Subsurface Manure Applications for Conservation Tillage and Pasture Soils and Their Impact On the Nitrogen Balance.

Incorporating manures into soil with conventional tillage is an effective means to reduce ammonia volatilization and conserve manure nitrogen, however it is not possible in pasture and is not readily compatible with high-residue soil conservation practices for rowcrops.  A variety of manure injectors are available for liquid manures that provide subsurface application with limited disruption of the soil surface and residue cover.  These injectors can substantially reduce ammonia losses, with emissions generally proportional to the quantity of manure that remains on the soil surface.  However, greater losses of nitrogen through denitrification, and possibly leaching, could occur with subsurface manure application.  Placement of manures in concentrated below-ground bands increases the possibility of denitrification due to the higher rates of microbial activity in the bands that can deplete oxygen and create anaerobic conditions. Greater nitrate leaching could occur if the higher nitrate concentrations near the band intercept preferential flow pathways. This paper will summarize existing data evaluating the trade-offs associated with subsurface manure application, which is complicated by several factors: 1) limited data on nitrate leaching and denitrification following subsurface application; 2) the highly site-specific nature of preferential-flow leaching; 3) predicting the influence of weather conditions; and 4) the lack of a consensus on the costs associated with the emission of greenhouse gases (nitrous oxide and carbon dioxide) produced during denitrification, mineralization, and respiration.