Agronomic effectiveness of a granular poultry litter-derived organomineral phosphate fertilizer in tropical soils: Soil phosphorus fractionation and plant responses

Production of organomineral phosphate fertilizers (OMF) from poultry litter (PL) has been suggested to reduce the dependence on phosphorus (P) reserves. Here, we compared a granular PL-derived OMF to triple superphosphate (TSP) in two contrasting tropical soils (Oxisol and Entisol) by using isotope dilution with P-32. Our study aimed to gain insight into soil P fractionation, and P availability to maize plants achieved by P fertilization (0, 25, 50, 75 and 100 mg kg(-1) of soil), in order to investigate the agronomic effectiveness of OMF. Despite mu-XRF maps revealing that the mixture of PL and TSP as OMF resulted in P hot spots disseminated in a low concentration background, whereas for the TSP treatment higher P concentration was uniformly distributed in the granules, there was no difference in maize yield and fertilizer P recovery (%R) between P sources in both soils. In the Oxisol, there was no difference between fertilizers in any of the soil P pools, but larger readily phytoavailable P and smaller moderately labile P fractions were obtained with OMF. In the Entisol, the labile P pool was larger with TSP. Nevertheless, acid and alkaline phosphatase activity and microbial biomass were affected by P rate and P source. The results show that OMF is an effective substitute for conventional phosphate fertilizers, since OMF promotes P recovery, plant P uptake and biomass yields compared to those obtained with TSP.