Concomitant tracking of NH3, N2O and soil mineral-N using steady-state incubation cells to enhance sustainability of urea fertilization approaches

Abstract

Enhancing nitrogen use efficiency to assure sustainable intensification of crop production, while minimizing N-environmental threats, is a major challenge. These drive important developments of N-fertilization approaches and enhanced efficiency N-fertilizers (EENFs). The complexity of N-dynamics under different soils, environmental conditions, and application modes requires improvement of decision-making tools. Meta-analyses demonstrate the contribution of EENFs to sustainable intensification. Yet, improvements based on local field specific information, and particularly with new N-fertilization approaches, are needed. This project focuses on an upgraded laboratory designed steady state incubation system connected to a Long-Path gas cell mounted on an FTIR spectrometer, allowing fast determination of NH3 and N2O emissions concomitant with mineral N-dynamics in soils under different N-fertilization approaches. The system was tested with four representative soils, fertilized with surface applied urea or urea amended with urease inhibitors (UI). Different soil water saturation (WS) levels and urea application rates were tested over 14 days of incubation·NH3 losses (%N-applied) in the steady state system were 2 to 7 times higher than in the previously designed non-steady state system. Highest losses were observed when urea was applied to lighter soils with pH above 7.5 (~13% to 46%), especially under low (30%) water saturation (WS). Substituting to UI reduced the accumulated NH3 losses (14 days) by 55 to 92%. Highest N2O losses were obtained with the lighter soils (1.2% to 1.7%) at 50% WS and lowest urea application rate. UI assisted in reducing N2O losses in some of the tested soils, showing different dependencies on WS and urea concentration. This variety demonstrates the complexity of the N-processes involved under different soils and conditions, and was also expressed in the mineral-N concentrations. This simple experimental design has the potential to improve our insights and help evaluate EENFs sustainability.