Long term effect of the sewage sludge on productivity and nutrient cycling in Eucalyptus grandis stands and in cultivation of food plants (simulating change in the agricultural use of the soil)

Abstract

The use of sewage sludge as fertilizer in forestry has been encouraged in several countries, mainly due to the benefits generated by recycling of organic matter and nutrients in the soil. However, the presence of heavy metals in some sewage sludges, as well as the lack of knowledge about long-term effects of sewage sludge use in agricultural environment have led to disposing it into landfills. The hypothesis defended in this research is that sewage sludge applied to the soil, even after many years of its application, continues to have positive effects (residual) on yields and nutrient cycling in eucaliptus stands or in agricultural crops. So, 4 experiments were installed at the Experimental Station of Forest Science, in Itatinga/SP - Brazil (EECFI-ESALQ/USP, by its acronym in Portuguese), in which 3 experiments represent the following forms of eucaliptus management, usually adopted in Brazil: (1st) thinning, (2nd) driving of the regrowth or coppice (in 2nd rotation) and (3rd) reform of the stand. The (4th) experiment simulates a possible change in the agricultural use of soil, shifting from forest plantation to food crop area, considering possible presence and translocation of heavy metals in the soil-plant system. Thus, after many years (1998, 2003 e 2005) since the application of sewage sludge to the soil, in the EECFI, it are being evaluated: eucalyptus growth in managed areas of thinning, coppice and reform of stands; soil fertility variation; production of leaf litter and nutrient cycling in stands of E. grandis. It is also being evaluated the production of biomass and possible assimilation of heavy metals by lettuce, radish e upland rice, grown in soil fertilized by sewage sludge 14 years ago. (AU)