Tillage, cover crop, and biochar affect crop productivity and soil carbon on Andisols

Long‐term sustainability of organic crop cultivation depends on management systems that simultaneously maintain soil fertility and productivity. However, the plausible combined effects of tillage systems, cover crops, and biochar under varying organic rotation systems remain ambiguous, especially in soils containing volcanic ash with inherently high organic matter. Thus, a two‐cropping‐year field experiment (2022–2024) was conducted at a site with >20 years of no tillage (NT) research history in Kanto, Japan. It evaluated the interactive effects of tillage methods (moldboard plow [MP], rotary tillage [RT], and NT), winter cropping systems (wheat [ Triticum aestivum L.] monoculture at 50 or 100 kg ha −1 , or wheat–hairy vetch [ Vicia villosa Roth] mixture at 50 kg ha −1 each), and biochar application (0 or 8 t ha −1 ) within an organic soybean [ Glycine max (L.) Merr.]–wheat rotation system. The soybean yield under NT was comparable to or significantly higher than under RT, but wheat yield was greater under MP. No‐tillage significantly increased the soil organic carbon (SOC) levels of the 0–7.5 cm layer, lowered bulk density, and improved surface soil structure. Biochar further enhanced the SOC across all soil depths, but not short‐term yields. Cover crops increased SOC and wheat plant height, suggesting improved nutrient cycling, although the effects on yield were limited. These findings demonstrate that integrating NT and biochar supplementation can enhance SOC sequestration without compromising legume yield under organic conditions; however, cereals may require periodic tillage to maintain productivity. This study provides quantitative evidence for designing crop‐specific conservation systems and carbon (C) farming strategies for use with Andisols.