Plant-availability and fate of P from applied phosphatic fertilizers in two latosols

The effectiveness of fluid (phosphoric acid, H3PO4 and 10-30-00 colloidal suspension, CS) and solid (monoammonium phosphate, MAP and triple superphosphate, TSP) fertilizers and the fate of fertilizer P to inorganic P fractions were evaluated in laboratory and in a greenhouse experiment. Corn plants were grown in pots (8 plants per pot; 3 replicates) containing 1 kg of two red-yellow Latosols with different phosphorus retention capacities, for three successive cycles (30 days each). The fertilizers were applied prior to the first sowing at rates of 0 (control), 70, 140 and 210 mg P2O5 kg-1 (0, 30.6, 61.2 and 91.8 mg P kg-1). Dry matter yield and total P were determined at each harvest time. Results showed no difference between the effects of fluid and solid phosphate fertilizers on dry matter yield and phosphorus uptake. However, the rates of phosphorus applied were significantly and positively related with dry matter yield and phosphorus uptake. In both soils, the agronomic effectiveness of fluid and solid phosphate fertilizers was equivalent. A laboratory experiment was carried out to measure the fate of P fertilizers converting into inorganic soil P fractions after incubation over a period of 30 days in both Latosols. Inorganic soil phosphates were fractionated and P derived from fertilizer was determined in each fraction. The larger parts of soil applied phosphates were recovered as aluminum (PAl) and iron bound P (PFe) fractions. Only small quantities of fertilizer P were found as water soluble P, calcium bound P and occluded P. The P derived from H3PO4, MAP and CS was retained in more stable forms than that derived from TSP. The proportion of PAl to PFe was larger in soil B, which had less P fixing capacity, than in soil A. This result suggests that PAl fractions were more available to plants than PF-e. (author)