島根県奥出雲町の造林地土壌の理化学性への火入れの影響

Slash and burn land preparation for reforestation has been conducted in Okuizumo region, Shimane for more than２０years. In the present study, we investigated the effect of the burning on the soil physicochemical properties considering with passage of time after burning in forest plots with different years passed after the burning in this region. We also conducted a pot experiment to study the relationships between the soil with different years passed after the burning and soil course structure, and plant productivity. Soils were generally very porous with course pore spaces with solid phase volume less than ４０％, except for sub soils of S１５and S５sites. C/N ratio was relatively small in S５and K１, and was large in K３. Available P content was high at the surface soil in all sites. It was high in the order of K１＞K３＞S５＞K１１＞S１５＞S１１and was more than１２０mg kg−１in the sites of andisol and S５. It was suggested that avail. P level decreased as the time passed after the burnig. In the pot experiment with Komatsuna, K１１, S５, K３, K１that had relatively high avail. P, exchangeable cations, total C and N contents showed better plant growth than the others. However, Komatsuna growth was correlated with not only the nutrients of NPK, but also development of soil course structure. Komatsuna growth was the biggest in K１１ and S５where relatively long period had passed. In these sites, soil course structure started to re?develop from soil disturbance during red radish cultivation（１cropping season）associated after the burning. From these results, it was suggested that the passage of time after the burning influenced on plant growth through not only soil chemical properties change, i.e. soil fertility, but also soil course structure development.