Long-term effects of residual sewage sludge application in tropical soils under Eucalyptus plantations

Abstract

Studies regarding the residual effects of sewage sludge in soil several years after the first and only application are still scarce, especially for tropical areas under forestry management. In these soils, the residual effects can represent a neglected phenomenon, since silvicultural management experiences a longer crop rotation cycle compared to most common agricultural cycles. Consequently, under forestry management, sewage sludge applications can represent an event occurring just once over cycles of several years. This study aimed to evaluate the long-term effects of residual sewage sludge application in infertile tropical soils under Eucalyptus plantations in terms of both the main chemical features (pH, soil organic matter, N, P, S, K, Ca, Mg, and cation-exchange capacity) and the potentially toxic elements (As, Ba, Cd, Co, Cr, Cu, Mo, Ni, Pb, Se, and Zn) concentrations/behaviors of soil. Residual effects were evaluated in four areas (Sao Paulo State, Brazil) after 10.0, 12.2, 12.4, and 17.2 years from the first and only application, respectively. Differences in terms of treatments were evaluated by analysis of variance: correlations and similarity analyzed by principal component and cluster analysis, respectively. The results showed that soil organic matter, main macronutrients (N and P), and cation-exchange capacity contents were generally higher in sewage sludge-treated soils while potentially toxic element contents tended to increase at increasing sewage sludge doses. In most of the investigated treatments, the potentially toxic element concentrations were usually below both the soil natural background concentrations and quality reference values. Principal component and cluster analysis revealed that differences among areas were primary due to differences in applied sewage sludge type and amount. The effects of residual sewage sludge application on soil, in terms of both the pros and cons, can be detected even many years after the first and only application. Studies on the long-term effects of sewage sludge should be mandatory for both monitoring the pedoenvironment and for guiding policymakers and producers on the best practices for their reuse and management. (C) 2019 Elsevier Ltd. All rights reserved.