Effects of short-rotation harvesting on soil microbial biomass and nitrogen mineralization in Gmelina arborea plantations in East Kalimantan

In order to elucidate the effects of shor t-rotation har vesting on microbial biomass and nitrogen (N) mineralization in soil, we studied Gmelina arborea Roxb. (yemane) plantations and the mixed planting of a legume cover crop in East Kalimantan. The microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) decreased by approximately 40 % to 50 % in the plantation plots than in a secondar y forest plot. The MBC increased with the stand age in the plantation plots, while the MBN remained low. In a mixed plot of yemane and legumes, the MBC, MBN, and N mineralization rate were approximately the same as those in a 10-yr plantation plot without cutting; however, these values were higher than those in a 4-yr coppice plot after the cutting of a 6-yr plantation. Mixed planting of a legume cover crop might influence the soil nutrition by N-2 fixation. The percentage of the MBN in the total N in the plantation plots was lower than that of the MBN in the total N in the secondary forest plot because the rate of decrease in MBN was higher than that in the total N due to clear-cutting and plantation.