Yutaka Onikura

Organic acids in a flooded soil receiving added rice straw and their effect on the growth of rice

Abstract The plow layer of a flooded soil is generally characterized by low redox potential and low oxygen tension. Under such conditions, organic acids are known to be produced by the anaerobic decomposition of organic matter (3, 4, 9–11, 16–19, 21, 24, 26). Rice plants grown in pady fields, especially in poorly drained ones, might be subject to the toxic effect of reduced products. The organic acids accumulated in the soil would inhibit nutrient uptake by rice plants.

Montmorillonite in a Volcanic Ash Soil

Abstract Many kinds of volcanic ash soil distributed in Japan are usually high in humus content, consequently very dark or nearly black in color, light, loose and very friable. They have also a marked allitic property owing to the relatively large contents of allophane and aluminium hydrous oxide which strongly bind with phosphate ion.

Factors relating to labile phosphate levels in volcanic ash soils

Abstract The low availability of phosphatic fertilizer owing to the fixation of phosphorus in acidic volcanic ash soils has been noticed by many soil scientists in Japan. However, in spite of the early recognition, few studies have recently been made to obtain fundamental information on the phenomenon. It has been thought that a large amount of dressed phosphates are precipitated by soluble cations, especially by aluminum ion, or physicochemically sorbed hy the absorbing complex of volcanic ash soils where allophane and sesqui-hydroxides play major roles in the phosphorus fixation.