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FACTORS INFLUENCING THE ISOTOPICALLY EXCHANGEABLE PHOSPHATE IN SOILS: PART II. THE EFFECT OF BASE SATURATION WITH SODIUM AND CALCIUM IN NON-CALCAREOUS SOILS

P. ARAMBARRI and O. TALIBUDEEN
Plant and Soil
Vol. 11, No. 4 (November 1959), pp. 355-363
Published by: Springer
Stable URL: http://www.jstor.org/stable/42931820
Page Count: 9
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FACTORS INFLUENCING THE ISOTOPICALLY EXCHANGEABLE PHOSPHATE IN SOILS: PART II. THE EFFECT OF BASE SATURATION WITH SODIUM AND CALCIUM IN NON-CALCAREOUS SOILS
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Abstract

The effect of base saturation of non-calcareous soils with sodium and calcium on their total labile phosphate was studied in solutions of sodium and calcium chlorides of the same ionic strength (μ = 0.02). The total labile phosphate in 6 out of 7 soils was between 8 to 40 per cent higher in sodiumsaturated soils than in calcium-saturated soils. A much larger part of the total labile phosphate was found in solution in the sodium-saturated soils.The ratio of phosphate in solution in these soils to that in calcium-saturated soils varied from 3.4 to 8.1 with a mean value of about 5.5 as compared with a theoretical value of 4.1. A method is suggested for obtaining 'corrected' values for the abnormally high phosphate concentrations in solution from sodium-saturated soils. 'Corrected' values give smaller differences between the total labile phosphate in sodium and calcium forms of these soils. Rates of isotopie exchange of the more slowly exchanging forms of soil phosphate were measured at 25° and 35°C for the sodium-and calciumsaturated forms of one Rothamsted soil. At 25°C these rates were four times higher in the sodium-saturated soil than in the calcium-saturated soil although the total labile phosphate in the two forms was the same. Increasing the temperature to 35°C doubled these rates of exchange in the sodiumsaturated soil but had no effect on the calcium-saturated soil. This suggests that the cation-exchangeable calcium is strongly linked to the slowlyexchanging forms of phosphate in the soil. No differences were observed in the rates of isotopie exchange of phosphate in this soil after calcium saturation with either 0.01 molar or 1.0 molar calcium chloride. The precipitation of calcium phosphates during the calciumsaturation procedure could not therefore be responsible for the observed differences between sodium-and calcium-saturated samples.

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