Effects of Fertilization Level on the Growth of Cryptomeria japonica Container Seedlings

Abstract

This study was conducted to elucidate the effects of fertilization level on the growth of Cryptomeria japonica container seedlings. In a basic fertilizer test, seedlings were grown under three fertilization conditions using the slow-release fertilizer A (N-P-K＝12-8-10) at 5-6, 10-12, or 20-24 g/L. Seedling height increased with increasing amounts of fertilizer added, although no differences were observed between the 10-12 and 20-24 g/L doses. In the additional fertilizer test, the effects on seedling growth were compared between three concentrations of slow-release fertilizers B (10-18-15) and C (6-9-9) at 1.5, 3.0, or 4.5 g/seedling, and a liquid fertilizer. Additional treatment with 4.5 g of fertilizer B produced the greatest increase in seedling growth, particularly diameter. Seedlings were raised under optimal conditions of base fertilization treatment (20 g of fertilizer A, 40 g of leaf mold and 4 g of magnesium lime per 1 L of soil) and additional fertilization treatment (4.5 g of fertilizer B and 0.9 g of magnesium lime per plant); this treatment produced seedlings with an average size of 36.2 cm in height and 4.8 mm in diameter one year after sowing. From this experiment, the 69％ of container seedlings grew up to reach the Japanese Forestry Agency’s 5th standard size even within one growing period, although the period for bare-root seedlings needs two years in the Japanese Kanto region. Therefore, our results demonstrate a reduction of the growth period of Cryptomeria japonica through the efficient propagation of container seedlings supplemented with the application of slow-release fertilizers.