An irrigated cotton farm emissions case study in NSW, Australia

The primary source of emissions in broadacre cropping is synthetic fertiliser applied to farmland, creating nitrous oxide from chemical processes in the soil. In high yielding irrigated cotton production, nitrogen remains a key input to maintain yields and maximise crop returns. This study aims to identify immediate strategies available to broadacre irrigation to reduce emissions and maintain profitability. Four emission mitigation strategies on a large broadacre irrigation farm in Northern New South Wales producing cereals, pulse and cotton crops were modelled. The results show rotating cotton with pulse crops, instead of wheat, can achieve an 8% reduction in emissions and increase whole farm gross margin by 12%, due primarily to the current historically high chickpea price and a reduction in applied nitrogen. Combining enhanced efficiency fertilisers in cotton crops in a more comprehensive abatement strategy has shown an indicative 13% emissions reduction from the baseline scenario, with a 6% reduction in farm gross margin from the increased fertiliser cost. However, uncertainty regarding the impact of EEFs on cotton yield in vertosol soils is noted. The soil sequestration from including a tree-lot in the emissions reduction strategy reduced whole farm emissions by 11% and reduced whole farm gross margin of 3%; however, difficulty in establishment and high establishment costs can add economic risk. Combining all three emissions reduction strategies results in a significant emissions reduction of 33% and a 4% gain in whole farm gross margin. Sensitivity analysis highlights gross margins results to be particularly sensitive to chickpea price movement. With this desktop modelling in mind, the discussion draws on industry research revealing that at a field scale, carefully balanced agronomic nuances exist between cotton cropping rotations and secure economic outcomes. The addition of achieving environmental objectives simultaneously with these variables is yet another future challenge facing government emissions abatement incentive programs and broadacre cropping businesses.