Modeling growing season and annual cumulative nitrous oxide emissions and emission factors from organically fertilized soils planted with barley in Lethbridge, Alberta, Canada

Abstract

The widely used Denitrification-Decomposition (DNDC) model does not explicitly account for the influence of microbes in organic fertilizer. However, applying organic fertilizers to soils may increase N2O emissions because organic fertilizers can contain appreciable levels of the plant-available nitrogen (N), and contain many types of microbes including denitrifiers. In this study, the DNDC model was extended to include a microbial factor to account for the enhancement of microbial contents by the organic fertilizer input, and applied to two organically fertilized (digestate and manure) soils planted with barley in Lethbridge, Alberta, Canada. The growing season cumulative N2O emissions at the recommended N rate of digestate and manure were used to calibrate the model, while the emissions at the double recommended N loadings were used for validation. The results show that the growing season cumulative N2O emissions at recommended N loadings were calculated to be 1.90, 1.62, 3.50, and 2.55 kg-N ha−1 for digestate, and 0.45, 0.17, 0.35, and 0.74 kg-N ha−1 for manure in 2008, 2009, 2010, and 2011 respectively. The corresponding emission factors (EFs) are 0.937, 0.444, 1.947, and 0.510, as well as 0.095, 0.035, 0.072, and 0.083 for manure in 2008, 2009, 2010, and 2011 respectively. The average four-year relative errors of N2O emissions and EFs of validated cases are 32.3% and 34.3% for digestate, as well as 66.9% and 126% for manure, respectively. Two-factor hyperbolic and quadratic models of emissions and EFs correlating N loadings and weather conditions were developed and applied to N2O emission data at recommended N loadings. The coefficients of determination of modeled EFs to measured values are 0.887 and 0.982 for digestate and manure, respectively. The two-factor hyperbolic model predicted that N2O EFs would range from 0.085% to 1.1% for digestate with N loadings ranging from 100 to 800 kg-N ha−1, and product of average precipitation and air temperature during the growing season ranging from 18 to 36 mm × oC. The corresponding emissions ranged from 1.0 to 5.1 kg-N ha−1. We conclude that N2O emissions and EFS could be effectively modeled by a two-factor hyperbolic equation for digestate, and quadratic equation for manure.