Effects of nitrification inhibitor on rice yields and Cd uptake after milk vetch and rice straw returning in purple alluvial paddy soils in Hunan
The effects of rice straw return and nitrification inhibitors on rice growth and cadmium(Cd)uptake under the milk vetch-rice system were studied to provide theoretical support for safe rice production measures based on green manure in Hunan double-season rice fields.The micro-plot experiment included 4 treatments,i.e.,milk vetch only(GM),milk vetch with chemical fertilizer(GF),co-utilization of milk vetch and rice straw with chemical fertilizer(GRF),and co-utilization of milk vetch,rice straw and nitrification inhibitor(DMPP)and with chemical fertilizer(GRFD).The effects of different treatments on rice yield,nutrient accumulation,rice Cd uptake,soil fertility,soil Cd availability and Cd form were analyzed.Compared with GRF treatment,GRFD increased early rice yield by 7.0%and 12.2%,respectively.The nutrient accumulation of nitrogen,phosphor and potassium in grains of early rice in GRFD were significantly increased by 5.5%,10.1%and 6.8%,respectively,compared with GRF treatment.The Cd content in the early rice of the GF,GRF and GRFD treatments were decreased by 64.8%,67.3%and 66.8%,respectively,compared with the GM treatment.The contents of dissolved organic carbon and dissolved organic nitrogen in early rice of GRFD treatment decreased by 41.2%and 8.0%,respectively,compared with GRF treatment.Compared with GRF treatment,GRFD treatment significantly reduced the available Cd content in early rice and late rice soil by 70.9%and 66.0%,respectively.Compared with GF treatment,the soil available Cd of early and late rice in GRFD treatment were significantly decreased by 80.2%and 61.4%,respectively.Compared with GF treatment,the content of oxidizable fraction of Cd(Org-Cd)in late rice was increased by 52.6%in GRFD,indicating that co-utilization of milk vetch,rice straw and nitrification inhibitor could reduce soil Cd availability by transforming it into a form that is difficult to be absorbed by rice.Random forests and correlations showed that the soil available potassium and available phosphorus played a key role in limiting Cd uptake in both early and late rice.Under the condition of co-utilizing milk vetch and rice straw,combined application of nitrification inhibitors could increase rice yield,promote rice nutrient absorption,and reduce the absorption of Cd by increasing soil available potassium and available phosphorus contents.
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