Soil and fertiliser nitrogen performance indicators for irrigated cotton in Australia

Context. Current cotton industry nitrogen (N) performance indicators have been developed in a narrow geographic region and do not represent production in southern Queensland (SQld) and southern New South Wales (SNSW), Australia. Aims. To benchmark soil and fertiliser N use efficiency (NUE) in irrigated cotton crops in these production areas, and to determine whether the current industry benchmarks are relevant in these regions. Methods. Eight field experiments were conducted over three growing seasons on commercial farms in SQld and SNSW. Experiments applied rates of urea-N to fields using surface or overhead irrigation. Key results. The industry partial factor productivity for N and internal N use efficiency (iNUE) benchmarks were not suitable NUE targets for these experiments because of variations in soil types, background soil N and other constraints to crop yield. Crops grown with soil N alone accumulated crop N and lint yield at 75% and 79% of crops producing 95% of site maximum lint yield (Y95). At fertiliser rates producing Y95, apparent N budgeting indicated only 25-30% of the potentially available soil and fertiliser N was present in crop biomass and soil mineral N at the end of season. Conclusions. Improving fertiliser N efficiency in irrigated cotton will require an understanding of site-specific factors that influence N availability, crop N demand and the ability of the crop to produce lint from N accumulated in biomass. Implications. Further research is required to develop the understanding of regional factors that influence crop N performance for the industry to improve its NUE.