Forage crop nitrogen recovery and nitrogen field-losses determined on semi-virtual dairy farms under integrated nutrient and crop management scenarios

In the Lower Fraser Valley region of BC, intense dairy production occupies a relatively small agricultural land base. Farm-generated manure is often applied to forage crops at a very high rate to deal with the large quantities produced by high animal density. Local farmers also purchase additional mineral fertilizer to maximize production and profitability, which together with manure has far exceeded the nutrient uptake capability of crops. Surplus nitrogen (N) will lead to N loss through nitrate leaching and nitrous oxide emission. The objectives of this study are to quantify and compare (1) the crop N removal and apparent recovery of total N applied (TNR); and (2) nitrous oxide emission and nitrate leaching intensity of four dairy farm management scenarios that incrementally introduce beneficial management practices (BMPs) and advanced production techniques. I compared these four scenarios for annual crop yield, crop N removal, and TNR of silage corn and tall fescue. I quantified the seasonal and annual N field-losses through nitrous oxide emission and potential nitrate leaching. Finally, I also examined how adjusting cropland allocation would affect total crop yield, crop N removal, TNR, and N field-loss for the four scenarios. Planting a relay crop removed more N from corn plots while producing a similar amount of feed as the conventional scenario and also reduced nitrate leaching and leaching intensity by 70 %. Reduced grass harvest frequency increased grass yield substantially. Nitrification inhibitor, DCD, and irrigation improved TNR of both corn and grass and also reduced nitrous oxide emission from grass plots in 2017 and corn plots in 2018. In the dual-crop forage production system of 50 % corn and 50 % grass, TNR increased significantly only when all available BMPs of this study were integrated. Total nitrate leaching intensity abated more than 50 % when the relay crop and reduced grass harvest frequency were implemented. Adding DCD and irrigation reduced annual total nitrous oxide emission intensity by 40 %. Allocating 10 % more land to grow corn increased total feed production, but had little impact on total nitrate leaching and nitrous oxide emission.Land and Food Systems, Faculty ofGraduat