Sugarcane Straw, Soil Temperature, and Nitrification Inhibitor Impact N2O Emissions from N Fertilizer

Sugarcane straw is a source of carbon (C) and nitrogen (N), which affect soil temperature and moisture and therefore soil nitrous oxide (N2O) emissions from fertilized fields. The use of a nitrification inhibitor (NI) with N fertilizers is an option to reduce N2O production; however, sugarcane straw may interfere with the efficiency of a NI to reduce these losses. We conducted two laboratory studies over nearly 100 days to evaluate the following: (i) the implications of sugarcane straw removal and N fertilization under different temperatures on N2O emissions and (ii) the efficiency of a NI to reduce N2O emissions as determined by straw rates. In the first experiment, the treatments were as follows: N (0 and 100 kg ha−1), straw (0 and 8 Mg ha−1), and soil temperature (20 and 30 °C); in experiment 2, we included another straw rate (16 Mg ha−1) and NI dicyandiamide (DCD) (10 kg ha−1). Straw increased N2O emissions from N fertilizer by 37-fold and 3-fold in experiments 1 and 2, respectively. The N2O emissions were 62% higher at 20 °C than at 30 °C, whereas the opposite was observed for CO2 emissions. There was a synergistic effect of straw, which increased the dissolved organic C by more than 50% in the topsoil layer and was positively correlated with N2O emissions. The NI strongly reduced N2O emissions (> 63%) regardless of the straw rate, with no effect on soil respiration. The use of NI is an important strategy to mitigate N2O emissions from N fertilization in sugarcane fields where harvest residues are preserved.