Effect of nitrogen fertilizer management and waterlogging on nitrous oxide emission from subtropical sugarcane soils

Considerable potential for N2O emission from Australian sugarcane systems exists from high N fertilizer application rates and periodic waterlogging. To determine N2O emissions, 2 experiments were conducted on ratooned sugarcane grown under field conditions. In the first experiment, crops received 0, 100 or 200 kg N ha−1 as single or split application. In the second experiment, a sub-set of the single N application plots was subjected to waterlogging. Higher N2O emissions (350 μg–17 mg N2O m−2 h−1) occurred during warm and wet months (November–February) and coincided with high availability of mineral N in top soil (10–500 mg N kg−1 soil). Lower emissions (<350 μg N2O m−2 h−1) were detected in cool and dry months (March–October) coinciding with availability of low mineral N (<10 mg N kg−1 soil). Regression analysis showed significant positive correlations between N2O emissions and soil temperature, water-filled pore space and mineral N (ammonium and nitrate) content. N2O emissions, soil mineral N content and crop yield followed N application rates (0 < 100 < 200 kg N ha−1) and waterlogging amplified N2O emission. Split application of N fertilizer reduced annual N2O emissions in the 200 kg N ha−1 treatment. We estimate, using the IPCC Tier 1 approach that between 1.0% and 6.7% of applied N fertilizer was emitted as N2O. Our study demonstrates that immediate reduction of N2O emissions can be achieved by avoiding high levels of soil mineral N pools and waterlogging through appropriate fertilizer rates and time of application and soil management.