Surface broadcast of dairy slurry is a common practice; however, concerns over nuisance odors and nutrient losses have prompted research into alternatives. Manure injection is one practice that addresses these concerns but is not widely adopted. Therefore, two studies were conducted to quantify NH3-N loss by volatilization, impacts on soil N cycling, and microbial response between surface broadcast and subsurface injection of dairy slurry. A constant air flow volatilization chamber system measured NH3-N losses and soil inorganic N, mineralizable carbon, and active microbial biomass. A 40-day static air incubation was performed to study nitrogen transformations over a longer period after application. Statistical significance was evaluated at the α = 0.05 level. In the volatilization study, subsurface injection reduced NH3-N losses by 98% and 87% in a clay loam and sandy loam, respectively, resulting in greater soil inorganic nitrogen compared with surface application. There were no significant differences in active microbial biomass between treatments. Surface application prompted greater microbial respiration in the sandy loam, but there were no significant differences between treatments in the clay loam. In the static incubation study, differences in soil NO3 −-N became significant on day 28, and by day 40, injection showed increases in soil NO3 −-N of 13% and 26% in the sandy loam and clay loam, respectively, relative to surface application. While the effect of subsurface injection on soil microbial response was unclear, it remains a tool that can greatly reduce NH3-N losses by volatilization and increase soil plant available nitrogen.
1Department of Crop and Soil Environmental Sciences, Virginia Tech, Blacksburg, Virginia.
2Department of Biological Sciences, Virginia Tech, Blacksburg, Virginia.
Current affiliation for Michael S. Strickland: Department of Soil and Water Systems, University of Idaho, Moscow, ID 83844.
Address for correspondence: Andrew M. Bierer, BS, 424 Smyth Hall, 185 Ag Quad Lane, Blacksburg, VA 24061. E-mail: firstname.lastname@example.org
Received March 31, 2017.
Accepted for publication July 12, 2017.