Nutrient management modulates acidification-induced risks to yield and cadmium contents in paddy rice

Cropland acidification in China has decreased crop yields and accelerated cadmium accumulation in edible crops. Enhancing manure recycling effectively mitigates soil acidification but increases the risks for cadmium accumulation due to elevated cadmium contents in manure. Here we coupled a dynamic cadmium model with the soil acidification model VSD+ to assess the spatial-temporal impacts of nutrient management on soil acidification and cadmium dynamics in a typical Chinese paddy rice system. Enhancing manure recycling decreased soil acidification and almost completely reduced mineral phosphorus fertilizer use, but accelerated soil cadmium accumulation through increased manure cadmium inputs and reduced cadmium leaching. Raising soil pH without lowering cadmium inputs reduced rice cadmium contents in the short to medium term, but continued soil cadmium accumulation offset these benefits in the long term. Under current cadmium deposition levels, only around 20% of the manure can be safely recycled without exceeding cadmium safety thresholds, which is lower than the current manure recycling ratio of 30%. When cadmium deposition is minimized, the manure recycling ratio can increase up to 85%. To enhance manure recycling sustainably, a lowering of cadmium content in manure and cadmium deposition is required.