Interaction between soil and fertiliser nitrogen drives plant nitrogen uptake and nitrous oxide (NO) emissions in tropical sugarcane systems

Aims: High nitrogen (N) fertiliser inputs in intensive sugarcane systems drive productivity but also significant emissions of nitrous oxide (NO), a potent greenhouse gas. Fertiliser and soil N availability for both plant N uptake and NO emissions across different N rates remain unknown, hindering efficient N management. This study investigated the contribution of fertiliser and soil N and their interaction to plant N uptake and NO emissions in two intensively managed tropical sugarcane systems. Methods: High temporal resolution NO measurements were combined with N recoveries across four N fertiliser rates, (100, 150, 200 and 250 kg N ha) in soil, plant and NO emissions. Results: Cumulative NO emissions ranged from 0.3 to 4.1 kg N ha, corresponding to emission factors ranging from 0.7 to 2.4%. Native soil N accounted for > 60% of cumulative NO emissions and total plant N uptake. Fertiliser N addition increased NO emissions from native soil N compared to the unfertilised control, highlighting the interaction between fertiliser and soil N, which determined the overall magnitude but also the response of total NO emissions to N rates dependent on the site conditions. Overall fertiliser N loss responded exponentially to N rates with 50% of applied N fertiliser permanently lost even at the recommended N rate. Conclusions: The interaction between fertiliser and soil N and its contribution to N uptake and NO emissions demonstrate the importance of integrating soil fertility management with N fertiliser rate recommendations for sugarcane systems to maintain crop productivity and reduce environmental impacts.