Abstract
The effect of three nitrogen carriers and calcium silicate on the uptake of native bound soil phosphates from a Jamaican latosolic soil was investigated using maize as the indicator plant. Small but significant releases of native bound P were obtained by the application of high rates of ammonium sulphate, whereas similar rates of urea and calcium nitrate had no effect on phosphate uptake. Application of calcium silicate had a beneficial effect on the uptake of phosphate by the plants. Phosphate absorption by maize seedlings on two soils was also investigated using three phosphate fertilizer sources: (i) commercial triple superphosphate, (ii) finely ground tricalcium phosphate and (iii) an insoluble P product designated 'Red Mud Fertilizer-phosphate' (RMF-P), prepared by reacting triple superphosphate with a residue ('Red Mud') from the bauxite factories. In the highly acid soil (Linstead clay loam, pH 4·5) the relative effectiveness of the triple super-phosphate was somewhat lower than in the neutral bauxite oil (pH 7·1). The RMF-P and tricalcium phosphate were superior to the triple super-phosphate in the acid soil. However, in the neutral bauxite soil the converse was true. There was little or no difference between the effectiveness of the RMF-P and tricalcium phosphate on both soils. Some of the implications of using lightly soluble phosphatic fertilizers (in preference to the current highly soluble P fertilizers) on high phosphate-fixing latosolic soils are discussed.
