 cm below the soil surface (shallow) during the seeding operation. Wheat, cv. Yitpi was sown at 70 kg/ha with triple superphosphate + 5% Zn at 50 kg/ha beneath the seed.

Soil and plant sampling and analysis

Soil samples were taken from each trial prior to sowing to determine the initial N status. Plant samples were collected at tillering and anthesis, dried at 60C for 48 h and weighed. At maturity fertile tiller numbers were counted, the samples weighed and threshed. Rooting depth and root length density were measured in the N application technique trial during September. Plots were harvested at maturity and grain samples were retained to measure screenings and grain protein concentration. The total amount of N removed in the grain was derived and the agronomic efficiency of fertiliser N uptake was calculated using the N difference method of Craswell and Godwin, 1984.

Results

N and P Interaction Trials

At Miltaburra growing season rainfall was average and there was relatively high initial mineral N in the profile (Table 1). Crop emergence and growth through the season were unaffected by the application of N or P except for a small increase in total crop biomass, yield, grain protein and screenings following the addition of 15 kg N/ha (Table 2).

Table 1: Initial soil N, Colwell P, and April-October rainfall for each site

 

Miltaburra

Yandra

Warramboo

Wharminda

Initial Nitrate N (mg/kg) 0-30 cm

74

44

47

11

30-60 cm

     

16

Colwell P (mg/kg) 0-10 cm

32

25

26

15

April-October rainfall (mm) 2001

236

354

314

187

Average

236

298

 

215

Table 2: Influence of applied N on yield, grain quality and economic return at Miltaburra in 2001.

N Rate

DM at maturity (kg/ha)

Grain Yield (kg/ha)

Protein
(%)

Screenings
(%)

N Removed in Grain
(kg/ha)

Agronomic Efficiency
(kg grain / kg N)

Nil

3099

1503

12.8

2.3

34.4

-

15 kg/ha

3375

1580

12.9

2.4

36.4

5.12

30 kg/ha

3293

1520

13.0

2.4

35.3

1.57

LSD (P<0.05)

202

72

0.1

0.1

1.7

3.33

At Yandra, the application of both N and P increased crop growth and produced large grain yield increases (Table 3). Tiller number was increased by adding P (nil = 125, granular = 134 and fluid = 147 tillers/m2) and N (nil = 120, 15 or 30 kg/ha = 143 tillers/m2). Grain yield increased with increasing rates of N and there was a significant yield advantage through the use of fluid P rather than granular P. Mean grain protein concentration and screenings concentrations were 10.8% and 0.6% respectively and were not affected by any treatment.

Table 3: Influence of N rate and source of P on the grain yield (kg/ha) of wheat (lsd=124) and N content (lsd=2.4) at Yandra


N Rate

P Source

None

Granular

Fluid

Grain Yield

Grain N

Grain Yield

Grain N

Grain Yield

Grain N

Nil

1578

30.7

1681

33.0

1721

33.2

15 kg/ha

1708

33.1

2077

40.2

2213

42.7

30 kg/ha

1760

34.0

2264

43.5

2421

46.8

At Warramboo, crop growth was improved by applying P, particularly when applied in fluid form. The benefits of P nutrition were most pronounced early in the season. At tillering, applying fluid P increased growth by 37% compared to the granular P treatments and by 113% compared to nil P. The difference between fluid and granular P was reduced to 12% by anthesis and 6% by harvest. Tiller number was greatly increased by P nutrition. The addition of N did not affect tiller production or crop growth before anthesis but increased grain yield when applied with P (Table 4). Grain protein levels were increased by using fluid or granular P (Table 4) and with increasing rates of N. Up to 50 kg N/ha was removed when P and N were both applied (Table 5) although a large proportion of this is likely to have come from the soil since 38 kg N/ha was removed in the nil treatment. Agronomic efficiency was relatively poor overall and declined at the higher N rate (Table 5). In the absence of P fertiliser, applying N caused a reduction in grain yield (Table 4), and a negative agronomic efficiency.

