Diffusion of Phosphorus as Related to Soil Texture and Plant Uptake1
- S. R. Olsen and
- F. S. Watanabe2
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 Dp 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 × 10-7 to 6.7 × 10-7 cm.2 per sec. and the b value increased from 110 to 178.
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