Soil pH and micronutrient thresholds decide whether legume rotations deliver climate benefits in China

A large field study across China's major farming zones found that soil chemistry, not just the legume crop, controls how well legume rotations improve soil health. Researchers analyzed 213 soil samples from legume systems and found soil pH was the strongest predictor of soil multifunctionality, with higher pH linked to lower performance. Micronutrients like zinc, iron, and manganese only helped within specific thresholds, and soil carbon and nitrogen ratios also set limits. These results matter for sustainable agriculture and carbon programs. Legume rotations are often promoted to cut synthetic fertilizer use and build soil carbon, but the benefits depend on local conditions. Alkaline, carbon-poor soils in China's warm-temperate zone underperformed, while colder plateau soils did better. The authors suggest testing pH, nutrient stocks, and micronutrient levels before assuming a legume rotation will reduce emissions or store carbon.