Technologies for the efficient use of phosphorus in the plantsoil-fertilizer system

Abstract

Phosphorus (P) is a nutrient that naturally limits plant growth in most Brazilian soils. This condition requires a continuous application of phosphate fertilizer to sustain a satisfactory production of crops and to provide food to a growing population. However, conversion of P applied to soil in products of human needs is very low, which requires the adoption of strategies of management and development of fertilizers more effective in increasing the recovery efficiency of P-fertilizer by plants. Thus, application of humic acid (HA) in soil as well as formulations of organo-mineral fertilizers (OMFs) and, magnesium phosphate compounds (MPCs) were studied. The aims of this thesis were: (i) to evaluate adsorption and availability of P in soils limed with CaCO3 or MgCO3 combined with HA rates; (ii) to investigate organic matter decomposition, N loss and soluble P fractions in mixtures of chicken manure (CM) and coffee husk (CH) with monoammonium phosphate (MAP) or phosphate rocks (PRs) submitted to composting for OMFs production; (iii) to synthesize MPCs, to characterize P contents, and to verify agronomic performance of MPCs using maize as the test plant. Initially, Oxisol and Entisol samples were incubated with HA rates combined with CaCO3 or MgCO3, as liming materials, and subsequent evaluation of P adsorption. In sequence, these soil samples were again incubated with P source, to evaluate P availability. After incubations, it was verified that HA reduced buffering P capacity and increased P availability in Oxisol, whereas, application of HA in Entisol did not alter these response variables. For OMFs formulations, mixtures of PRs, after 150 days of composting, presented greater decomposition of organic wastes, CM and CH, in comparison to MAP-based composts. MAP use in composting resulted in greater dry mass yield and N retention in final composts when compared to PRs-mixtures. Composting of CM and CH with PRs did not alter the soluble P fractions and it was not an efficient process to produce OMFs. In contrast, composting of CM, CH and MAP reduced water-soluble P and increased the value as fertilizer of the produced composts. Finally, six different mixtures of P and Mg generated MPCs, which presented partially water-soluble P and totally soluble in neutral ammonium citrate plus water. Synthesis process of MPCs transferred to P a slower release than P from triple superphosphate (TSP). Maize fertilization with one of formulated MPCs resulted in a greater dry mass production in relation to application of TSP and higher P accumulation in maize shoot, compared to the others MPCs tested.