Mineral chemistry and kinetic approach to the effects of heavy fertilization and acid rain on the soil environment

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Soil acidity is one of the most serious environmental stresses that limit the root growth of many crops. Effects of heavy application of fertilizers and acid rain on the soil environment were studies from the viewpoint of both mineral chemistry and kinetic approach. Following results were obtained : 1) The rates of acidification of nonallophanic Andisols due to acid inputs from fertilization and precipitation of acid rain were much higher than those of allophonic Andisols. However, even in allophanic Andisols strong acidification was also found and aluminum toxicity was found in the roots of barley under those conditions. 2) KCl extracted Al from Fuji allophanic tea garden soils were partly originated in an organic pool and the remains were in amorphous aluminum sulfate precipitates and / or gibbsite. 3) Acidification of Andisols was reduced and thus Al toxicity of crops was alleviated by using both low acidulent fertilizer and controlled release fertilizers. 4) Mechanism of amelioration of Al toxicity by silicate fertilizers in acid Andisols was clarified to be due to the increase in soil pH rather than to the increase of silicon concentration in soil solution. Effects of phosphogypsum applied in the topsoil on the amelioration of subsoil acidity were also demonstrated. 5) Acidification of Japanese cultivated Andisols and significance of exchange acidity in their classification were examined with special reference to soil colloidal composition.