Nitrogen Fertilizer Formulations Modulate the Yield-Cadmium Trade-Off in Rice Through Rhizosphere Processes and Translocation Nodes.

Cadmium (Cd) contamination in paddy soils represents a major risk to global food security and human health because Cd can readily enter the food chain through rice consumption. Therefore, clarification of the key processes and mechanisms by which agronomic practices regulate Cd accumulation in rice is essential. Based on integrated two-year pot and field experiments, we showed that different nitrogen fertilizer formulations, including nitrate-N (N), ammonium-N (A), and urea (U), had distinct effects on Cd accumulation and grain yield in rice. The N treatment reduced Cd concentrations in brown rice by 25.29% to 70% in the pot experiment and by 4.25% to 89.97% in the field experiment but decreased grain yield by 5% to 25%. By contrast, the A treatment increased Cd concentrations in brown rice by 17.86% to 58.62%, while maintaining or slightly increasing grain yield (-3% to +5%), and the U treatment showed intermediate responses. These responses were mainly associated with nitrogen-induced shifts in rhizosphere chemistry, especially changes in soil Cd availability linked to pH and exchangeable H