Table 4: Influence of N rate and P source on the yield (kg/ha) and grain protein (%) of wheat at Warramboo

N Rate

No P

Granular P

Fluid P

Average
(lsd = 128)

 

Grain yield

 

Nil

2081

2446

2550

2359

15 kg/ha

2003

2633

2783

2473

30 kg/ha

1796

2483

2680

2320

Average (LSD = 221)

1960

2521

2671

2384

 

Grain protein concentration

 

Nil

10.3

10.3

9.8

10.2

15 kg/ha

10.9

10.7

10.3

10.6

30 kg/ha

11.2

11.0

10.6

10.9

Average (LSD = 0.5)

10.8

10.7

10.3

10.6

         

Table 5: Influence of N rate and P source on N removal in wheat grain (kg/ha) and the agronomic efficiency (kg gain/kg N fertiliser) at Warramboo

N Rate

No P

Granular P

Fluid P

 

N removal

Nil

37.76

44.30

44.14

15 kg/ha

38.19

49.17

50.23

30 kg/ha

35.25

47.73

50.22

LSD=4.25

     
 

Agronomic efficiency

15 kg/ha

-5.2

12.5

15.5

30 kg/ha

-9.5

1.2

4.3

Average (LSD = 8.6)

-7.3

6.9

9.9

Wharminda N Technique Trial 2001

The growing season at Wharminda was slightly drier than average (Table 1). Increased rates of fertiliser increased dry matter at tillering, regardless of the application method (Table 6). Root measurements (data not shown) taken prior to anthesis showed that root growth beyond 10 cm was encouraged by deep N placement and high N rates. Plant biomass at anthesis was mainly influenced by the amount of N added rather than the depth of application. The main benefits of subsoil nutrition and of late N applications became apparent towards harvest where a combination of 40 kg of N applied to the subsoil in addition to 20 kg of N broadcast at late tillering produced the highest yields (Table 6). Grain protein was relatively unaffected by the depth of N placement but was increased by the higher N rate and responded well to the late N applications. The amount of N removed in the grain and agronomic efficiency also increased with late N applications.

Table 6: Influence of treatments on crop growth, grain yield, quality, N removal and agronomic efficiency of wheat at Wharminda.

Depth and N rate
(kg/ha)

Dry matter (kg/ha)

Grain Yield

Protein

Screenings

Grain N removal

Ag. eff.

 

Tiller

Anth.

Mat.

(t/ha)

(%)

(%)

(kg/ha)

(kg/kg)

Nil

311

3111

5028

1.69

8.9

1.0

26.6

 

15 Shallow

428

3730

6259

1.71

9.0

1.2

27.3

1

10 Shallow + 5 Late

371

3483

5015

1.91

9.6

1.2

32.4

14

15 Deep

436

3594

5777

2.00

8.7

1.2

31.2

20

10 Deep + 5 Late

383

3524

6653

2.20

9.0

1.1

34.9

33

60 Shallow

483

3867

5783

1.98

9.0

1.2

31.8

6

40 Shallow + 20 Late

470

3614

6643

2.09

11.4

1.6

42.9

8

60 Deep

532

4325

7581

2.24

9.7

1.6

38.8

11

40 Deep + 20 Late

397

4775

6830

2.53

10.9

1.5

49.3

15

LSD

121

827

1272

0.25

0.3

0.3

3.9

15

Conclusions

On the grey calcareous soils, correcting P deficiency was a critical factor determining the response to N. On the duplex soil at Wharminda, high rates of N, distribution into the subsoil and an application of N at late tillering all contributed to improving crop yield and grain protein.

Acknowledgements

Leon & Marilyn Mudge, Ian & Gladys Morgan, Tim & Tracy VanLoon and John Masters for the provision of trial sites. Penny Day and staff of Minnipa Agricultural Centre who gave input and technical assistance. This research was supported by the South Australian Grains Industry Trust Fund and the Grains Research and Development Corporation.

References

(1) Craswell, E.T. and Godwin, D.C. (1984) Advances in Plant Nutrition, 1:1-55

(2) Doudle, S.L. (2000) Eyre Peninsula Farming Systems 2000 Summary, 100-101.

(3) Holloway, R.E., Bertrand, I., Frischke, A.J., Brace, D.M., McLaughlin, M.J., Shepperd, W.P. (2001) Plant and Soil, 236:209-219.

(4) van Herwaarden, A.F., Farquhar, G.D., Angus, J.F. and Richards, R.A. (1998) Aust. J. Agric. Res., 49:1067-81

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