Abstract
Fertilizers coated with polyolefin resin are characterized by controlled release rates of nutrients, and are leading to improved fertilizer-use efficiency and reduced labor. However, the coating material remains as a residue in the soil after the release of nutrients. In the present study, a new coating material was developed by adding polyolefin resin (SGS) including 2% Feacethylacetonate and 0.2% Ni-dibutyldithiocarbamate in order to promote light oxidation of the coating material and its biodegradation. The patterns of release of nutrients into water from fertilizer coated with SGS-polyolefin, were similar to the nutrient release patterns from coated fertilizer without SGS addition. Similar nutrient release patterns from the coated fertilizers with and without SGS were also observed when fertilizers were either applied to the surface of soil with or without 50% shading, or embedded in soil. These results indicated that addition of SGS did not affect the patterns of release of nutrients. The fertilizer coated with SGS-polyolefin was found to be broken down easily after a one-year exposure to natural light and the proportion of compounds having less than 3,000 molecular weight was increased to 38%, which was twice that of the fertilizer without SGS. During a 39-month exposure to natural light, the peak molecular weight of polyolefin with SGS decreased from 35,500 to 1,700,indicating strongly that addition of SGS polyolefin promoted the light oxidation and subsequent decomposition of polyolefin. Bacteria were screened from Japanese soils using 34-month exposed SGS-polyolefin resin as a sole carbon source. Nine species of bacteria were isolated and identified as Pseudomonas sp., Sphingomonas sp. and Acinetobacter sp. Only the compounds with molecular weights less than 3,000 in SGS polyolefin were utilized by these bacteria as a sole carbon source. From these results, the maximum concentration of residual coating material with SGS polyolefin in soil was estimated to converge to 0.63 kg m^<-3> after 120y, under the typical condition of cultivation.
