Degradation Of Controlled-Release Fertilizer Resin Coating Residual And Its Effects On Microbial Quantity And Enzyme Activity In Soils

Coated controlled-release fertilizer as a new kind of fertilizer, compared with traditional fertilizer, could significantly increase utilization efficiency of the fertilizer, reduce environmental pollution and improve crop yields and quality, have become the focus of fertilizer research quickly. As production technology matured and production cost reduction in the near future, coated controlled-release fertilizer will be widely applied to agricultural production. With the controlled-release fertilizers application, the resin coating residual of controlled-release fertilizer will be left in the soil, it will take a long time before the coating residual degradation. The potential impacts of the coating residual on the soil environment should be investigated, to provide the scientific guidance for the coating materials research.Degradability, microscopic structural changes and degradation products of resin coating residual of controlled-release fertilizer were investigated by simulate degradation, using Scanning Electron Microscope(SEM), Fourier transform infrared spectroscopy(FTIR), Solid Nuclear Magnetic Resonance(NMR) and gas chromatography-mass spectroscopy(GC-MS), the effects of controlled–release fertilizer coating residual on microbial quantity and enzyme activity in soil also were investigated by wheat-rice and wheat-corn rotated cultivation in a pool experiment. The main results were summarized as follows:1. Controlled-release fertilizer coating residual (CRFCR) was photodegradable under UV light irradiation. The results of SEM, FITR and GC-MS showed that under UV irradiate 168 hour later, the surface of coating residual was not smooth, Carbonyl Index (CI) became larger, which proved that coating residual had begun to degradation, as the time longer of UV light irradiation, the concentration of degradation products gradually increased. Some low molecular weight products, such as alkyl hydrocarbon, ketone, aldehyde, ester, carboxylic acid and binary carboxylic acid were detected in the degraded coating residual.2. CRFCR could be degradated slowly in soil. Results of SEM, FITR and GC-MS showed the surface of coating residual became rough in soil six years, Carbonyl Index(CI) became larger, which proved that coating residual had begun to degradation. Degradation products of resin coating residual were different with degradation under UV irradiation. Coating residual degradated completely needs about 36 years in moisture content of 20% silty clay loam, when environmental temperature 35℃,but degradation time will be longer in natural condition. 3. CRFCR could affect some physical-chemical characteristics of soils. The results of experiment showed that controlled release fertilizer coating residual could reduce soil bulk density, increase soil total porosity. So aerate status of soil has been improved and loose soil increased the aerate and dank character of soil, but had no effect on soil special gravity, pH, and available N, P and K.4. CRFCR had no negative effect on soil microbial quantity and soil enzyme activity, coating residual could reduce soil bulk density, increased soil total porosity reversely, aerate status of soil has been improved and loose soil increased the aerate and dank character of soil, which supply a more appropriate living environment for soil microorganism and enzyme activity, increase soil microbial quantity and enzyme activity.5. Soil microbial quantity and enzyme activity did not change regularly followed with the amount of coating residual in soil; there is no obvious correlation between soil microbial quantity and enzyme activity and coating residua, under the amount of coating residual in soil at a range of 90-360g m-2.6. Compared with CK treatment, the amounts of bacteria, fungi and actinomyces, and activities of soil urease, invertase, neutral phosphatase activity significantly increased; activity of catalase decreased. The results indicated that application of fertilizer could increase the amounts of bacteria, fungi and actinomyces, and activities of soil urease, invertase, neutral phosphatase, restrain catalase activity.