Characteristics of the farmlands in Kochi prefecture [Japan] with special reference to physico-chemical properties, mineralogy, zero point of charge and delta p
1998
Kawazu, H. (Kochi Univ., Nankoku (Japan). Faculty of Agriculture) | Sakurai, K.
The farmlands (upland crop fields, drained paddy field for upland crops, reclamated upland field) and forested area in the vicinity were surveyed in correspondence with the Shimanto Belt, Chichibu Belt and Sambagawa Belt in Kochi Prefecture, Japan. The soil fertility in each belt was evaluated using the general and inherent properties of the soils, such as oxide contents, zero point of charge (ZPC), and clay mineralogy, which have not been often included in soil evaluation so far. Based on these data, the factors affecting ZPC and sigma(p) were extracted by statistical analysis. In the Shimanto Belt, land reclamation was conducted widely, resulting in immature soils with both poor physical and chemical soil properties. Improvement of the soils could be accomplished only by continuous soil management. The amount of Fe and Al oxides as variable charge fractions and lime application caused a higher shift in ZPC, while the higher content of organic matter and presence of permanent negative-charge clays caused a larger sigma(p). In the chichibu and Sambagawa Belts, drained paddy fields for upland crops were distributed widely. Although improvement in the permeability due to aggregation in the surface soils was observed, subsoils had not yet been improved in terms of both permeability and retention of water due to remnant properties of the former paddy fields. Exchangeable cations derived from permanent materials caused a higher shift in ZPC, while organic matter and permanent negative-charged clay caused a larger sigma(p) value, the same as the reason for the soils in the Shimanto Belt. In all the soils used in the study, the application of lime brought a higher shift in ZPC value for the surface soil, while exchangeable cations derived from parent materials made it higher in the subsoils
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