PHOSPHATE RETENTION ON SOILS IN THE CENTRAL VALLEY OF CHILE

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The retention of phosphate and the content of available phosphate were estimated by a new method with monobasic sodium phosphate(pH4.5)and the Olsen's method, respectively, on the principal soils in the central valley in Chile. Trumaos(Andosols)are, in general, distinctly higher in the value of P-retention than other soils with the exception of trumaos of alluvial origins. This characteristic of trumaos can be employed for the identification of trumaos among other soils and alluvial trumaos among ordinary ones. The P-retention value of volcanic ash soils decreases with the crystallization of the amorphous inorganic materials. According to the data of P-retention, certain rojos arcillosos(red clays)are presumed to have surface horizons of volcanic ash origins. Granitic rojos arcillosos are notably low in P-retention compared with other rojos arcillosos. The organic matter content and P-retention value of soils are closely related to each other, suggesting that both organic matter and phosphate are retained by soils on the same materials though by different mechanisms. The content of available phosphate in surface horizons varied from soil to soil and no difference was noticeable among the soil groups of trumaos, rojos arcillosos, and paddy soils. Also no relation was found between the P-retention value and available phosphate content. However, in lower horizons where plant roots are scarce or absent, no available phosphate was found in trumaos in contrast to the presence of an appreciable amount of phosphate in rojos arcillosos. Phosphates of native trumaos appear to be practically insoluble. The surface soil rich in available phosphate was limited to cultivated fields, suggesting that the available phosphate was largely due to the remnant of applied fertilizers and partly to the remains of organic phosphorus from plants and soil organisms. The content of available phosphate tends to decrease with time after application of phosphates, and a significant negative correlation coefficient was obtained between the amount of available phosphate and the P-retention value of soils at least by three months after application of phosphate. The higher the P-retention value of soils, the less the content of available phosphate, and the faster the fixation of phosphate.
社団法人日本土壌肥料学会の論文

PHOSPHATE RETENTION ON SOILS IN THE CENTRAL VALLEY OF CHILE

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