| Based on National Monitoring Station of Soil Fertility and Fertilizer Efficiency on Purple Soils, this study was addressed effects of 24-year-long-term fertilization on Cd, Pb, Cr accumulation rule in wheat-rice system by saved soil and plant sample in different treatments and estimated the maximum bearing years of soil heavy metal with present fertilization and management. Using 4 model simulations,we analysised the adsorption-desorption characteristics of Cd on purple soil to reveal the impact of purple soil adsorption-desorption capacity in different treatments. The objectives of these studies were for rational application different fertilizer to estimate environment and agriculture products quality.Results showed that surface soil Cd, Pb, Cr with every treatment were accumulated obviously. After 24 years no-fertilization, CK treatment increased Cd, Pb, Cr contents in surface soil by 47.34%,5.59%,4.31%.In the situation, Cd increased significantly but Pb,Cr didn’t, which means other factors like atmospheric sedmentation would also cause soil heavy metal accumulating. Application of chemical P and oganic fertilizers and its great accumulation comtribution significantly affected Cd, Pb, Cr contents. Compared with CK, NK treatment didn’t increase significantly total Cd, Pb, Cr in soil, and NPK treatment increased Cd, Pb, Cr 162%,15%,77% contents, NPKM treatment increased Cd, Pb, Cr 393%,37%,312% contents. Compared with NPK treatment, NPKM treatment increased Cd, Pb, Cr 88%,20%,32% contents. Before the experiment, the Cd background value in purple soil was high relatively, so Cd content was beyond the National Level Two Soil Environment Quality Standard because of fertilization, atmospheric sedmentation and other reasons. The contents of Pb, Cr were safe in purple soil, and their bearing time were long, but fertilizer application would cut them down.Long-term-fertilization with different treatment have already affected heavy metal contents of grain and straw in rice and wheat. Compared with CK treatment, Cl-fertilizer and oganic fertilizer significantly increased Cd contents of rice grain 372%, 460%. Cd contents of Wheat grain with 1.5 times fertilizer and Cl-fertilizer application were 0.1114 mg/kg and 0.1594 mg/kg, which exceeded the National Level Two Soil Environment Quality Standard. Pb contents of grain in rice and wheat have no significant difference in every treatment. Fertilization had no effect on the accumulation of Pb in grain of rice and wheat, but the effect of Fertilization on straw was significantly increased. The content of Cr in rice grains was significantly higher than that in other treatments, but P treatment and CK treatment did not significantly different. The Cr content in all treatments was more than that of the national standard, and the effect of Fertilization on the accumulation of Cr in wheat grains was not affected. There was a large difference in the ability of heavy metals accumulation in rice and wheat. The accumulation ability of wheat to Cd was about 3-5 times stronger than that of rice and the accumulation ability of Cr in rice grain is about 5-8 times of that of wheat. The distribution of heavy metals in rice straw and grain, in general, was that Cd and Pb in the allocation of the straw were higher than that of the grain, Cr was higher than the straw. However, NPKM treatment increased the Cd translocation to rice grain, and the enrichment ability of Cd was higher than that of straw. In wheat, the accumulation of heavy metals in all treatments was greater than that in grain. From the production point of view, the situation was conducive to protect people’s food security.With the number of the years, the analysis experiment in soil heavy metal form and availability showed that fertilization increased the available Cd content of the soil. Long-term use of Cl-fertilizers significantly increased soil DTPA-Cd content, compared with CK treatment increased by 470%. P fertilizer and organic fertilizer application increased the soil available Cd, but the increase range of soil available Cd was significantly lower than that of the Cl-fertilizer. Single NK treatment significantly increased the content of DTPA-Pb in soil, with P fertilizer application, the content of DTPA-Pb was decreased. Which means the effectiveness of P fertilizer inhibited Pb. The results of heavy metal test by Tessier correction method showed, the content of exchangeable Cd in soil was significantly increased with Cl-fertilizer, and NPKM treatment significantly improved soil Cd organic matter. Fertilization application had no effect on form of soil Pb and Cr. Correlation analysis showed that there was a very significant negative correlation between pH and DTPA-Cd, DPTA-Pb. SOM and available phosphorus were significantly positively correlated with the content of DTPA-Pb and DTPA-Cd. Other factors and DTPA-Cd did not reach a very significant level. The decrease of soil pH, the increase of organic matter and available phosphorus content significantly increased the soil available Cd and Pb content.When the equilibrium concentrations of Cd in soil solution were very low(5 100 mg/L), the purple soil adsorption capacity increased rapidly with increase of Cd concentration. At this time, the adsorption was mainly realized by specific adsorption, and adsorption rate is very large. When the initial concentration became more than 100 mg/L, the adsorption capacity continued to increase but the rate tended to be gentle. The initial concentration of Cd from 5mg/L to 1000mg/L, the adsorption rate of each treatment from more than 98% turned down to 30%~40%. When the initial concentration of Cd solution was 850 mg/L, the adsorption of NPKM,(NPK)1.5S,(NPK)Cl S treatments reached the highest, were 7821mg/kg, 6759mg/kg, 6938mg/kg. When the initial concentration of Cd solution was 1000 mg/L, the adsorption of CK, NK, NPK treatments reached the highest, were 7219mg/kg, 8155mg/kg, 7870mg/kg. CK treatment and NPKM treatment fited for the Langmuir model best, and the rests fited for Freundlich best. In the process of Langmuir fitting, the maximum adsorptions were consistent with the actual value, and only(NPK)SCl was higher than the actual value. Correlation analysis showed that only KF was significantly positively correlated with soil pH, and the other factors were not significant. Desorption increased rapdly with increase of Cd adsorption in each treatment and two parabolic could describe the relationship between adsorption and desorption. Among them, the maximum desorption rate was(NPK)SCl treatment, who was 13.95%, and the lowest desorption rate was NK, who was 10.07%.In summary, long-term-fertilization affected the accumulation of heavy metals in soil, the form and availability. Long-term-application of P fertilizer and organic fertilizer significantly increased the soil heavy metal Cd, Pb, Cr accumulation. Clfertilizer application reduced soil pH, reduced the adsorption capacity of heavy metals to the soil, increased the content of soil available heavy metals and the bioavailability of heavy metals. There was a large difference in the ability of heavy metals accumulation in rice and wheat. The accumulation ability of wheat was much lower than that of rice. In the case of potential pollution of heavy metals in paddy field, the pollution risk of heavy metals to grain crops can be reduced by changing the way of crop rotation. |
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