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Phosphorus Diffusion in Soils: I. The Effect of Applied P, Clay Content, and Water Content¹

ABSTRACT

Self-diffusion coefficients of ³²P (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 and 15 bars tension. The D values averaged over all clay and P levels, increased from 10.25 x 10^-10 to 27.76 x 10^-10 cm²/sec as the water content increased from 35 to 100% of the available moisture. The average D value increased from 5.05 x 10^-10 for the Norwood to 26.59 x 10^-10 cm²/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.

¹ Contribution from Texas A&M University, College Station, Tex., and the University of Kentucky, Lexington, Ky.

² Formerly Graduate Student, now Associate Principal Research Scientist, Technology, Inc., Houston, Tex.

³ Professor and Assistant Professor, respectively, Texas A&M University, College Station, Tex.

⁴ Formerly Professor, Texas A&M University, now Professor, University of Kentucky, Lexington, Ky.

Received for publication October 23, 1970. Accepted for publication January 27, 1971.