Soil Nitrate Retention and Nitrous Oxide Emissions Increase When Organic Fertilization Practices Are Amended with Biochar.

The interations between biochar (pyrolyzed biomass) and organic fertilization practices on greenhouse gas (GHG) emissions and mineral N in perennial agroecoystem soils have not been credibly studied. Biochar was added to two organic fertilization treatments: a cover crop and a grape pomace manure compost in a conservation-tilled vineyard (Cabernet Sauvignon, Vitis vinifera) in Oakville, CA. Soil gas emissions (N2O-N and CO₂-C), mineral N content (NO₃-N, NH₃-N) and gravimetric water content results were compared to controls as well as to conventional methods immediately following and between precipitation events. Treatments were established in February 2013 and arranged in a split-plot randomized complete block design. Significantly higher soil NO₃-N peak concentrations as well as lower N₂O_(g) flux rates were observed in the cover crop and compost treatments that contained biochar compared to the controls, but not in the no-N input conventional treatment containing biochar. There were no significant differences in CO₂ flux, NH₃-N (measured as NH₄), or gravimetric water content between biochar amended and un-amended plots within fertilization treatments. Our data suggest that biochar retains nitrate through sorption which could be available to microbes, enhancing denitrification potential which could explain higher N₂O _(g) fluxes after soil wetting in biochar treatments.