The majority of Australia’s cotton producing soil is grey or black vertosols which have high clay content and are naturally prone to waterlogging following heavy rain or surface irrigation. Waterlogging events can lead to the loss of the excess applied nitrogen, these losses have been reported to be up to 50-100 kg N/ha (Rochester, 2003). Cotton (Gossypium hirsutum) production in Australian relies heavily on the application of irrigation water, and therefore there are many possible events for large nitrogen losses within a single growing season. Poor irrigation management or old inefficient irrigation infrastructure would also increase the potential nitrogen lost from an irrigation system. Janat (2008) found that modern irrigation application methods (such as drip irrigation) could improve Water Use Efficiency (WUE) by up to 30%.

The findings of this project showed that cotton management strategies influence the nitrogen cycle within an irrigated cotton system. Management options such as switching the furrow that is irrigated, the volume of water applied during an irrigation event and optimising nitrogen and water application, influenced the crop uptake of nitrogen and the amount of nitrogen (and its associated gases, such as nitrous oxide) lost from the system. Of the 36 kg N/ha that was lost from irrigation tail water through the cotton season 50% was lost at the first irrigation event. Developing strategies and best management practices (BMP) to reduce the effect of the first irrigation would have a significant impact on reducing the emissions from an irrigated cotton farm.

The agronomic management options that were investigated in this project could be applied with little to no impact on the farming operation. Such as irrigating down the furrow that had the fertiliser direct drilled and increasing the volume of applied water in the first irrigation event. These management options reduced the nitrogen lost in the tail water (up to 50%), while importantly had no impact on farm productivity (cotton yield).