Cadmium Availability in a Soil-Rice System Receiving Four Consecutive Seasons of Straw Removal

Cadmium (Cd) pollution in rice agroecosystems has become a pressing worldwide environmental challenge. Straw return leads to Cd re-entering the soil, yet the impact of straw removal (SR) on Cd mobility and bioavailability within this system remains unclear. We implemented a four-season field study to evaluate how different SR intensities (NSR: no rice straw was removed; HSR: half of the rice straw was removed; TSR: all the rice straw was removed) influence Cd availability in this system. Our findings indicated that after three and four consecutive seasons of SR, the DTPA-extractable Cd levels showed notable reductions of 12.2% and 13.7%, respectively. SR also decreased grain Cd concentration (Cd_G) in subsequent seasons, demonstrating a dose-dependent response. The Cd_G after one, two, three, and four seasons of TSR treatment fell by 9.0%, 25.2%, 16.8%, and 41.7%, respectively, compared to that following NSR treatment. Notably, late-season SR proved more effective in Cd_G reduction than early-season SR. Statistical analysis confirmed a strong positive association between Cd_G and DTPA-extractable Cd. The primary mechanism underlying Cd_G reduction appears to be the decreased Cd bioavailability in soil resulting from SR practices. These findings establish multi-season total straw removal as a sustainable phyto-management strategy for Cd-polluted rice cultivation systems.