Interaction Between Soil and Fertiliser Nitrogen Drives Plant Nitrogen Uptake and Nitrous Oxide (N2O) Emissions in Tropical Sugarcane Systems

Aims High nitrogen (N) fertiliser inputs in intensive sugarcane systems drive productivity but also significant emissions of nitrous oxide (N 2 O), a potent greenhouse gas. Fertiliser and soil N availability for both plant N uptake and N 2 O 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 N 2 O emissions in two intensively managed tropical sugarcane systems. Methods High temporal resolution N 2 O measurements were combined with 15 N recoveries across four N fertiliser rates, (100, 150, 200 and 250 kg N ha − 1 ) in soil, plant and N 2 O emissions. Results Cumulative N 2 O emissions ranged from 0.3 to 4.1 kg N ha − 1 , corresponding to emission factors ranging from 0.7 to 2.4%. Native soil N accounted for > 60% of cumulative N 2 O emissions and total plant N uptake. Fertiliser N addition increased N 2 O 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 N 2 O emissions to N rates dependent on the site conditions. Overall fertiliser 15 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 N 2 O 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.