Nitrogen mineralization of silk waste applied to soil under aerobic conditions

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 degreesC 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 degreesC on the net N mineralization for 56 d was twice as high as that with 1 ar HCl for 60 mill at 97 degreesC, 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 m HCl at 97 degreesC. 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.