Optimizing cadmium reduction in ratoon rice through micro-alkaline irrigation with nanomaterials: Implications for...

Cadmium (Cd) accumulations in both main and ratoon rice pose significant risks to food safety. Here, we evaluated micro-alkaline irrigation water containing calcium carbonate nanoparticles (NCC) and hydroxyapatite nanoparticles (NHAP) for Cd mitigation in main (MC) and ratoon crops (RC). Pot and field experiments assessed soil Cd availability, iron plaque formation, and Cd translocation under varying application strategies (soil basal and micro-alkaline irrigation) and retained stubble heights after main rice harvest (20 cm and 40 cm). The results showed that micro-alkaline irrigation (C + P 10:1) reduced soil DTPA-Cd by 39-53 % and enhanced iron plaque Cd sequestration by 63-108 %, thereby reducing Cd in brown rice by 59 % for MC and 63 % for RC. Elevated soil pH (11-24 %) and optimized Fe/Mn oxide adsorption suppressed Cd uptake and translocation. Higher stubble height (40 cm) further reduced RC grain Cd by 11-28 % via restricted root-to-shoot transport. Structural equation modeling highlighted soil pH, DCB-Fe/Mn, and DTPA-Cd as key drivers of Cd accumulation. This strategy offers a sustainable approach to minimize Cd in rice while improving yields, demonstrating potential for safe grain production in contaminated soils.