Legumes or Nitrification Inhibitors to Reduce N2o Emissions in Subtropical Cereal Cropping Systems?.

The DAYCENT biogeochemical model was used to investigate how the use of fertilisers coated with nitrification inhibitors and the introduction of legumes in the crop rotation can affect subtropical cereal production and N₂O emissions. The model was validated using comprehensive multi-seasonal, high-frequency dataset from two field investigations conducted on an Oxisol, which is the most common soil type in subtropical regions. Different N fertiliser rates were tested for each N management strategy and simulated under varying weather conditions. DAYCENT was able to reliably predict soil N dynamics, seasonal N₂O emissions and crop production, although some discrepancies were observed in the treatments with low or no added N inputs and in the simulation of daily N₂O fluxes. Simulations were consistent with field observations and highlighted that the high clay content and the relatively low C levels of the Oxisol analysed in this study limit the chances for significant amounts of N to be lost via deep leaching or denitrification. The application of urea coated with a nitrification inhibitor (DMPP) was the most effective strategy in minimising N₂O emissions. This strategy however did not increase yields since the application of urea coated with a nitrification inhibitor did not substantially decrease overall N losses compared to conventional urea. Simulations indicated that replacing part of crop N requirements with N mineralised by legume residues is the most effective strategy to reduce N₂O emissions and support cereal productivity. The results of this study show that legumes have significant potential to enhance the sustainable and profitable intensification of subtropical cereal cropping systems on Oxisols.