Field and Farm Scale Nitrogen Budgeting Trade Offs Associated with Different Manure Application Strategies.

Understanding the fate of nutrients in land-applied manure is key to improving the efficiency of their use in crop production. We developed nitrogen (N) budgets for two years of continuously cropped corn fertilized by dairy manure via broadcast application or shallow disk injection. Major pathways and pools of N loss were monitored on 12, 0.04 ha field lysimeters in central Pennsylvania to estimate the impact of manure application method on N fate: gas emissions; off-site runoff (overland and subsurface flow); crop uptake; and soil storage. The budgets illuminated trade-offs in N cycling with each management strategy. Crop removal accounted for the largest portions of manure N applied in both budgets (16-43%). Broadcast manure N balances were more difficult to close and included a large proportion of ‘unaccounted’ N (36% and 58% of applied N for two accounting periods). Even so, results point to cumulative differences in nutrient use efficiencies that can be attributed to the greater conservation of ammonia-N with manure injection. The Integrated Farm System Model (IFSM) was used to simulate different manure management scenarios on a typical Pennsylvania dairy farm (100 milking cows, 80 ha), and compared with data from field experiments measuring ammonia volatilization, crop uptake and nitrate leaching. As predicted using IFSM, converting the operation from daily haul to 6 months of storage with broadcast application did not substantially change N losses to the environment. However, replacing broadcast manure application with shallow disk injection resulted in substantial conservation of ammonium-N and greater manure N use efficiency by crops, but slightly exacerbated nitrate-N leaching losses.