Study on weathering that alleviate soil acidification due to atmospheric nitrogen deposition

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Atmospheric nitrogen deposition causes soil acidification but soils have various acid buffer reactions. We aimed to examine contribution of weathering and supplies of base cations owing to litter decomposition based on changes in nitrogen dynamics, acid production, and buffering reaction due to reaping understory vegetation under Japanese cedar (Cryptomeria japonica). Reaping understory vegetation decreased in uptake of nitrogen and water. Increase in soil temperature owing to reaping (about 2℃ higher in reaping area than in un-reaping area) affected on activities of mineralization of organic nitrogen and subsequent nitrification. This was also a cause of increases in nitrogen leaching. In addition, increase in supplies of dissolved organic carbon from 0 horizon(Litter layer)due to increase in soil temperature also affected on activities of mineralization and nitrification.Increases in nitrogen leaching made increase in acid production due to nitrogen transformation. This acid production had the highest correlation coefficient between silica mobilization and its explanatory factors. Strontium isotope ratio (^<87>Sr /^<86>Sr) was negatively proportional to silica concentration. Since minerals have lower^<87>Sr/^<86> Sr, compared rainfall and plants or soils, weathering should contribute to acid buffering reaction. We also analyzed^<87>Sr/^<86>Sr of extracts, which analysis for total and exchangeable calcium (Ca) contents in O horizon. The ratio increased from Oi horizon (not decomposed litters) to Oe horizon (humified litters). It suggested that increase in exchangeable Ca in litter accompanied with decrease in litter weight would be ascribed to not only transformation from non-exchangeable form but to Ca in rainfall. Since supplies of calcium from 0 horizon alleviate soil acidification, we should try to examine relationship between weathering and supplies of Ca.