Manures used as phosphorus sources may have different efficiencies from those of commercial soluble fertilizers. These efficiencies may vary according to the manure origin and to the proportions of its total P in different chemical fractions. A greenhouse experiment was conducted in order to estimate the efficiencies of dairy cattle and chicken manures as phosphorus source, in comparison to triple superphosphate (TSP), as well as to relate these efficiencies to their P fractions. The treatments were: control, without fertilizer or manure; three rates of P, applied as TSP (6.6, 13.2 and 19.7 mg kg-1 soil); and a single phosphorus application rate of 15.3 mg kg-1 soil, from 11 samples of both cattle and chicken manures. Treatment responses were evaluated cultivating millet during 27 days after P application, in pots filled with a Kandiudult soil. Manure P fractions were determined by sequential extractions. The Efficiency Index (EI), estimated by the TSP equivalence, was 0.84 ± 0.071 for chicken manure, significantly lower than that for cattle manure, 0.94 ± 0.095. There were no statistical differences in EI among manures samples of the same animal species. Considering all samples, EI was positively correlated with proportions of labile P (extracted with resin and NaHCO3) and total inorganic P and negatively correlated with proportions extracted with NaOH and HCl and with total organic P. There was no association between EI and the total P content in the manures.
organic fertilizer; phosphate; efficiency; fractions; waste