The effect of treatment for land surface during forest practice on soil nitrogen dynamics

Abstract

The inorganic nitrogen pool in soil, soil microbi-al biomass, nitrogen pool in vegetation and microbial nitrogen mineralization in soil were investigated to understand the effect of treatment for land surface by scarification on soil nitrogen dynamics in a forest ecosystem located in northern Hokkaido, Japan. The nitrate pool in the soil after scarification was higher than those in the control site during 1 ~ 3 years after the treatment, and tended to decrease with the years. The increment of the soil nitrate pool during the initial 3 years after the treatment was caused not only by the decrease of nutrient uptake by vegetation, but also by the decrease of immobilization of soil nitrogen due to the decrease of soil carbon as an energy source for soil microbes. The temporal decrease of the soil nitrate pool in the initial periods after the treatment appeared to be caused by the leaching of nitrate from soil due to the rainfall and snow melting because nitrogen uptake by vegetation was small during these periods. Uptake of nitrogen by vegetation was an important factor for the temporal decrease of the soil nitrate pool about 4 years after the scarification. Net nitrification in the soil 5 years after the scarification was still higher than that in the control site, indicating that the effect of the scarification on soil nitrogen dynamics was maintained in the studied time scales.