Reduction in Greenhouse Gas Emissions from Dairy Cattle Manure Applied to Soil with Biochar.

Dairy cattle manure is an abundantly available soil amendment which needs on-farm management to proactively reduce unwanted gas emissions and nutrient-related ground and surface water quality concerns at both point and non-point sites. The addition of dairy cattle manure to soil provides organic and nutrient substrates that heighten carbon mineralization and alter nutrient cycling pathways in soil and GHG emissions. This field study evaluated an alternative approach for managing dairy cattle manure by integrating application with biochar. The objective of this field study was to evaluate the impact of biochars, dairy cattle manure, and manure + biochar on the GHG (CH₄, CO₂, and N₂O) emissions from soil. The three biochars used in this study were produced from carbon optimized gasification of corn stover (Zea mays L.), Ponderosa pine (Pinus ponderosa Lawson and C. Lawson) wood residue, and switchgrass (Panicum virgatum L.). There were five treatments with four replications which included corn stover biochar, Ponderosa pine wood biochar, switchgrass biochar, dairy cattle manure, dairy cattle manure + Ponderosa pine wood biochar. These amendments were applied at 10 Mg ha^-1 to Maddock soil (sandy, mixed, frigid Entic Hapludolls) located in an eroded upper landscape position and a Brookings soil (fine-silty, mixed, superactive, frigid Pachic Hapludolls) located in a depositional landscape position. The cropping system comprised of corn, soybean, and soybean during our field study (2013-2015). Greenhouse gas (GHG) fluxes were measured weekly. Soil C and N dynamics were determined by monitoring the changes in the concentration of their speciation twice a year (before and after the crop growing season). Cumulative methane (CH₄) emissions were not influenced by treatments with no particular pattern in flux data irrespective of year and soil type (landscape position). Manure treatment had the highest cumulative CO₂, and N₂O emissions. But there was mitigation of CO₂, and N₂O emissions observed in dairy cattle manure + Ponderosa pine wood biochar. All biochar treatments had lower N₂O emissions compared to control and manure treatments. This study indicated the possibility of reducing GHG emissions and enhancing the stabilization of manure fractions in soil by applying with biochar.