Objective The aim was to explore the effects of straw returning to combined with organic fertilizer application on morphological changes, migration and accumulation of cadmium in soil-rice plant system of acidic paddy fields, which could provide an application of straw-organic fertilizer synergy in immobilizing active cadmium (Cd) in soil and reduce Cd accumulation in rice.

Method A field plot experiment was conducted to investigate the changes in Cd bioavailability, migration, and accumulation within the rice-soil system across different growth stages under varying proportions of straw and organic fertilizer application (Straw: Organic Manure= 0:4; 3:1; 2:2; 1:3; 4:0, marked as S, SO1, SO2, SO3, O).

Result Straw returning combined with organic fertilizer application improved soil pH, with a 0.28 unit (P < 0.05) increase observed in rice soil under O treatment at the tillering stage. Soil available sulfur, Fe²⁺, and dissolved organic carbon (DOC) levels significantly increased with elevated organic fertilizer application rates, with respective increments of 50.7%, 30.8% and 26.8% observed under the O treatment (P < 0.05). At both the tillering and heading stages, soil available Cd contents significantly decreased with increasing proportions and application rates of organic fertilizer. Specifically, under the O and SO3 treatments, soil available Cd contents were reduced by 16% ~ 32% (P < 0.05). This reduction may be attributed to organic fertilizer-induced increases in soil organic matter and cation exchange capacity, which enhance Cd immobilization. The combined application of straw and organic fertilizer effectively reduced Cd accumulation in rice, with the lowest rice grain Cd content observed under the O treatment, showing a significant decrease of 32.9% (P<0.05) compared to the control. While sole straw incorporation was insufficient to maintain rice yield, increasing organic fertilizer application rates effectively enhanced yield. Notably, the O and SO3 treatments achieved comparable productivity than those of conventional chemical fertilizers, demonstrating their potential as sustainable alternatives.

Conclusion The obtained results have demonstrated that the combined application of straw incorporation and organic fertilizer significantly enhances the pH of acidic soils. Specifically, either 9000 kg hm⁻² of organic fertilizer alone or a combined application of 2250 kg hm⁻² organic fertilizer with 6750 kg hm⁻² straw can effectively substitute chemical fertilizers. These measures not only maintain rice yield, but also reduce Cd migration efficiency within the soil-rice system, thereby significantly decrease Cd accumulation in grains.