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Solubilization of Soil and Rock Phosphate as Related to Root Cation Exchange Capacity¹

ABSTRACT

Plants with root cation exchange capacities ranging from 10 to 60 me./100 g. dry root, were grown in greenhouse pots on B horizon Merrimac silt loam very low in available and total phosphorus. Rock phosphate at the rate of 1,000 pounds per acre was mixed throughout the soil. Plants with high cation exchange root systems (ragweed and smartweed) were more effective in obtaining phosphorus from soil and rock phosphate for themselves, and were two to three times as effective as the lower exchange root systems (Lamb's quarters and wheat) in solubilizing soil and rock phosphate for the following crop of sudan grass. Oats with relatively low cation exchange roots, when grown in association with red clover (high cation exchange roots) contained 60% more phosphorus than oats alone. Plant roots with high cation exchange capacity bond Ca with greater energy than low cation exchange roots. Two important mechanisms of P release are believed to be involved, (a) bonding of Ca by the plant root colloid to dissolve the rock phosphate crystal and (b) complexing of Al and Fe by organic anions to solubilize soil Al and Fe phosphates.

¹ Contribution No. 976 of the Massachusetts Agr. Exp. Sta., University of Massachusetts, Amherst, Mass.

Received for publication November 20, 1954.