Nutrition of irrigated crops on an alkaline brown clay soil at Trangie, New South Wales. 2. Wheat

Abstract

In a field nutrient-omission experiment, nitrogen, phosphorus, potassium, sulfur and zinc were sequentially omitted from a 'complete' fertiliser applied to irrigated wheat on an alkaline brown clay soil. Wheat forage and grain yields were recorded for 3 years following this single application. The chemical composition of forage and grain was determined. A second experiment elucidated the response to nitrogen fertiliser after 2 years of wheat or fallow. Deficiencies of phosphorus and nitrogen were evident in the second and subsequent crops. Forage and grain yields were reduced in the absence of these elements as were the respective concentrations of phosphorus and nitrogen in the forage and grain. The omission of zinc fertiliser reduced the concentration of zinc in the grain but not the grain yield. Omitting sulfur led to lower grain yields in the second year. Both sulfur and nitrogen were required to achieve maximum grain nitrogen and sulfur contents. The response to nitrogen fertiliser peaked at 130 kg/ha N after a fallow. After continuous wheat, however, over 200 kg/ha N was required for maximum yields. A positive tillering response to nitrogen accounted for much of this grain yield response. Grain nitrogen contents remained low until 100kg/ha N was applied.