Economic feasibility of the application of sewage sludge in eucalyptus plantation

Abstract

Sewage sludge (LE) applied to planted forests soils, based on the nitrogen criterion, can increase wood production without damaging the forest environment. However, it is still necessary to analyze the economic viability of this practice, which may be a limiting factor for the recycling of this residue. The objective of this work was to evaluate the use of LE (0, 7.7, 15.4 and 23.1 Mg ha^-1) without and complementation of nitrogen and phosphatic fertilizer compared to conventional fertilization of Eucalyptus grandis plantation at 7.9 years after planting by means of the Annual Net Present Value (VPLA), Internal Rate of Return (TIR) and Benefit/Cost Ratio (IBC). Discount rates of 6 and 12% per year and three scenarios were considered in which the forest producer assumes 100, 50 and 0% of the costs of transporting the sludge. It was verified a higher wood production in the treatment with 15.4 Mg ha^-1 of LE, which obtained 338 m³ ha^-1. Althought, conventional mineral fertilization represented the option with better economic viability in all situations analyzed, except for the scenario in which the forest producer would be exempt from LE transportation. It was noted that the variation in the proposed interest rates provided higher increases in VPLA than the change in scenarios (reduction of transport costs). Therefore, it is concluded that this forest producer would only be motivated to apply the sewage sludge in relation to the usual practice if the cost of transportation of this waste was not afforded by he. It is important to also consider that the risk factor associated with the LE market for agricultural application, which is not structured and coordinated, may interfere in this producer's decision-making.