Fósforo e metais pesados em solos sob cultivo de videiras e sua relação com os atributos microbiológicos do solo

Abstract

The Northeastern region of Brazil accounts for 27% of the national fruit production, especially among vines (Vitis spp.), Whose production management is based on the intensive use of fertilizers and agricultural pesticides. Not only cause losses of production due to nutritional imbalances, but also environmental problems such as contamination of the soil by heavy metals and leaching of phosphorus to water bodies. Thus, the objective of the present work was to evaluate the impacts of the intensive use of phosphate fertilizers and their relationship with microbiological attributes of the soil under vines in the São Francisco Valley. The study areas are located in six grape production farms in the irrigated perimeter Senador Nilo Coelho, Petrolina, PE. In each area, three collection points were randomly chosen, where at each point, rhizospheric (SR) and non-rhizospheric (SNR) soil were removed, which were characterized both physically and chemically. The environmental contents of heavy metals were obtained, aiming to compare them with the Quality Reference Values (VRQ) established for Pernambuco. The dynamics, availability and different forms of P in the soil were evaluated using the sequential method of fractionation and the microbiological attributes: P of the microbial biomass, acid and alkaline phosphatase activity, as well as the glomalin content easily extractable from the soil, were determined according to specific methodologies. The management adopted by grapevine farms resulted in a change in soil fertility in relation to fallow areas, with a significant increase in soil organic matter, Ca, Mg and K levels, besides raising P levels to values higher than critical ground level. The heavy metals contents were similar between the cultivated areas and their respective fallow areas, indicating that these values are obtained from the weathering of the source material and the interaction of these elements and the soil. However, the Cu and Zn contents presented higher values than the VRQ, being this behavior attributed to anthropic interference. Excessive application of phosphate fertilizers contributed to a higher P uptake in soils under vines cultivation. It was observed that, in general, inorganic fractions exceeded the organic fractions of P, with the highest soil P contents found mainly in the fraction not labile, and in the labile fraction. It was observed that the availability of P, where Ca concentration and pH are high, negatively influenced the microbial P contents in the studied areas. The activity of the acid and alkaline phosphatases provided a rapid response to the addition of phosphate fertilizers in the environment, presenting great potential of use in the evaluation of soil quality. In addition, the high concentration of phosphorus in the studied areas significantly influenced the levels of glomalin in the soil. These new indexes can be used to establish a tool for soil quality assessment, contributing to a better evaluation of the impacts of P fertilization on soil microbiological attributes of the semi-arid region of Brazil.