DISSOLUTION OF PHOSPHATE ROCK IN ACID SOILS AS INFLUENCED BY NITROGEN AND POTASSIUM FERTILIZERS

The dissolution in two acid soils (Weston, pH 4.5; Davidson, pH 5.2) of phosphorus from North Carolina phosphate rock, a highly reactive rock, was decreased by additions of (NH4)2SO4or their mixtures, but increased by the addition of urea. The effect of urea was decreased by addition of KCI. It is concluded that urea hydrolyzes the organic matter of the soil and that the products of hydrolysis chelate calcium ions and so increase the dissolution of phosphorus from the rock. (NH4)2SO4and KCI, on the other hand, increase the phosphorus-sorption capacity of the soil and so decrease the water-soluble phosphorus in the soil. The results suggest that the beneficial effects of nitrogen and potassium fertilizer salts on the uptake of phosphorus by plants may result from stimulation of plant growth and not from solubilization of phosphate rock. © 1979 The Williams & Wilkins Co.