Role of Inorganic Soil Constituents in Selected Topics

Abstract

Three topics are introduced to exemplify the important roles of inorganic soil constituents-the effects of tsunami on soil in Japan in 2011, the dynamics of radiocesium in the soil environment, and phosphates related to a soil-plant system. With respect to tsunami inundation into paddy field soils, soil erosion by seawater flow, sedimentation of soil transported by the seawater flow, precipitation of evaporites, and sodification are discussed. Removal of the deposited sediments and soil washing by rain and irrigation water were effective for restoration of the salt-affected farmlands. Radiocesium was effectively trapped by soil, which regulated its transfer to agricultural products. Among inorganic soil constituents, weathered biotite has a high fixation capacity for radiocesium. The biotite might have been released from granitic rock and volcanic ash. Apatite is the key phosphate in both natural and farmland soils, although it is converted to more soluble forms in the fertilizer industry. Fixation of phosphate by active Al materials is so high in Andisols that the recovery of phosphate by agricultural crops is low, and phosphate accumulation in plow layer soil is continuing. Struvite plays a role in cycling phosphate in the soilplant system of farmlands.