QUANTIFYING THE EFFECT OF SPRINKLER IRRIGATION ON GREENHOUSE GAS EMISSIONS

A declining area of arable land has heightened pressure to increase food production for a growing world population. The potential to enhance food production by increasing the number of irrigated farms is high on the Canadian Prairies. However, expansion of irrigated farms will likely influence agricultural greenhouse gas (GHG) emissions. Quantification and comparison of energy partitioning of surface energy fluxes, crop microclimatic modification, soil environment variation, and GHG emissions from irrigated and non-irrigated fields in the Canadian Prairies are explored in this research. The observed field data were also used to check the suitability of a regional version of a process-based GHG simulation model, the Denitrification-Decomposition (CDN-DNDC) model. It was found that irrigation alters energy partitioning noticeably, which promoted crop microclimatic modification leading to reduced vapor pressure deficit and canopy temperature. However, despite a much smaller proportion of the net radiation in non-irrigated systems being consumed by evaporation, the dryland fields did not exhibit markedly warmer soil temperatures. Soil water was found as the critical factor in influencing soil GHG emissions, and availability of soil nutrient was the dominant factor in soil N2O emissions from irrigated systems. The performance of the CDN-DNDC model to predict soil moisture under irrigation conditions during growing season was good, which allowed the model to be used to simulate different irrigated conditions. The CDN-DNDC model simulated and measured N2O emissions from irrigated and non-irrigated fields were compared, indicating that this model is suitable to assess N2O emissions from different management systems under irrigated conditions in the Canadian Prairies. According to the CDN-DNDC model, a future increase in irrigated fields will increase N2O emission. However, when crop yield is taken into consideration, there is actually a lower mean annual nitrous oxide intensity in the irrigated field. The performance of the CDN-DNDC model was less accurate in predicting N2O emission and soil water after the spring thaw, and in predicting soil temperature with respect to irrigation. This research provides a first look at energy partitioning, crop microclimatic, and soil environment modification, as well as GHG dynamics from irrigated agricultural fields in the Canadian Prairies