A Three-Year Field Study to Assess the Impact of Biochars and Dairy Manure on Soil Nitrous Oxide Emissions.

A three-year field study was conducted with an objective to evaluate the impact of biochars, dairy manure, and manure + biochar on soil nitrous oxide (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 manure, dairy 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 soybean, soybean, and corn during our field study (2014-2016). Soil N₂O 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). Crop grain yields were also determined to evaluate the agronomic performance of these treatments.