Abstract
An effect of application of silk waste to planting of Pinus thunbergii in devastated land was investigated. Silk waste is a byproduct of silk reeling and mainly consists of silk proteins. Although the silk waste have high N content (about 13%), net N mineralization in soil was very slow. When the planting ground of broken granite was prepared on 13 November 1998, silk waste was applied into the planting ground at a rate of about 65 g N tree-1. On March 1999, young trees of Pinus thunbergii about 30 cm in height were planted at intervals of 0.8 m. At 26 months after planting, the thickening growth at the plot with the silk waste was 32% higher than that with the compound fertilizer, which was commonly applied at revegetation sites. The concentration of inorganic N (NO3--N and NH4+-N) at the plot with compound fertilizer was less than 3.5 mg kg-1 throughout the experimental period, while that with the silk waste was more than 8.7 mg kg-1 except in winter. The undecomposed residue of the silk waste remained in the ground at 30 months after application. The roots of Pinus thunbergii elongated into the silk residue. These results suggested that a large amount of N can be applied at the one time without the salt damage by the application of silk waste before planting.
