Increasing N use efficiency while decreasing gaseous N losses in a non-tilled wheat (Triticum aestivum L.) crop using a double inhibitor

Resumen

No tillage management is being encouraged nowadays to prevent soil erosion and contribute to carbon (C) sequestration. However, N fertilizer should be managed properly to optimize N use efficiency and to avoid the side-effects of losses of gaseous nitrogen (N), particularly those of ammonia (NH3), which are expected to increase due to the presence of residues in the topsoil. In this context, a non-tilled (two years after conversion from tillage) field experiment was set up in central Spain, in which urea treated with a combination of urease (N-butyl thiophosphorictriamide, NBPT) and nitrification (2-(3,4-dimethyl-1H-pyrazol-1-yl) succinic acid isomeric mixture, DMPSA) inhibitors was compared with the use of urea without inhibitors. Fluxes of NH3 (using the integrated horizontal flux method with three replicates), nitrous oxide (N2O), methane (CH4) and soil respiration were measured throughout the wheat (Triticum aestivum L.) cropping cycle under rainfed conditions, together with ancillary soil measurements (e.g., soil moisture and mineral N), yield and crop uptake of N. Gaseous N losses from urea without inhibitors accounted for 10.35% and 0.66% (for NH3 and N2O, respectively) of total N applied. The use of the double inhibitor resulted in a significant mitigation of both losses (by 50.5% and 91.6% for NH3 and N2O, respectively). The double inhibitor increased N use efficiency expressed as crop recovery efficiency and partial nutrient balance, and decreased N surplus, in comparison with urea without inhibitors. In spite of a similar grain yield, the unfertilized control had the lowest aboveground N uptake rate, due to the higher concentrations of grain and straw N for the fertilized treatments. Under the conditions of our study, NH3 volatilization in a short-term no-till managed field can be minimized using a double (urease plus nitrification) inhibitor. This strategy had no negative side effects on N surplus, CH4 uptake or N2O mitigation and led to a significant improvement of N use efficiency.