| Soil sulfur deficiency is more serious in southern of the Yangtze River in China. Sulfur fertilizers can improve crop yields and quality, and also decrease them if applied properly. And the nutritional role of sulphur is far inferior to the effects and interaction between sulfur and other elements. Therefore, it is essential that rational application of sulfur fertilizer. Pot experiments were carried out to study effects of different sulfur fertilizers (S0-S, SO42--S) on rice, rapeseed and theirs roots vigor, capacity of nutrient uptake in red and yellow brown soils, soil oxidation-reduction reaction, soil microbial biomass C, N, S and enzyme activity and the impact of biuret on paddy soil redox and rice roots vigor. Meanwhile, we explored the effect of sulfur fertilizer on different crops in heavy metal Cd, Cu contaminated soil, and the impact of application of sulphur fertilizers single and combined phosphorus rocks on Cd, Cu forms changes. These could provide a support for the rational application of sulfur fertilizer and situ immobilization technology in heavy metal contaminated soil. The main results are described as follows.(1) A rice pot experiment was conducted at the same dose of sulfur fertilizer applied, the effective sulfur content in yellow-brown soil was relatively higher than that one in the red soil, probably because the content of Fe(Ⅲ) was higher, the oxidizing ability was stronger in yellow-brown soil. Total Fe content of the plaque of root surface in:red soil> yellow brown soil, and total sulfur absorbed by the rice in red soil more than that in yellow-brown soil, which suggested sulfur in the plaque of root surface is the base of nutrient supply. Sulfur oxidation is inhibited firstly and promoted later by sulfur application mixed with biuret during the process of soil incubation. Effect of different rates of biuret fertilizer application on the S0-S fertilizer effectivity, the effectivity was reduced in red soil while enhanced in yellow brown soil with increasing rate of biuret application according to sulfur uptake by rice. Biuret might inhibit the oxidation of the root in the plaque of root surface, and led to generate the precipitation of FeS or FeS2.(2) Sulfur oxidation rate is influenced by the different temperature and moisture in the red and yellow brown soils, the rate is very low when temperature is below5℃, and is quite fast when wet and dry of soil moisture alternated frequently. And the rate also increased with increasing rates of sulfur applied. The degree of soil redox, pe+pH, was in the range of11-12。(3) Multivariate regression analysis showed that the correlation of the soil pH, Eh and log[SO42-] in red soil is better than that of the yellow-brown soil, and reached a highly significant level. There had an negative impact on rape growth, roots vigor and absorption of S amount in the0.4g/kg SO42-S treatment of the red soil and the0.4g/kg S0-S and0.2g/kg SO42--S treatment of yellow brown soil. The redox system was H2SO3/S mainly in the0.4g/kg SO42--S treatment of the red soil and the0.2g/kg SO42--S treatment of yellow brown soil, which could generate reducing substances, which had a negative impact on rape growth. Although the redox system was H2SO4/S mainly in the0.4g/kg S0-S treatment of the yellow brown soil, the correlation between soil redox potential and the rates of sulfur apllied was not significantly(4) Rape was used as testing crop, soil microbial biomass C, N, S and soil basal respiration (CO2-C) was measured. Soil microbial biomass C, N, S and soil basal respiration increased with increasing the rates of sulfur fertilizer applied, but the soil microbial biomass C decreased in the seedling stage. The content of rape uptake sulphur in the S0-S treatment was higher than that in the SO42--S treatment, which suggested that the role of increasing yield in the S0-S treatment was better. Soil microbial biomass C, N, S, and soil basal respiration in the rhizosphere soil was lower than that in the non-rhizosphere soil, but the soil microbial biomass S was greater than that of the non-rhizosphere soil in the rape seedling stage, and the soil pH of the S0-S treratments were also similar results, which showed that soil pH was a very important factor affecting the microbial activity. The invertase and catalase activities were weaker, and urease activity was stronger in the rhizosphere soil than that in the non-rhizosphere soil. Soil microbial biomass and enzyme activities played an important role in uptaking of sulfur by rape.(5) Sulfur fertilizers and phosphate rock single applied in heavy metals Cd, Cu contamination in soil, the nepeta biomass increased in following order:phosphate rock> SO42--S>S0-S treatment. The crops biomass of sulfur fertilizers combined with phosphate rock applied was significantly higher than that of two fertilizers single applied, respectively. A double toxic effect of excessive amount of sulfur fertilizer applied on crops growth in Cd and Cu combined contaminated soil. In comparison with phosphate rock, sulfur fertilizer promoted the transformation of Cu and Cd from the inactive forms to the active ones more easily.(6) Compared with phosphate rock, different rates and forms sulfur fertilizer and phosphate rock combined application could more easily decrease the contents of water soluble and exchange forms Cu, residual Cu, Cd, and increase the contents of water soluble and exchange forms Cd. The role of0.2g/kg S0-S and phosphate rock combined treatment in promoting the transformation of Cd from the active forms to the inactive ones was better than that of the phosphate rock treatment. The contents of water soluble and exchange forms Cu, Cd decreased and residual Cu, Cd increased after continuous cultivated pakchoi and nepeta, which revealed there had a good effect of sulphur fertilizers combined with phosphate rock on the Immobilization of soil heavy metals. |
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