Abstract
Residual effects of superphosphate application to an Orangeburg fine sandy loam over a 36-yr. period were measured by yield and P content of crimson clover (Trifolium incarnatum) and by the P level in the soil. The amt. of available soil P (A) was detd. by the formula: [image] of P2O5 in an appln. of radioactive superphosphate, and p - % of total P in crop derived from the appln. As the soil P level increased, yield and P content of the clover increased, while the % of total P in the clover derived from the radioactive superphosphate decreased. Significant correlation coeffs. were obtained between A values and NH4F-soluble and Truog P in the soil.

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