Greenhouse gas mitigation and soil carbon stabilization potential of forest biochar varied with biochar type and characteristics.

Biochar is increasingly used in climate-smart agriculture, yet its impact on greenhouse gas (GHG) emissions and soil carbon (C) sequestration remains poorly understood. This study examined biochar-mediated changes in soil properties and their contribution to C stabilization and GHG mitigation by evaluating four types of biochar. Soil carbon dioxide (CO2) and nitrous oxide (N2O) emissions, soil chemical and biological properties, and soil organic carbon (SOC) mineralization kinetics were monitored using greenhouse, laboratory, and modeling experiments. Three pine wood biochars pyrolyzed at 460 °C (PB-460), 500 °C (PB-500), 700 °C (PB-700), and one pine bark biochar from gasification at 760 °C (GB-760) were added into soil at 1 % w/w basis. Soils amended with biochar were used to cultivate sorghum for three months in a greenhouse, followed by three months of laboratory incubation. Data obtained from laboratory incubation was modeled using various statistical approaches. The PB-500 and PB-700 reduced cumulative N2O-N emissions by 68.5 % and 73.9 % and CO2 equivalent C emissions by 66.9 % and 72.4 %, respectively, compared to unamended control. The N2O emissions were positively associated with soil nitrate N, available P, and biochar ash content while negatively associated with SOC. The CO2 emission was negatively related to biochar C:N ratio and volatile matter content. Biochar amended soils had 49.2 % (PB-500) to 87.7 % (PB-700) greater SOC and 22.9 % (PB-700) to 48.1 % (GB-760) greater sorghum yield than the control. While PB-700 had more saprophytes than the control, the GB-760 yielded a greater yield than biochars prepared by pyrolysis. Microbial biomass C was 7.23 to 23.3 % greater in biochar amended soils than in control. The double exponential decay model best explained the dynamics of C mineralization, which was associated with initial soil nitrate N and available P positively and total fungi and protozoa biomass negatively. Biochar amendment could be a climate smart agricultural strategy. Pyrolysis pine wood biochar showed the greatest potential to reduce GHG emissions and enhance SOC storage and stability, and gasification biochar contributed more to SOC storage and increased crop yield.

Long-term Management Effects and Temperature Sensitivity of Soil Organic Carbon in Grassland and Agricultural Soils.

Soil organic carbon (SOC) is integral to soil health and agroecosystem resilience. Despite much research, understanding of temperature sensitivity of SOC under long-term agricultural management is very limited. The main objective of this study was to evaluate SOC and nitrogen (N) dynamics under grasslands and winter wheat (Triticum aestivum L)-based crop rotations in the inland Pacific Northwest (IPNW), USA, and measure SOC mineralization under ambient and elevated incubation temperatures. Soil samples were collected from 0-10 and 10-20 cm depths from an undisturbed grassland (GP), winter wheat-pea (Pisum sativum L) rotations under conventional tillage (WP-CT) and no-tillage (WP-NT), and winter wheat-fallow rotation under conventional tillage (WF-CT) and analyzed for SOC and N pools. Soil samples were incubated at 20 °C and 30 °C for 10 weeks, and SOC mineralization rates were estimated using the first order kinetic model. The GP had the greatest amounts of SOC, total N (TN), and microbial biomass carbon (MBC) and WP rotations had higher inorganic N content than other treatments. The SOC mineralization at elevated incubation temperature was 72-177% more than at the ambient temperature, and the greatest effect was observed in GP. The SOC storage under a given management did not have consistent effects on soil carbon (C) and N mineralization under elevated temperature. However, soil disturbance under WP-CT and WF-CT accelerated SOC mineralization leading to soil C loss. Reducing tillage, integrating legumes into crop rotations, and growing perennial grasses could minimize SOC loss and have the potential to improve soil health and agroecosystem resilience under projected climate warming.