Potassium and Ammonium Taranakites, Amorphous Aluminum Phosphate, and Variscite as Sources of Phosphate for Plants

Abstract

Abstract As shown by the response of three successive crops of corn, the effectiveness of potassium and ammonium taranakites as sources of phosphorus increased with prolonged contact with the soil. This effect was independent of the soil pH. Potassium taranakite was a consistently better source of phosphorus than ammonium taranakite. On acid soil, amorphous aluminum phosphate was a moderately effective source of phosphorus, whereas crystalline variscite was ineffective. On calcareous soil, amorphous aluminum phosphate, variscite, and both taranakites were as effective as monocalcium phosphate, and on this soil the particle size of the aluminum phosphate was the controlling factor in their effectiveness.