The Australian Cotton industry in the last decade has enjoyed extraordinary growth in cotton lint yields, increasing from 2038 kg lint/ha in 2005 to 2610 kg lint/ha in 2015. Higher yields have been driven by both improved varieties and crop management strategies. One issue rising from the increase in yields is the recent industry trend of applying high rates of nitrogen (N) fertiliser to cotton crops. Industry audits are reporting many growers are applying in excess of 300 kg N/ha, in order to achieve yields greater than 2724 kg/ha, in spite of research suggesting these yields are achieve able with applied N rates of 220-250 kg N/ha.
To address the issue, two field experiments were conducted over two years on a commercial cotton farm in the Liverpool Plains of Northern NSW. Experiment treatments included varied N rates, with the aim to quantify research outcomes conducted within a research institute experiment. The investigation found N rate significantly impacted on cotton yield, NUE and the economic optimum N rate. On average there was a 7% increase in yield at every additional 50 kg N/ha increment from 150 to 300 kg N/ha (2552 to 3040 kg/ha of cotton lint).The economic optimum N rate was determined to be 237 kg N/ha over the two seasons. This trial was conducted within the Upper Namoi region of Northern NSW and thus optimum management systems should be developed for other regions that are specific to their growing environments.