Management of nitrogen and sulphur fertiliser for improved bread wheat ( Triticum aestivum ) quality

A change from the use of fertilisers containing sulphur (S) to predominantly urea for supply of nitrogen (N) to wheat ( Triticum aestivum L.) crops, and the generally low S status of New Zealand soils has coincided with a decline in the quality of wheat flour. Increased farinograph dough work input (WI) and increased extensigraph resistance have emerged with current crop management practices. The dynamics of N and S uptake were studied in a factorial experiment with four commercial wheat cultivars known to differ in yield potential, grain N content, and dough rheological properties. Treatments consisted of three levels of N fertiliser (nil, early application of 150 kg N/ha in three splits, and 150 early + 100 kg N/ha applied at anthesis) and two S levels (nil and 50 kg S/ha at emergence). N fertiliser strongly increased N uptake in vegetative parts and grain. In contrast, there was little effect of S fertiliser on grain yield or grain N and S concentration or uptake. However, S fertiliser treatment did raise the level of S uptake in vegetative plant material. S treatment reduced the N: S ratio. However, N treatment consistently had a greater influence than S fertiliser on mixing requirement (WI and water absorption) and extensigraph tests. Opportunities to manage S nutrition during crop growth in order to influence dough or baking characteristics existed only under high N management. In this situation, there was a significant reduction in WI following S fertiliser application. Cultivar choice was the single best option for achieving the required flour characteristics. Flour from wheat cultivars ‘Monad’ and ‘Otane’ had strong dough rheological properties suggesting they were well suited to breadmaking. WI was higher in ‘Monad’ than ‘Otane’ even though grain S concentrations were lower. The differences in WI could partially be explained by their grain N: S composition. This was, in turn, influenced by the level of soil mineral N and sulphate.