Effect Of Coating Materials For Slow/Controlled Release Fertilizer On Soil Ecology

Residues of coating materials for slow/controlled release fertilizer may lead to environmental risk in case of years of the continued use of slow/controlled release fertilizer. In this paper, two kinds of typical coating materials for slow/controlled release fertilizer and three categories of soil located in major grain producing areas in China were employed. Greenhouse pot experiments and field in-situ experiments were conducted to investigate the effects of typical coating materials for slow/controlled release fertilizer on soil physical and chemical properties, soil microbial biomass carbon and microbial biomass nitrogen, community structure of soil fauna, and crop seedling growth as well as the cell ultrastructure of the root. It was discussed that the soil ecological dose effect and influence on soil quality, preliminary revealed soil ecotoxicological mechanisms of typical coating materials for slow/controlled release fertilizer. The main results were as follows:1. No significant effects were observed on the pH value and organic matter (OM) content of black soil for the continued accumulated resin and water-soluble polymer coating materials.20and50years accumulation of water-soluble polymer coating materials and20years accumulation of resin coating materials significantly reduced the OM content of fluvo-aquic soil by12.1%,11.1%and10.4%compared with the control (p<0.05). The pH value of paddy soil reached2.7%higher than that of the control (p<0.05).2. The effects of two kinds of coating materials accumulated following different years on soil microbial biomass carbon and microbial biomass nitrogen (MBC, MBN) of black soil, fluvo-aquic soil and paddy soil were not identical. No significant effects were observed on the MBC and MBN content in the black soil for the accumulation of coating materials in0to50years. The accumulation of water-soluble polymer coating materials in50years significantly decreased the MBC and MBN content of the fluvo-aquic soil by23.5%,20.3%compared with that of the control (p<0.05). The MBN content of the paddy soil were significantly reduced by56.6%and61.3%respectively due to the accumulation of resin and water-soluble polymer coating materials in50years (p<0.05). Two kinds of coating materials with recommended nitrogen application levels had significantly different impacts on the MBC and MBN content of black soil in the period of maize seedlings, which were increased by17.8%and29.7%respectively under the treatment of resin coating material, and decreased by3.6%and32.9%respectively under the treatment of water-soluble polymer coating material.3. The individuals and groups of soil fauna were increased during the crop growth period. The composition of the soil meso-microfauna was relatively stable, while macrofauna were susceptible to external environment, belonging to the class of environmentally sensitive soil organisms. The accumulation of the resin and water-soluble coating materials in0to50years increased the individuals of the black soil and the fauna of the paddy soil. The individuals of paddy soil macrofauna reached at the maximum and that of meso-microfauna were4.6and4.3times as that of the control respectively due to resin and water-soluble coating materials during the maturity of rice.4. Both kinds of coating materials entering cropland with nitrogen application increased the individuals and groups of black soil macrofauna and meso-microfauna. Groups of macrofauna were significantly increased by16.7%～66.7%(p<0.05). Coating materials entering cropland with recommended nitrogen application obviously increased the individuals of black soil meso-microfauna by90.6%and156.5%respectively under the treatments of resin and water-soluble polymer coating materials in September. The evenness index of the black soil macrofauna and the diversity index of the black soil meso-microfauna reached at the highest in July. Similarity index (q index) of black soil meso-microfauna generally higher than that of macrofauna, which indicating more common groups of meso-microfauna among treatments and reflecting coating materials had lesser impact on meso-microfauna community composition. The correlation analysis among the fauna community structure and soil physical and chemical properties showed that groups of macrofauna were significantly positive correlated with the pH value and OM content of black soil (r=0.691, r=-0.984, p<0.05). Principal component analysis demonstrated that a certain dose-effect relationship existed between water-soluble polymer coating materials and the soil fauna community structure, and the relationship varied with the time.5. The coating materials strongly affected seedling root growth. Root morphology analysis indicated that the accumulation of resin and water-soluble coating materials in50years inhibited maize root growth, the total root length were decreased by51.8%,47.6%respectively, total root surface areas were decreased by49.9%,41.0%respectively. Certain promoting effect on the growth of rice root were observed because of the accumulation of two coating materials in20years, total root length were14.71%,7.55%respectively, higher than that of the control. Both kinds of the coating materials showed a certain inhibition for maize and rice root vigor, which were more obvious at low concentrations. Compared with the control, the accumulation of resin coating material in5years reduced maize root vigor by44.1%, and rice root vigor were decreased by90.8%and85.3%respectively under the treatment of the accumulation of resin and water-soluble coating materials in10years.6. Maize and rice root tip cells were damaged by resin and water-soluble coating materials, including different degrees of plasmolysis, damaged membrane system (mitochondrial membrane damage, plasma membrane breakage), cell wall deposits, well-developed endoplasmic reticulum, phenomenon of phenolics gathered, etc. Among which, well-developed endoplasmic reticulum, phenomenon of phenolics gathered were reflection of maize and rice seedling stress resistance mechanisms. The accumulation of resin and water-soluble coating materials in50years seriously damaged nuclei of maize root tip cells, including nuclear deformation.In conclusion, the fluvo-aquic soil was the most vulnerable soil to coating materials for slow/controlled release fertilizer, followed by the paddy soil, and lastly the black soil. A certain dose-effect relationship existed between water-soluble polymer coating material and the black soil fauna community structure. The coating materials had a great influence on the growth of crop seedling. It should be noted that the influence of residues of coating materials for slow/controlled release fertilizer on the fluvo-aquic soil and crop seedling in agriculture production.