Nitrate Adsorption in Some Andisols Developed under Different Moisture Conditions(Soil Chemistry and Mineralogy)

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Nitrate leaching from agricultural lands is one of the most critical problems related to both environmental quality and human health. Although in many studies surface-charge properties of and nitrate adsorption in soils have been analyzed in tropical and subtropical regions, fewer studies have been conducted on the nitrate-retention properties of allophanic Andisols. The objectives of the present study were to examine the potential nitrate adsorption capacity and the factors affecting nitrate retention in topsoils and subsoils of three Andisols in Tokachi, Hokkaido. Nitrate adsorption at pH 6.0 was found to be low or negligible even in the subsoil of a Haplic Wet Andisol (Melanaquands), despite the high clay content. Nitrate adsorption maxima calculated from the Langmuir equation were higher in the lower horizons of a Haplic Andisol (Melanudands) and a Low-humic Andisol (Hapludands), which were developed under moderate to moderately dry moisture conditions and displayed a high allophane content and a low total carbon content. The nitrate adsorption of the allophanic Andisols was much higher than that reported from other studies conducted in Ultisols and Oxisols, which are rich in iron oxides. The potential capacity to adsorb nitrates and retard nitrate movement should be taken into account in predicting the fate of nitrate in soils and the consequent mitigation of groundwater contamination.
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