Short-term responses of soil health and net biome production to no-till cover cropping: a case study of silty clay soil in a humid continental climate

Sustainable management practices are promoted to achieve dual outcomes of mitigating climate change and sustaining crop productivity. In particular, no-till with cover crops introduces greater plant-derived biomass C and enhances nutrient cycling for subsequent seasons. However, whether this practice improves soil health and further facilitates crop productivity and net biome production (NBP) in the short term remains unclear. Therefore, this study aimed to evaluate the effects of management practices on NBP and soil health, and the relationship between soil health and yield. A soybean field trial was conducted at the Field Science Center for Northern Biosphere, Hokkaido University, Japan, to examine the first two-year effects of rye [Secale cereale, cv. R-007] cover cropping under no-till without fertilizer (NT-WC), compared with CT-CF (tillage + chemical fertilizer), CT-NF (tillage + no chemical fertilizer), and NT-NF (no-till + no chemical fertilizer). Haney’s Soil Health Test (HSHT), which quantifies soil health score (SHS), was employed to evaluate seeding and harvest stages in 2024 and 2025 by measuring the parameters: CO₂ burst, water extractable organic carbon and nitrogen (WEOC, WEON) (calculated as WEN minus NO₃^--N and NH₄⁺-N). NBP was calculated from plant-derived biomass carbon and heterotrophic respiration (Rh), measured using the static closed-chamber technique. Three-way ANOVA, Pearson’s correlation analysis, and regression analysis were used to examine the differences among treatments over two years, the driver parameter of SHS, and the relationship between SHS and grain yield, respectively. The results showed that the only positive NBP value in the first year under NTWC, with higher rye net primary production (NPP), declined significantly in the second year from 1.56 to −4.70 Mg ha^-1 due to reduced soybean aboveground NPP and increased Rh. In addition, grain yields in the second year under NT were significantly lower than those under CT and also significantly decreased relative to the first year. Second-year yield was strongly associated with soil bulk density, particularly in the 0–5 cm layer (r=－0.82; P<0.0001). Tillage reduced bulk density in the CT treatment and thereby alleviated yield and biomass limitations. SHS ranges from 0 to 50, with higher values indicating higher microbial activity and nutrient cycling potential. SHS had no significant differences among treatments but varied over time (mean 16.4 → 7.0 → 8.4 → 29.4), driven by elevated CO₂ burst, WEON, and WEOC. These patterns coincided with significantly higher Rh in the second year (except for CT-NF), likely reflecting enhanced microbial activity and increased residue decomposition. SHS at seeding was significantly correlated with grain yield under NT treatments. Overall, the no-till with cover crops system decreased yield and NBP and did not result in a clear improvement in soil health. Reduced tillage and the inclusion of physical soil properties in managing soil health may guide to optimize management, prevent crop yield loss, and enhance biomass production in further trials in this pedoclimatic context.