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Comparing grain yield and protein from pre-plant and at-sowing N application to cereal crops

D. W. Lester and C. W. Dowling

Incitec Fertilizers, P.O. Box 623, Toowoomba Qld.

ABSTRACT

Frequent discussion occurs within the grain growing community regarding the relative merits of different nitrogen (N) fertiliser application timings. An experiment was conducted to compare grain yield and grain protein % resulting from pre-plant (PP) or at-sowing (AS), banded applications of urea over a number of different cropping seasons at the same site. Results from each of 4 cereal crops indicate no significant difference in grain yield or protein % at either N application timing.

KEYWORDS

Nitrogen fertiliser, grain, protein, wheat, sorghum, yield.

INTRODUCTION

Application of N Fertilizers is now standard practice for the majority of cereal grain producers in the northern grain belt of eastern Australia. Much research has been conducted to investigate optimum rates of N fertiliser in cereal crops (Holford et al. 1992, Strong et al. 1996), use of N in different cereal production tillage systems (Strong 1996), and recovery of N fertiliser applied at different times and depths (Strong et al. 1992).

Strong and Cooper (1992) reported on a series of experiments conducted during 1978, 1981 and 1982 using different N application times for wheat and sorghum, however this work was influenced by relatively dry fallow and growing periods, which influenced the crop response to N.

Since 1996, the "Colonsay" long-term fertiliser experiment in the Formartin district on the Darling Downs has included treatments comparing the performance of PP and AS application at four N rates.

MATERIALS AND METHODS

The experiment consists of a factorial combination of 4 N rates (0, 40, 80, 120 kg/ha/crop), applied either PP or AS, at 4 P rates (0, 10, 15, 20 kg/ha/crop). N is applied as urea (46% N) and P as triple superphosphate (20.7% P). A randomised block design with three replicates is used. Urea applied at-sowing is banded 5 cm to the side of the seed row. The soil is a black vertosol with pH (CaCl2) 7.8, CEC (cmol+/kg-1) 57, Leco C 1.35%, Leco N 0.08%.

Four cereal crops have been produced since 1996, wheat (Triticum aestivum cv. Cunningham) in 1996, grain sorghum (Sorghum bicolor Moench cv. Pacific Seeds "MR-Buster") in 1997/98, grain sorghum (Sorghum bicolor Moench cv. Pioneer Seeds "Magnum MR") in 1998/99 and 1999/2000.

Pre-plant N applications were carried out 103 days before sowing (DBS) in 1996, 67 DBS in 1997/98, 48 DBS in 1998/99, and 165 DBS in 1999/2000. The same equipment and tines were used to apply fertiliser PP and AS. At-sowing plots were tilled when pre-plant N was applied to maintain tillage equivalence between treatments.

Grain yields and grain N concentrations were measured from all plots in all years. After gravimetric determination of grain water content, grain yield and protein were adjusted to 12% moisture. Grains were analysed for N concentration in Kjeldahl digests using automated ammonium-N analysis. Grain protein concentration was calculated by multiplying grain N concentration by 5.7 for wheat and 6.25 for sorghum

RESULTS and DISCUSSION

Grain yield (Fig 1a) and grain protein (Fig 1b) were not affected by N timing in any of the 4 crops. Data shown are the means of the 4 N rates for 4 P rates. N application rate was significant for each crop, the maximum grain yield increase from N was 1783 kg/ha in 1996, 166 kg/ha for 1997/98, 3092 kg/ha for 1998/99 and 3780 kg/ha for 1999/2000. Maximum protein increase was 3.3% in 1996, 1997/98, and 1998/99, and 4.2% in 1999/2000.

Figure 1. Comparing pre-plant and at-sowing nitrogen applications over four crops for (a) grain yield and (b) grain protein.

The lack of difference between PP and AS applications, as indicated by crop response suggests a number of scenarios between environmental parameters (soil moisture and temperature) and N (soil and fertiliser).

Pre-plant applications for the 4 crops were between the months of March and September, during drier months in northern Australia (median March-September 219 mm cf annual median 643 mm). Rainfall received between applications and sowing was 245 mm in 1996, 86 mm in 1997/98, 160 mm in 1998/99, and 173 mm in 1999/2000. During these seasons of below median or median rainfalls when soil temperatures (Havlin et al. 1999) are in decline there is low probability of losing N due to denitrification, a process that was shown to reduce the effectiveness of N applied in wetter summer months (Strong and Cooper 1992).

Crops accessed similar quantities of N applied AS as for N applied PP, suggesting that for these crops the effectiveness of N applied at sowing was not reduced due to it being stranded in dry topsoil.

CONCLUSIONS

Similarity of responses to N applied PP and AS, where N was in limited supply, suggest negligible difference in the efficacy of N applied up to 165 days before sowing during periods of low rainfall when soil temperatures are in decline. Where there is low probability of N loss from PP application soil conditions, moisture conservation, labour availability and factors other than potential loss should be the prime determinants of N timing.

ACKNOWLEDGMENTS

The continued support of Noel and Jenny Peters on whose property "Colonsay", this research is conducted is gratefully acknowledged.

REFERENCES

1. Havlin, J.L., Beaton, J.D., Tisdale, S.L., and Nelson, W.L. 1999. In: Soil Fertility and Fertilizers. 6th Ed. (Prentice Hall: Upper Saddle River, New Jersey). pp. 128.

2. Holford, I.C.R., Doyle, A.D., and Leckie, C.C. (1992) Aust. J. Agric. Res. 43, 969-86.

3. Strong, W.M. and Cooper, J.E. 1992. Aust. J. Soil Res. 30, 695-709.

4. Strong, W.M., Saffigna. P.G., Cooper, J.E., and Cogle, A.L. 1992. Aust. J. Soil Res. 30, 711-21.

5. Strong, W.M., Dalal, R.C., Weston, R.J., Cooper, J.E., Lehane, K.J., King, A.J., and Chicken, C.J. 1996. Aust. J. Exp. Agric. 36, 665-74.

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