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Diffusion of Phosphorus as Related to Soil Texture and Plant Uptake¹

ABSTRACT

Differences in the diffusion coefficients of phosphorus (P) between sandy and clay soils were applied to explain variations in rates of P uptake by corn seedlings from equal initial concentrations of P in the soil solution. The relation between labile P of the solid phase and P concentration in solution or the phosphate capacity, also varies with the clay content. An equation relating uptake of P by plant roots to the diffusion coefficient and the phosphate capacity showed that the rate of uptake was proportional to
where D_p is the diffusion coefficient and b is the slope of the line relating labile P to concentration of P in solution or the phosphate capacity, when other factors are constant. The equation predicts that the rate of uptake of P will be one-third as much from the sandy soil as from the clay soil at equal concentrations of P in the soil solution. Actual measurement of the rate of P uptake by corn seedlings agreed closely with the predicted values from the equation for P concentrations < 0.2 ppm. As the clay content of three soils increased from 17 to 51%, the diffusion coefficient for P increased from 1.1 x 10^-7 to 6.7 x 10^-7 cm.² per sec. and the b value increased from 110 to 178.

¹ Contribution from the Soil and Water Conservation Research Division, ARS, USDA, and the Colorado Agr. Exp. Sta., Fort Collins, Colo. cooperating. Scientific Journal Series 821. Presented at the meeting of Div. II, Soil Science Society of America, Cornell University, August, 1962.

² Soil Scientists, Northern Plains Branch, Agricultural Research Service, USDA, Fort Collins, Colo.

Received for publication January 23, 1963. Accepted for publication April 15, 1963.