Effects Of Rapeseed Cake On Cadmium Bioavability In Paddy Soil,and Cadmium Translocation In Rice Plants

It has been found that there are different results on the effects of organic manure applying on Cd bioavailability in paddy soil and on Cd uptake and accumulated by rice plants.Some scholars believe that application of organic manure can reduce Cd activity in soils,and increase soil fertility and increase crop yields.On the contrary,some studies have pointed out that application of organic compounds in paddy soils significantly increases rice yield,but has no significant effects on Cd accumulation in crops planting in Cd-polluted soils,and even significantly enhances Cd accumulation in crops.Rapeseed cake(RSC)is a common agricultural organic fertilizer in the rural areas of Hunan Province.In many areas,RSC is used as organic manure to paddy field and increases soil fertility so as to increase rice yield.At the same time,there is a large area of moderate and mild Cd-polluted rice fields in Hunan Province.How does application of RSC affect Cd bioavailability in such polluted paddy soils and affect Cd uptake and accumulation in rice? Does RSC inhibit Cd uptake by rice,reduce the risk of soil Cd pollution or not? Does RSC increase rice yield and ensure the safety of food production at the same time? How does RSC affect Cd translocation and accumulation in the soil-rice system? All of those problems are urgently studied.For those reasons,a series of experiments were conducted to study the effects of applying RSC on Cd bioavailability in paddy soils and on Cd translocation in rice plants.The results of paddy cultivation experiments showed that application of RSC significantly reduced Cd bioavailability in soils at the early stages of rice growth.However,this decreasing effect gradually weakens following rice growth extended.The effects of RSC on Cd availability in the soil might be divided into two processes: the Cd stabilization period(early stage of rice growth)and the Cd release period(later stage of rice growth).The effect of iron plaque on the rice root surface with RSC treated might be divided into two processes: the inhibition of Cd into rice root(early stage of rice growth)and no effect or promotion of Cd into rice root(later stage of rice growth).The application of RSC to increase rice yield,but it is not conducive to reduce the accumulation of Cd in rice,and even significantly increased the Cd content of rice brown rice.Through the study of soil physicochemical properties(soil pH and organic matter content),dissolved organic carbon,nitrogen,soil Cd fractions(BCR method),soil microbial biomass,soil enzyme activity,and iron plaque onto root surface,this thesis explained the reasons leading to the above results.Therefore,it should be cautious to amend the use of RSC in field experiments so as to improve soil fertility.