| Cadmium(Cd)is listed as one of the most dangerous environmental pollutants,and cadmium pollution has become one of the most concerned environmental issues.Nitrogen(N),phosphorus(P),and potassium(K)fertilizers are the basic fertilizers in agricultural production and play an important role in rice production.Reasonable application can affect soil p H,nutrients,and other physical and chemical properties,leading to changes in soil cadmium forms,thereby affecting the bioavailability of cadmium and plant uptake of cadmium.They have played an important practical role in regulating the absorption and accumulation of Cd in rice.This article sets up five treatments with different forms of N fertilizer(urea,ammonium bicarbonate),P fertilizer(calcium magnesium phosphate,superphosphate),and K fertilizer(potassium chloride,potassium sulfate)in combination.The aim is to study the effects of different forms of NPK fertilizer combination on the formation of iron film on the root surface of rice and the migration and transformation of Cd in the soil rice system,providing a theoretical basis and technical reference for the safe production of rice.The main research results obtained in this study are as follows:(1)The tiller number,leaf area index(LAI),and chlorophyll(SPAD)of the three growth stages of rice,namely tillering,heading,and maturity,showed an overall trend of increasing and then decreasing with the progress of the rice growth stage.The plant height,aboveground biomass,and underground biomass gradually increased with the growth of the rice,and the overall value of F05 treatment was the highest.The F05treatment increased the ear length,grain number,effective ear number,and yield by1.97%,8.70%,10.81%,and 3.93%compared to conventional fertilization,respectively.The yield of each treatment ranges from 10596.6 to 13613.1kg/hm~2,with an average yield of 12496.3 kg/hm~2.(2)The iron film on the root surface forms in large quantities during the tillering stage,and the content gradually decreases with the extension of the rice growth period.The content of iron oxide(DCB-Fe),manganese oxide(DCB-Mn),and iron film adsorbed Cd(DCB-Cd)in the mature stage decreased by 9.60%to 106.75%,11.36%to 46.00%,and 28.52%to 82.63%,respectively,compared to the tillering stage.The content of DCB-Fe,DCB-Mn,and DCB-Cd showed a highly significant positive correlation(P<0.01),and a highly significant negative correlation with the cumulative Cd content in rice roots.(3)Compared to conventional fertilization,each treatment increased soil alkaline nitrogen and available phosphorus by 5.29%to 11.87%and 7.94%to 8.19%,while reducing soil available potassium by 2.03%to 38.40%;The soil p H in the mature stage is 4.65-6.97%higher than that in the tillering stage,and the effective state is47.37%-104.35%lower than that in the tillering stage.F05 treatment has the best effect.The proportion of oxidizable Cd in soil is extremely low(6.08%～6.52%),and the majority of Cd exists in reducible and weakly acid extractable forms(59.39%～83.27%).Soil p H showed a highly significant negative correlation with available Cd(r=-0.70**),a significant positive correlation with weak acid extractable state(r=0.60*),and a highly significant and significant negative correlation with residual state,weak acid extractable state,and reducible state(r=-0.86**and r=-0.62*).Different application treatments mainly increase soil p H,reduce the extractable and reducible contents of weak acid in soil Cd,increase residual Cd,and thereby reduce the overall activity of Cd.(4)The accumulation of Cd in various parts of rice is as follows:root>stem>leaf>grain,and the maturity stage>heading stage>tillering stage.Compared with conventional fertilization,F05 treatment reduced the Cd content in rice roots,stems,leaves,and grains to varying degrees,with reductions of 35.05%,180.00%,205%,and 45.45%,respectively;F02～F04 treatment increased the Cd content in various parts of rice to varying degrees,increasing by 55.11%～228.01%,36.45%～273.75%,15.98%～89.25%,and 17.19%～120.31%,respectively.Cd in roots,leaves,and grains showed a highly significant negative correlation with p H(P<0.01),and a highly significant positive correlation with available state(P>0.01).In this study,F05 treatment is more conducive to promoting the growth and development of rice,increasing yield,forming iron film on the root surface,and reducing Cd content in various parts.It can be recommended as the best optimized fertilization model for this medium to low Cd polluted paddy soil. |
PDF Full Text Request