Effect Of Straw Returning On Soil Cd Activity And Cd Accumulation In Rice Plant

Direct returning of crop straws to agricultural fields is the most rational way to utilize straw resource and eliminate open-field burning of crop straws. However, large amount of active organic substances including dissolved organic carbon (DOC) is produced during the process of straw decomposition, which may affect heavy metal behavior in polluted soil, hi this study, pot experiments were carried out to investigate the rice growth and Cd accumulation in the Cd-polluted soil with wheat straw retuning, and to analyze the relationship between Cd solubility and the DOC level in the soil. The activation mechanism of straw retuning to Cd in polluted soil was discussed in this paper. Results obtained showed as following:(1) After the straw returning, both of the concentrations of DOC and Cd in soil leachate increased during initial period and then decreased. Straw returning elevated Cd and DOC level in soil leachate and a positive relationship between Cd and DOC concentration in soil leachate was observed in this study.(2) The straw returning inhibited the rice growth, and with the increase of wheat straw, rice biomass trended tol decline. This was probably due to the generation of reduced substances (e.g. organic acids) accumulation during the decomposition of the returned straw, which may detrimentally affect rice growth.(3) Cd contamination soils reduced biomass accumulation of rice, but the biomass was higher in Cd-contaminated soil than that in non-polluted soil, which indicated that Cd could consume the organic acids and relieve their harmful effect on rice growth.(4) In Cd contaminated soil, straw returning could elevate Cd content in rice root system, and the Cd concentrations in rice plant followed the order of:root> stalk> leaf. Straw returning enhanced Cd solubility in contaminated soil and Cd uptake by rice plant. However straw returning had detrimental effect on rice growth in this experiment, and average concentration of Cd in rice plant declined under straw retuning. (5) Under rice planting conditions, wheat straw retuning reduced both total and effective Cd content in rice soil, which meant that Cd activity and loss by leaching was enhanced by straw returning.