Abstract
The relationship between soil acidification and nutrient-retention capacity was examined for soils in the volcanic-ash derived tea fields located in the Oosumi Peninsula of Kagoshima Prefecture. The following results were obtained. 1) The total carbon content of soils showed a positive correlation with the cultivation length of tea fields. This is due to accumulation of organic matter as a result of the long history of application of organic residues. 2) CEC (pH 7.0) showed a positive correlation with the total carbon content; therefore, increase of CEC (pH 7.0) was ascribable to an increase of organic substances. 3) CEC (field pH) ranged from 9 to 17 mol_c kg^-1 and was equivalent to 19 to 61% of CEC (pH 7.0). 4) The difference between CEC (pH 7.0) and CEC (field pH) became larger with the extent of acidification of soils. 5) The content of water-soluble bases was higher in the more strongly acidified soil, leading to the easier leaching of bases to lower layers. 6) Reclamation of soil pH to 4.5 was indispensable to maintaining the retention capacity for ammomum. The present results suggest important practices for the long-time plant-nutrient and soil management of tea fields in the volcanic-ash soil area.
