Nitrogen mineralization of silk waste applied to soil under aerobic conditions

Abstract

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-I) and low CjN ratio (2.16), net N mineralization in soil at 30"C under aerobic conditions was very slow (21.4% in 184 d). The N mineralization rate of silk waste applied to soil after hydrolysis with HCI was higher than that of untreated silk waste. The effect of hydrolysis with 0.2 M HCI for 60 min at 9TC on the net N mineralization for 56 d was twice as high as that with 1 M HCI for 60 min at 9TC. Molecular mass distribution of silk proteins shifted to the lower range by hydrolysis, whose effect with 1 M HCI 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 HCI at 9TC. 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.Key Words: crystallinity, N mineralization, silk waste, slow-release fertilizer.Silk waste is a byproduct of silk reeling and a residual part of cocoon. It mainly consists of silk proteins such as sericin and fibroin, whose N content is very high, and it could be utilized as N fertilizer. It is expected however that, since fibroin is characterized by a hydrophobic crystal structure of stacked polypeptide chains (Lucas and Rudall 1968), the decomposition of silk waste in soil is different from that of other noncrystalline biomaterials.An organic material with a lower CjN ratio is more decomposable in soil than that with a higher CjN ratio when subjected to the same conditions (Janssen 1996). N mineralization rate of plant residues is adversely affected by the lignin and polyphenol contents as well as low N content (Vallis and Jones 1973;Sivapalan and Fernando 1985;Fox et al. 1990;Palm and Sanchez 1991;Oglesby and Fownes 1992;Constantinides and Fownes 1994). Although silk waste consists mainly of protein and has a lower C/N ratio, it is decomposed more slowly, since the crystal structure of silk protein makes the silk waste resistant to decomposition.In this study, the N mineralization pattern of silk waste in soil was examined under aerobic conditions. In order to analyze the mineralization pattern, silk waste was hydrolyzed 234 A. MURASE and K. YONEBAYASHI with dilute HCl to decompose the molecular structure and the physicochemical properties of original silk waste and hydrolyzed residues were investigated. MATERIALS AND METHODSSilk waste sample. Silk waste was provided by SILK KOGEl Co., Ltd., Kyoto, Japan (Fig. 1). Pupae were separated from silk waste (cocoons). The content of the pupae in the silk waste was approximately 40%.N content and C/N ratio. Nand C con...

Multilayer Silk Sericin-Based Coating for Controlled Release of Water and Nutrients in Soil: Development, Characterization, and Performance Evaluation in Agricultural Production Model

“…It could be suggested that, from this week onward, the multilayer coating tended to release this nutrient more easily. However, it is also possible that these forms of nitrogen are associated with protein degradation in soil [54].…”

“…It could be suggested that, from this week onward, the multilayer coating tended to release this nutrient more easily. However, it is also possible that these forms of nitrogen are associated with protein degradation in soil [54]. After studying the cumulative amounts of leached nutrients (Figure 10C,D), it was established that the coating was able to reduce the amount of NPK and inorganic nitrogen leached from week 1.…”

“…In particular, the root-shoot ratio for CS + CF was lower than that for SC + F. This result proves the capacity of the coating to increase not only the soil moisture but also the nitrogen availability. An increase in this element is obtained when the SS present in the coating degrades, thereby increasing the presence of nitrates [54].…”

Application of silk waste to planting of bulbous plants in construction byproduct.

“…Silk waste is a byproduct from silk reeling and is a residual part of the cocoon. Although silk waste has a high N content, its N mineralization in soil is much slower than those of other biomaterials because it has the crystal structure of silk protein, and thus it can be utilized as a slow-release fertilizer (Murase & Yonebayashi, 2001).…”

“…Nutrient release of polyolefincoated fertilizer depends on the reaction of the coating component to physical factors such as temperature and the process of diffusion (Gandeza et al, 1991). Silk waste is decomposed and mineralized by soil microbes (Murase & Yonebayashi, 2001).…”