Impact of tillage and straw management on cadmium bioavailability and uptake in rice: A long-term field study

Tillage practices alter the interaction between soil and rice straw, impacting soil quality and cadmium (Cd) dynamics. However, the effects of tillage and straw management strategies on soil Cd accumulation and rice uptake remain unclear. This study investigated how tillage and straw practices influence rice Cd uptake by altering soil Cd mobility and bioavailability. A long-term field experiment was conducted with four treatments: no-tillage with straw return on the soil surface (NTS), rotary tillage with straw incorporation (RTS), plow tillage with straw incorporation (PTS), and plow tillage with straw removed (PT). Results showed that Cd concentrations in rice organs (root, stem, leaf, and rice grain) decreased in the order NTS>RTS>PTS, with only PTS maintaining grain Cd levels below 0.2 mg kg^–1. Compared with NTS and RTS, the average Cd concentrations in rice grain under PTS were significantly reduced by 56.76 and 25.88%, respectively. A partial least squares path model indicated that reductions in available Cd (Avail-Cd) and acid-soluble Cd (Aci-Cd), combined with iron plaque (IP) formation on the roots, were key factors in lowering rice Cd levels. PTS reduced Avail-Cd and Aci-Cd by decreasing soil bulk density, increasing soil organic matter, pH, and the abundances of Nitrospirota and Bacteroidota. Moreover, PTS enhanced soil nutrient and Fe²⁺ levels, promoted IP formation on rice roots through improved root morphology and antioxidant activity, and limited Cd uptake. Although PTS increased total and available soil Cd compared to PT, its promotion of IP formation mitigated rice Cd uptake, resulting in comparable grain Cd concentrations between the two. Thus, long-term plow tillage with straw incorporation emerges as a sustainable practice to enhance soil quality and reduce Cd uptake in the rice cropping system.