Interaction between soil and fertiliser nitrogen drives plant nitrogen uptake and nitrous oxide (N$_2$O) 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. ... mehrOverall 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.