Abstract
High P retention by soil particles in a serious fertility constraints in the tropics. Changes in P-sorption characteristics of an acid-mineral soil with incubation with three lime rates (0, 100, and 200% Al saturation equivalent), three rates of coffee pulp (0, 25 and 50 g kg-1), and with heating (n’kwop) at three temperature levels (0, 250 and 500ºC) were therefore evaluated. For all treatments, P-sorption isotherms were plotted. Amount of P sorbed at soil solution concentration of 0.2 ?g P mL-1 (q0.2), Langmuir equations and derived maximum P-sorption capacity (qmax) were determined. All P-sorption curves showed satisfactory agreement with the Langmuir equation. Liming had no effect on q0.2, and reduced qmax only very slightly. Addition of coffee pulp at a rate of 25 g kg-1 reduced q0.2 by 43% whereas a significant decrease in qmax was observed only at the higher rate. Heating the soil at 250 and 500ºC had a tremendous and progressive increase in both q0.2 and qmax. Results of these experiments suggest that in terms of P retention the practice of n’kwop may be detrimental, and that addition of organic materials may be recommended as a means to alleviate the magnitude of P sorption of acid-mineral tropical soils.
