Soil health improvement and climate change mitigation in soybean agroecosystems

Although soil health indicator is extensively examined worldwide, Japan has yet to establish a soil health assessment framework calibrated to the unique properties of Andosols. In this study, we evaluated a long-term (19-year) organically managed soybean field and generated soil health scores using a cumulative normal distribution function to develop a site-specific benchmark. Treatments were tillage (no-tillage, moldboard plowing, and rotary tillage), cover crop (rye, hairy vetch, and fallow), and the addition of fertilizer or biochar in four replications. Intensive tillage reduced soil health, with soil health score under moldboard plowing significantly lower than no-tillage during 2020–2022 (p < 0.05). No-tillage with cover crop and biochar enhanced soil health status by sustaining soil organic carbon (SOC) at 3.8–4.8%. Overall soil health score was positively correlated with SOC (r = 0.7; p < 0.01), while higher soil health score was strongly associated with reductions in net global warming potential (rs = − 0.95; p < 0.01). SOC emerged as one of the most influential indicators, directly influenced soil ß-glucosidase activity (r = 0.84, p < 0.001), substrate-induced respiration (r = 0.7, p < 0.001), NO3– (r = 0.65, p < 0.05), and EC (r = 0.36, p < 0.01). Although NT-based systems may not achieve the highest yields due to interannual variability, they may offer substantial environmental benefits by contributing to long-term climate change mitigation.