The greenhouse effect is widely considered one of the major threats to Australia agriculture. There is increasing evidence that carbon dioxide, methane and nitrous oxide concentrations are reaching levels that will cause a significant warming of the earth’s atmosphere over the next 10 to 100 years causing great changes in seasonal weather patterns. Forecasts in Australia suggest a reduction in rainfall in the interior regions and increased incidence of drought. If a concerted effort is made to reduce global greenhouse gas emissions, these changes can possibly be avoided.

Cotton is one of many agricultural industries heavily reliant on nitrogenous fertilizers to maintain high levels of production. The inclusion of legumes also provides a boost to the nitrogen economy of the system. Surplus nitrogen is a direct contributor to nitrous oxide (N2O) emissions which has a Global Warming Potential (GWP) approximately 300 times that of a single molecule of carbon dioxide (CO2). Reducing N2O emissions from cropping systems has been widely identified as the highest priority in greenhouse gas abatement in crop production and for ensuring profitability through enhance N and water use efficiency.

The project is the first dedicated analysis of greenhouse gas emissions from soils in cotton based farming systems and its relationship to sustainable cropping practices. Field based estimates of greenhouse gas emissions, specifically nitrous oxide, from an alkaline grey clay under cotton receiving up to 200 kg N/ha of fertiliser, ranged from 0.5 – 2.2 kg N/ha during the 10 week period after the first irrigation. On average only 0.35% of the nitrogen applied as fertiliser was emitted as N2O, which is low compared to global estimates of emissions from fertilisers. Emissions increased to over 1.5% of applied nitrogen when 300 kg N/ha was added, which surpasses the IPCC’s estimated value of 1.25% for deriving N2O emissions from fertiliser sources. Laboratory and simulation studies carried out within this project indicate N2O emissions equivalent to 3% of applied fertiliser nitrogen for a range of clay soils from across the industry.

More field data is urgently needed to ensure current and future management practices are tailored to minimise emissions and maximise nitrogen and water use efficiency. A continued shift to sustainable farming practices, reductions in fallow periods and rotation crops will provide a win-win situation to the cotton and associated industries. This will include enhanced carbon sequestration (and fertility) of soils and a significant reduction in the amount of nitrogen fertiliser which is left unused in the soil profile and potentially lost to the atmosphere as nitrous oxide. More efficient nitrogen management will reduce emissions and increase profitability whilst contributing to the abatement of climate change and its impact on Australian agricultural systems.