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Response of wheat to four nitrogen management systems

B.A. Kearsley, N. Cordon and H.A. Reimers

Department of Agricultural Technology, The University of Adelaide, Roseworthy SA 5371; Hifert, Port Lincoln SA 5606

Post-emergent application of nitrogen to wheat crops has been recommended as a means of increasing grain and protein yields in wheat crops on the Eyre Peninsula of South Australia. However, responses are dependent upon seasonal conditions, in particular rainfall in the latter part of the growing season. Farmers have available to them several commercial analysis kits to predict the need for nitrogen application in the growing crop. This paper reports on results of using these kits at farm level and the resultant economic advantage.

Methods

A comparison was made between two wheat crops grown in paddocks with different cropping histories at Yeelanna in South Australia. The first paddock had been a subclover (Trifolium subterraneum)/annual medic (Medicago truncutala) based pasture in the previous year and was sown to Molineux; the second had grown beans (Viciafaba cv. Fiord) and was sown to Spear. The four nitrogen management tools used were: the South Australian Department of Agricul- ture's Soil and Plant Analysis Service (SASPAS); Hifert fertiliser company's Nitraquick test kit; Top Fertiliser's Farm lab; traditional visual appraisal based on paddock history. Each of these methods was used to estimate the crops' nitrogen status and then the recommended rate of granulated urea was applied to unreplicated plots of 25 x 500 m. Measurements were made of tiller number, grain yield, grain protein and grain best weight. In addition, an economic analysis was carried out to estimate the most profitable of the treatments.

Results and discussion

Table 1. Grain yield, protein %, test weight and gross margin of treatments in each paddock.

The SASPAS testing service recommendation resulted in a higher gross margin than the traditional appraisal in both paddocks. Results obtained using the Farm lab and Nitraquick tests were variable. Traditional appraisal resulted in the lowest grain yields in each paddock and yet the economic returns were not the lowest of the treatments. Costs of production for the traditional appraisal were lower because the farmer decided, in each case, not to apply urea. Results of this trial clearly indicate the danger of relying upon measurements of a testing service without having access to local expertise for interpretation.

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