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

Over the last few decades, the increase in consumption and in the cost of mineral fertilizers has concerned overall agriculture. Therefore, the use of treated sewage sludge (biosolids) as fertilizer has being encouraged in many countries, inasmuch as it increases productivity and generates benefits by the recycling of organic matter and nutrients in its composition. Nevertheless, the presence of potentially toxic elements (e.g. heavy metals) in the sludge and the lack of knowledge about its long term effect on the environment, especially in cases where there is a change in agricultural use, have contributed to its final disposal in landfills. This research assumes that the agricultural use of sewage sludge, even some time after its application to the soil, have a favorable long term effect on productivity (biomass) and nutrient cycling in eucalypt stands, as well as in cultures of food plants. For this study, three experiments with Eucalyptus grandis were installed in Itatinga/SP: (1) Thinning practice in two eucalyptus stands planted in 1998, on sandy and clayey ferralsol (LVA and LVE, by its acronym in Portuguese), both fertilized with 20 t ha-1 of sewage sludge; (2) Coppicing practice (sprouting conduct) in eucalyptus plots fertilized (in 2003) with 10, 20 and 30 t ha-1 of wet and dry sewage sludge; and (3) Reform techniques in eucalyptus plots fertilized (in 2005) with 15 t ha-1 of sludge produced by Barueri\'s, São Miguel\'s and Parque Novo Mundo\'s wastewater treatment plants. A fourth experiment simulated the change of use of agricultural soil, by replacing eucalyptus stands fertilized with sewage sludge (fourteen years ago) for vegetable species: Lactuca sativa L. (lettuce), Raphanus sativus L. (radish) and Oryza sativa L. (upland rice). In this experiment, plants were grown in pots filled with two types of ferralsol (LVA and LVE), both collected in E. grandis stands fertilized with sewage sludge (14 years ago). In general, the eucalyptus stands fertilization with sewage sludge increased the phosphorus, calcium and zinc content in the soil. In thinning stands, the leaf nutrient concentrations were greater in trees grown under long term effect of sewage sludge; however, this effect was not sufficient to alter the growth of the trunk (in circumference). In coppice stands, the fertilization with 10 t ha-1 of dry sewage sludge had positive long term effect on the biomass production. In areas undergoing stand reform, the biomass accumulated by trees grown on long term effect of the sewage sludge was greater (150%) than the control. Furthermore, this effect of the sludge also brought positive impacts on nutrient cycling, due to an increasing in the leaf fall production. Under the long term effect of sewage sludge, the food plants accumulated 2 to 5 times more biomass than respective control treatments, especially if they are grown on the LVA. These plants also showed greater cadmium concentrations in the leaves, as well as greater chromium and nickel concentration in the roots. However, the concentrations of heavy metals didn\'t exceed the limits recommended by the Brazilian Health Surveillance Agency (ANVISA, by its acronym in Portuguese) in any of the crops. (AU)