Nitrogen Mineralization of Silk Waste Applied to Soil under Aerobic Conditions

概要

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Silk waste which is a byproduct of silk reeling consists mainly of silk proteins such as sericin and fibroin. Although silk waste has a high N content (164 g kg^<-1>) and low C/N ratio (2.16), net N mineralization in soil at 30℃ under aerobic conditions was very slow (21.4% in 184 d). The N mineralization rate of silk waste applied to soil after hydrolysis with HCl was higher than that of untreated silk waste. The effect of hydrolysis with 0.2 M HCl for 60 min at 97℃ on the net N mineralization for 56 d was twice as high as that with 1 M HCl for 60 min at 97℃. Molecular mass distribution of silk proteins shifted to the lower range by hydrolysis, whose effect with 1 M HCl was more pronounced than that with 0.2 M HCl. The content of the crystal region in silk protein was estimated to be approximately 45% based on the relationship between the reaction (acid hydrolysis) time and the weight of insoluble residues. X-ray diffraction patterns of these residues showed that the crystal structure persisted until at least 180 min after hydrolysis with 1 M HCl at 97℃. These results suggest that crystal regions and the scattered distribution in silk proteins inhibit the decomposition of silk waste in soil. Silk waste could thus be utilized as slow-release fertilizer.
社団法人日本土壌肥料学会の論文