Soil greenhouse gas emissions, organic carbon and crop yield following pinewood biochar and biochar–manure applications at eroded and depositional landscape positions: A field trial in South Dakota, USA

Soil amendments can help reduce greenhouse gas (GHG) emissions and increase soil organic carbon (SOC) and crop yield. However, most biochar studies have been conducted on single soil type under controlled conditions. To address this limitation, the aim of this research was to investigate how field biochar and manure applications affect soil quality, plant productivity, and GHG emissions at eroded (sandy loam) and depositional (clay loam) positions in a climate transition zone (udic to ustic and mesic to frigid temperature). A field study was established in 2013 in South Dakota, USA, under a corn–soya bean rotation. Soil treatments included biochar, manure, a manure and biochar mixture, and a control (untreated soil). Soil properties (pH, electrical conductivity (EC), SOC, available nitrogen, available phosphorus and available potassium) were measured in 2017. Plant productivity parameters in 2016 and 2017 and GHG fluxes were measured during the 2016 and 2017 growing seasons. Compared with the control, SOC increased under all treatments at the eroded position (biochar 26%, manure 24%, and manure–biochar mixture 15%) and increased under biochar (25%) and the manure–biochar mixture (25%) at the depositional position. Plant parameters were similar under all treatments at both positions. Area‐scaled CO₂ fluxes were lower in soils treated with biochar compared with the control at the eroded landscape position but not at the depositional landscape position. Area‐scaled N₂O fluxes were lower in soils treated with biochar at both positions. Furthermore, the biochar–manure mixture treatment emitted lower area‐scaled N₂O fluxes compared with manure alone at both positions. This study suggests that for eroded and depositional landscape positions, biochar can improve soil organic carbon and the effects of the biochar and biochar–manure mixture on GHG emissions vary based on the soil texture.