Reducing nitrous oxide emissions from irrigated maize by using urea fertilizer in combination with nitrapyrin under different tillage methods

The aim of this study was to evaluate the effectiveness of nitrification inhibitor (nitrapyrin; NI) as a mitigation option for yield-scaled emissions of nitrous oxide (N2O) under tillage management and urea fertilization in the irrigated maize fields in northern Iran. A split-plot experiment was performed based on a randomized completed blocks design with three replicates. The main plots were the levels of tillage practices (conventional tillage (CT) and minimum tillage (MT), and the subplots were the fertilizer treatments (control, urea, and urea + NI). The gas samples for measuring N2O emissions were collected during the maize growing season from June to September, using opaque manual circular static chambers. Soil samples were taken at 0-10 cm to determine water-filled pore space, ammonium (NH4+), and nitrate (NO3-) concentrations in the soil. When the crop reached physiological maturity, maize was harvested to measure grain yield, biomass production, N uptake of aboveground, and nitrogen use efficiency (NUE). The results showed that the applying NI in combination with urea reduced the total N2O emissions by up to 58% and 64% in MT and CT, respectively. In the urea + NI treatment, mean soil concentrations of NH4+ and NO3- were significantly higher (20%) and lower (23.5%), respectively, compared with other treatments. The NI reduced the yield-scaled N2O-N emission up to 79% and 55% for CT and MT, respectively. Furthermore, compared to treatment with urea alone, the application of NI increased the NUE of the MT and CT systems by an average of 55% and 46%, respectively. This study emphasized that the application of nitrapyrin should be encouraged in irrigated maize fields, in order to minimize N2O emissions and improve NUE and biomass production.