Soil water deficit effects on soil inorganic nitrogen in alternate-furrow flood irrigated Australian cotton production systems

Context . Predicting the nitrogen (N) mineralisation from soil organic matter is a key aid to fertiliser decision-making and improving the N fertiliser use ef fi ciency of a crop. Aims and methods . Field experiments were conducted to assess the amount of inorganic N derived from soil organic matter mineralisation over two seasons (2017 – 2018 and 2018 – 2019) across treatments differing in irrigation frequency and amount. During both seasons, the plant line soil in each treatment was sequentially sampled at each irrigation event. Key results . There was an effect of the soil water de fi cit on the measured accumulated soil inorganic N derived from mineralisation in both measurement years. It was observed that soil inorganic N accumulated in the plant line rather than in other hillside and furrow positions for all soil moisture de fi cit treatments in both years. In 2017 – 2018, N accumulated in the plant was signi fi cantly greater than the measured accumulated inorganic N (0 – 300 mm). Conclusions and implications . The sequential soil sampling approach was challenging in irrigated systems and we propose a hybrid measurement of pre-season available soil N and/or plant N uptake in nil N fertiliser plots as a means of estimating N derived from soil organic matter mineralisation. furrow-plant line-non-irrigated furrow transect. This paper examines variations in soil N mineralisation in various positions in the irrigated paddock plant-bed (hill) and furrow system under two contrasting soil water de fi cits in 2 years of cotton production. The irrigation frequencies relied on soil water measurements averaged across treatments reaching 50-mm and 70-mm de fi cit in the 2017 – 2018, and 60-mm and 90-mm de fi cit in the 2018 – 2019 season.