Phosphorus Diffusion in Soils: I. The Effect of Applied P, Clay Content, and Water Content

Abstract

Abstract Self‐diffusion coefficients of 32 P ( D ) were measured in four soils: Miller clay, Norwood loam, and two textural intergrades of these two soils. Clay percentages of the soils were: Norwood, 12.5; Intergrade I, 25.0; Intergrade II, 36.0; and Miller, 59.0. The P rates used were 0, 25, 50, and 100 ppm. The moisture levels were 35, 60, and 100% of the water content between ⅓ and 15 bars tension. The D values averaged over all clay and P levels, increased from 10.25 × 10 ‐10 to 27.76 × 10 ‐10 cm 2 /sec as the water content increased from 35 to 100% of the available moisture. The average D value increased from 5.05 × 10 ‐10 for the Norwood to 26.59 × 10 ‐10 cm 2 /sec for the Miller soil. Likewise, D values increased with increasing rates of added P for all soils. The data indicated reduction in available water has less effect on diffusion rates of P in clay soils than in the lighter‐textured soils. It follows that in order to maintain a given rate of diffusion in a soil, as water content decreases, the amount of added P must be increased.