Predicting nitrous oxide emissions after the application of solid manure to grassland in the United Kingdom

Nitrous oxide (N₂ O) emission from agricultural soils represents a significant source of greenhouse gas to the atmosphere. We evaluated the suitability of a modified Soil and Water Assessment Tool (SWAT) model to estimate the N₂ O flux from the application of solid manure at two grassland sites (North Wyke [NW] and Pwllpeiran [PW]) in the United Kingdom. The simulated N₂ O emissions were validated against field observations measured in 2011 and 2012 for model calibration and validation, respectively. The SWAT model predicts water-filled pore space (WFPS) very well with Nash-Sutcliffe efficiency (NSE), R² , RMSE, and percentage bias (PBIAS) values of 0.67, .72, 0.06, and 3.64, respectively, during the calibration period for NW site, whereas it gives 0.68, .69, 0.07, and 3.04, respectively during the validation period. At PW, the model predicted the NSE, R² , RMSE, and PBIAS of 0.55, .69, 0.04, and -4.5, respectively, during calibration and 0.63, .71, 0.05, and -2.6, respectively, during the validation period. Compared with WFPS, the model resulted in a slightly lower fit for N₂ O emissions for NW (NSE = 0.47, R²  = .63 during calibration, and NSE = 0.55, R²  = .58 during validation) and for PW (NSE = 0.54, R²  = .71 for calibration, and NSE = 0.47, R²  = .69 for validation). Results revealed that the SWAT model performed reasonably well in representing the dynamics of N₂ O emissions after solid manure application to grassland.