Lodo de tratamento de água eutrofizada como fonte de fósforo para a agricultura

Abstract

Phosphorus (P) is an important element that contributes to eutrophication, and its removal is considered an efficient way of treating eutrophic waters. In the chemical removal the aluminum present in modified clays remove phosphorus by adsorption. At the end of the chemical removal process we have the production of a significant amount of P-rich sludge, which has no predetermined destination. It was hypothesized that increasing doses of this sludge, applied in soil with pH higher than 5.5, increase the availability of P and contribute with the plant development differently of the application in soil with pH bellow 5. In this study, the objective was to test a sludge from the treatment of eutrophic water as a phosphate fertilizer, evaluating it for its doses in two types of soil (pH below 5.5 and pH above 5.5), grown with maize. In February 2019 was conducted two experiments in greenhouse, both with a completely randomized design (DIC) with 5 treatments (sludge 0, 15, 30, 60 and 120 Mg ha-1 equivalent to 0, 30, 60, 120 and 240 kg ha-1 of P2O5) and 4 repetitions. The experimental units were vessels filled with the soils that received the doses of the sludge on wich was sown the corn. At 30 days after the sowing, was performed measures of height and diameter, shoot and root biomass, content and accumulation of macro and micronutrients in the shoots. In the soil were evaluated the chemical attributes for fertility purposes. With the verification of the data normal distribution, was carried out the analyses of variance and the analyses of regression with line adjustment. In the soil with pH over 5,5, the doses of sludge improved the P contents (5.5 mg kg-1 to 8.7 mg kg-1), of Na (from 0.25 to 0,56 cmolc kg-1) and reduced the pH (from 6.6 to 6.1). In the same soil the doses of sludge afford bigger leaf area (284.66 cm²) and bigger P content in plants (2.61 g kg-1). In the soil with pH above 5.5, there was an increase in P availability (from 0.21 to 0.48 mg kg-1) and Al content (from 0.5 cmolc kg-1 to 0.7 cmolc kg-1), without relevant changes in plants. The 60 Mg ha-1 sludge dose, corresponding to 120 kg ha-1 of P2O5, in soil with pH above 5.5 favors the supply of P to maize crop, being necessary to pay attention to Na+ levels in the soil.