Reducing Nitrous Oxide Emissions from Sugarcane Land. Mackay, Queensland, 2009-2012 [Theme 5: Reducing emissions through improved NUE]

Australian sugarcane soils generally receive large amounts of N fertiliser each year, ranging from 120 to 200 kg N/ha. In combination with the wet and warm climate and cane trash retention on the soil surface, these soils provide exceptional conditions that favour N2O production. However, the contribution from the Australian sugar industry to the national greenhouse budget remains unclear due to inadequate year-long measurements with continuous or reasonably intensive sampling.

There is a need to investigate effective management practices to reduce the greenhouse signature from sugar industry. Recently, grain legume crop rotation and green cane trash blanketing have been considered promising management practices that can reduce the costs associated with fertiliser application and improve soil health and fertility. As legumes fix N from the atmosphere and supply N to the succeeding crop, the rate of fertiliser N application under legume rotation is generally much lower than under continuous sugarcane cropping. The effect of displacement of fertiliser N by biologically fixed N on greenhouse gas emissions associated with sugarcane farming remains to be investigated. In addition, many studies in temperate regions have shown that application of nitrification inhibitor into NH4+-type fertilisers and urea could reduce N2O emissions from N fertiliser by up to 50-60%. However, their effectiveness can be affected by soil temperature and biochemical properties, and field assessment in tropical and subtropical sugarcane farming systems are required.

In this study, N2O emissions from a representative sugarcane farm (near Mackay) are measured over 3 years using automatic and manual chambers. The objectives of this study are to:
(i) quantify annual N2O emissions from normal sugarcane farming under green cane trash blanketing;
(ii) determine whether use of leguminou rotation crops or application of nitrification inhibitor can reduce greenhouse gas emissions; and
(iii) improve understanding of the key factors that control N2O emissions from sugarcane soil.