Biochar and Organic Amendments Effects on Vineyard Scale Soil Greenhouse Gas Emissions and Nitrous Oxide Producing Pathways

Chapter 1: Biochar, compost, and cover crops in vineyard soils have the potential to sequester carbon in perennial agroecosystems, however, there have been conflicting studies on the effects these treatments have on nitrous oxide emissions and soil nitrogen status. Our study took place in a research vineyard in Napa Valley: we monitored N2O, CO 2, and CH4 emissions, as well as inorganic N pools of conventionally tilled "controls" and controls amended with compost or cover crops, each with or without biochar. We also calculated an estimated total belowground carbon allocation (TBCA) to determine the efficacy of each treatment at sequestering carbon. We observed no difference in greenhouse gas emissions between any of the treatments on a yearly scale; however, we did observe significantly more N2O flux for conventional plus biochar soils on an event scale. Compost plus biochar amended soils did significantly increase NO3 - pools compared to compost only and conventional treatments. Compost plus biochar treatments also had the highest TBCA of any other treatment. We suggest that compost plus biochar amendments could provide greater net carbon sequestration and increased inorganic N pools in vineyard soils compared to other organic fertilization practices while having little effect on greenhouse gas emissions.;Chapter 2: Biochar and compost amendments to soil are proposed strategies to increase soil carbon storage and improve inorganic N status in agricultural soils of orchards and vineyards. This study was conducted to increase understanding of biochar, compost, and biochar plus compost interactions on nitrification and denitrification activities, and to help develop a mechanistic basis for differences observed in inorganic N pools in a Mediterranean climate production vineyard. A secondary goal was to use this information to make inferences about long term N retention potential of biochar and compost soil treatments. Using a microcosm incubation, we employed the acetylene gas (C2H 2) inhibition technique by exposing conventionally managed soils (controls), biochar amended soil (1.2% w/w soil, to 10cm depth), compost amended soil (1.6% w/w soil, to 10cm depth), and biochar plus compost soil (1.2 % biochar + 1.6% compost w/w soil, to 10cm depth) to 0 or 0.1% C2H2 by volume headspace. Cumulative N2O and CO2 emissions, extractable inorganic N (NH4+ and NO3 -) and pH were measured. Biochar addition reduced nitrification in controls, but enhanced it when amended to compost treated soils. It was noted that denitrification was the primary N2O producing pathway for both biochar only and compost only treatments. Increased nitrification seen in compost plus biochar soils could be causal for observed higher NO 3- pools compared to compost alone treatment in the field.