Amelioration of subsoil acidity in a nonallophanic andosol by surface application of organic calcium salts

The effects of surface application of organic Ca-salts on the amelioration of the subsoil acidity in a nonallophanic Andosol distributed in Hiroshima Prefecture were studied by a model experiment with columns. Consequently, the effects of inorganic Ca-salts were also examined compared with those of organic Casalts. Topsoil treatment with carbonate and nitrate did not lead to a substantial amelioration of the subsoil acidity. In the sulfate treatment, approximately 64% of Ca applied to the topsoil was distributed uniformly in the 10-50 cm subsoil layers after the 20th irrigation (800 mm as rainfall). However, there was a large amount of exchangeable Al in the subsoil and the subsoil pH was obviously lower than that of the control. Thus, these three inorganic Ca salts were unsuitable for ameliorating the subsoil acidity in the nonallophanic Andosol used in this study. In the EDTA, citrate, and acetate treatments, Ca was distributed in the subsoil though its content decreased with the soil depth and the total amount of Ca distributed in the 10-50 cm subsoil layers was approximately 63, 44, and 55% of that applied to the topsoil, respectively. In addition, almost all of the Ca distributed in the subsoil was in an exchangeable form. In the EDTA treatment, the subsoil pH exceeded 6.0 and the amount of exchangeable Al was very low. Although citrate and acetate are not as effective as EDTA, these Ca-salts also led to a decrease of the content of exchangeable Al in the 10-50 cm subsoil layers and to an increase of pH in the 10-30 cm subsoil layers.