Reducing losses of nitrogen from cotton rotation systems
Cotton is one of many agricultural industries heavily reliant on nitrogenous fertilizers and water storages to maintain high levels of production. Cotton-based farming systems are therefore labelled as potentially high-risk agricultural systems with respect to gases losses of nitrogen to the atmosphere, nitrate leaching which contribute to environmental pollution. The inefficient use of fertiliser applied nitrogen also reduces profitability. Concern has mounted in recent decades regarding the emission of greenhouse gases to the atmosphere through human activities. Modern agriculture has contributed to these emissions with the release of CO2 from soils during land clearing and annual tillage operations. Nitrous oxide (N2O) emissions are reportedly on the increase with the elevated use of nitrogenous fertilizers and irrigation in crop production systems. Reducing the potentially large N emissions from these cropping systems has therefore been widely identified as a high priority for increasing profitability and reducing environmental pollution and is directly related to improved water and nitrogen use efficiency. Our research has confirmed that management practices currently being promoted across the cotton industry are making a positive contribution to reducing greenhouse gas emissions from Australia soils. Experimental data has confirmed that typical seasonal on-farm emissions of the greenhouse gas, N2O, which is over 300 times more potent as CO2, from irrigated cotton systems in Australia and using split applications of nitrogen, are less than 1% of the total nitrogen applied. This figure is well below the default global average for emissions used by the Intergovernmental Panel for Climate Change (IPCC) in developing greenhouse gas inventories. The total loss of gaseous nitrogen using a typical split application (excluding ammonia) is estimated to be about 16%. The following Best Management Practices have been identified for reducing nitrogen losses and associated greenhouse gas emissions: • A reduction in the time between initial fertiliser application and planting is critical. • Increasing the amount of fertiliser N applied later in the season (relative to upfront applications), will potentially increase yields and increase the overall nitrogen use efficiency for the season. • Urea should be used in preference to NH3 in water run applications. • Green manures may substitute for mineral sources of nitrogen, however more work is required to confirm its utility as an alternative N source. Reducing greenhouse gas emissions requires an estimate of your on-farm emissions.