Response characteristics of soil Cd availability to microbes in paddy soil with long-term fertilization and its impact on Cd uptake in rice.

Long-term fertilization contributes to the accumulation of cadmium (Cd) in soils and crops, yet the effects of different fertilization regimes on soil Cd dynamics and its uptake in rice remain poorly understood. This long-term field experiment aimed to elucidate how different fertilization regimes influence Cd bioavailability and mobility in soil, thereby affecting Cd accumulation in rice. Four fertilization treatments were tested, including chemical fertilizer (CF), rice straw incorporation (RF), and low (LM) and high (HM) rates of manure fertilizers. Results revealed that manure fertilizers treatments (LM and HM) significantly reduced Cd concentrations in brown rice compared to other fertilization regimes, with levels falling below 0.2 mg kg. Compared to CF, the average Cd concentrations in brown rice under LM and HM were significantly reduced by 33.14 % and 15.88 %, respectively, and which was significantly reduced by 42.53 % and 27.70 % compared with RF. Additionally, the concentration of Cd in brown rice was significantly higher under HM than LM treatment. Partial least squares path model revealed that reductions in Avail-Cd and AciCd, coupled with the formation of low-crystalline iron plaque (IP-Feh and IP-Feh-Cd), were critical factors in decreasing Cd concentration in brown rice. Manure fertilizers reduced the availability of Cd in soil by increasing soil organic matter (SOM), pH, and the abundance of microbial phyla such as Latescibacterota and Gemmatimonadota. Manure application also increased cation exchange capacity (CEC) and Fe concentrations in soil, promoting IP formation on rice roots and effectively preventing Cd uptake. In conclusion, the application of manure fertilizers at low rates, particularly in combination with chemical fertilizer, is recommended to ensure the safe production of rice by mitigating Cd uptake.