Mitigate N2O emissions while maintaining sugarcane yield using enhanced efficiency fertilisers and reduced nitrogen rates

Abstract

Conventional fertiliser nitrogen (N) inputs to sugarcane farming promote gaseous losses of the greenhouse gas nitrous oxide (N2O). This study investigated the effects of a nitrification inhibitor coated urea (NICU) and a 50:50 blend (N wt%) of polymer coated urea and conventional urea (PCU + U), both at a sub-recommended rate (112 kg N ha−1), on N2O emissions and productivity in a sugarcane crop. Three rates of conventional urea (70%, 100% and 130% of the recommended rate at 160 kg N ha−1) were also assessed. Nitrous oxide emissions were measured over a 7.5-month sugarcane crop using automatic chambers. High N2O emissions (> 50 g N2O–N ha−1 d−1) occurred in the first 2 months after fertiliser application, and the variability in daily emissions was best described by a combination of pH, soil nitrate concentration, soil temperature, water filled pore space and soil ammonium concentration. The blended PCU + U resulted in 62% higher, but non-significant, net fertiliser-induced N2O emissions, while NICU significantly reduced net emissions by 81%, compared to conventional urea at the same rate (112 kg N ha−1). Net emissions from conventional urea increased linearly with increasing rate, with a mean emission factor of 2.6%. Thus, applying NICU at 70% of the recommended rate achieved the greatest N2O emission reduction compared to a PCU + U blend or conventional urea at the same N rate. There was no significant reduction in yield when the fertiliser N rate was reduced to 70%. Further field trials are required to ascertain whether the use of reduced N rates and/or enhanced efficiency fertilisers can mitigate N2O emissions while maintaining or increasing productivity in the long term.