Study On Effect Of Different Fertilizers On Available Cd Under Waterlogged Conditions

In order to tackle the problem of Cd pollution in paddy soils, investigate soil available Cd as affected by different fertilizers and offer technical support for pollution free rice production. Incubation experiments were carried out to study the effect of different N, P and K fertilizers and pH by adding acid or base on soil available Cd under waterlogged condition; Water pot experiments were carried out to study the distribution law of Cd in different organ of paddy rice; Soil pot experiments were carried out to study the Cd uptake by paddy rice as affected by different N, P, K fertilizers and two amendments. The main results were achieved as below:1. The results of incubation experiments revealed that soil pH increased sharply after the soil was flooded, especially at the beginning of incubation, and gradually decreased with incubation time and finally tended to approach the neutral values. The patterns of soil pH change were just opposite to those of soil available Cd, a negative correlation observed between the two. Soil flooding made the soil available Cd drop by 58.2%～84.1%. There were significant differences between different fertilizer types/varieties on soil available Cd, being most complex with N fertilizers and followed by K and P fertilizers. Among the fertilizers studied, ammonium chloride showed the unique ability in reducing soil pH and enhancing soil available Cd, and urea, single super phosphate and potassium chloride also promoted to a lesser extent amounts of Cd extracted from the soil. Ammonium sulfate, potassium sulfate and mono-ammonium phosphate significantly decreased soil available Cd compared to the CK treatment. Whether or not the soil was flooded, soil available Cd was highly negatively correlated with soil pH after adding acid or base (R=-0.994 without incubation and R=-0.919 after incubation for 60d). The results further suggest that in the Cd polluted paddy soil, use of ammonium chloride should be avoided, S bearing fertilizers in combination with alkaline materials can be adopted, and the rice field should be flooded all the time during growing season, all the these practices can effectively lower soil available Cd.2. The results of water pot experiments revealed that there were not significant differences between different rates of Cd treatments on the growth of paddy rice. But the centent and accumulatiom of Cd in the root and plant of paddy rice were more significantly increased with increasing addition of Cd. The content and accumulatiom of Cd in the root of paddy rice were higher than plant's, the content of Cd in the root of paddy rice were 6～9 times higher than the plant's, and the accumulatiom of Cd in the root of paddy rice were 2～3 times higher than plant's. The accumulatiom of Cd in the root of paddy rice accounted for 73.8% of all Cd uptake of paddy rice with the treatment Cd 0.3mg·L^-1, which were highest in all treatment.3. The results of soil pot experiments revealed that the yield and biomass of paddy rice were highest with the treatment of urea, calcium superphosphate and potassium chloride, and were increased with improving the rate of urea; the yield and biomass of paddy rice were lower than other treatments by the treatment of ammonium nitrate or potassium nitrate. There were no significant differences between different amendments on yield and biomass of paddy rice. Among the nitrogen fertilizers studied, ammonium chloride and high rate of urea showed the unique ability in enhancing Cd uptake by paddy rice; the other nitrogen fertilizers were equivalent. Among the phosphate fertilizers studied, the Cd uptake by paddy rice by the treatments of two phosphate fertilizers including NH₄⁺ was higher than the treatment of calcium superphosphate, and was more significantly increased with increasing content of NH₄⁺, the contents of Cd in plant by the treatment of dianmmonium phosphate were 1.4 times higher than the treatment of monoammonium phosphate. Among the potassium fertilizers studied, potassium sulfate showed the unique ability in reducing the Cd uptake by paddy rice. Among two amendments studied, Cd uptake by paddy rice with peat was not significant, but lime treatment showed the unique ability in enhancing the Cd uptake by paddy rice.Therefor, the Cd contents of rice could be lower than the Cd limited amoumt index of our country by using low-concentrating varierties of paddy rice and special water and fertilizer management on the Cd contaminated paddy soil. Keeping waterlogged condition during all growth period of paddy rice could keep high pH and reduce available Cd, also could make S^2- and Cd²⁺ formed CdS, which reduced Cd uptake by paddy rice. Avoiding applying ammonium chloride and high rate of urea on the Cd contaminated paddy soil. Applying suitable rate of urea and fertilizers including S with lime could reduce Cd uptake by paddy rice.