Application of industrial and urban residue and exchangeable of heavy metal on soybean nutrition in no tillage system

Abstract

The rational use of industrial and urban residues in agriculture, under no-tillage system, promotes many benefits on the physical, chemical and biological characteristics of the soil, reducing the use of fertilizers, providing beneficial effects to the ground and the ecosystem. In addition to being attenuators soil acidity, such waste are excellent sources of nutrients; however, depending on the source, you may encounter problems of toxic contamination by heavy metals in soil and plants. However, the efficiency of metal extraction in the soil depends of the used extractor, which always has been using DTPA as standard extractor. However, have been proposed how extractors of heavy metals, in soils treated with residues, the acids organic witch were presents in the vegetable rhizosphere, and they are effective in the dissolution of metals, from sewage sludge, associate to the solid fraction of the soil and whose dissolution kinetics is similar to the absorption of the elements for plants. Thus, considering the successive use of the industrial and urban residues in the soil, with soybean, during eight years, the study aims: a) to find the content of heavy metal (Zn, Pb, Cd, Cr e Ni) in the soil using DTPA and organic vegetable acids; b) to compare the efficiency of the usual extractor of metals in the soil (DTPA) with natural vegetable extractors, the vegetables organic acids (acetic acid, citric acid, lactic acid and oxalic acid), compared to the content of metals in soybean; c) evaluate the foliar nutrients content in flowering as well the nutrients contents in the soybean grain; d) evaluate the residual effect of residue reapplication on content of heavy metal in soil and plant. The experimental delineation used was randomized blocks, with four repetitions. The treatments are composed of four residues, two of urban source, the waste sludge compost (centrifuged and biodigered) and two of industrial source (sludge and steelworks slag of lime), and a control with lime at the recommended dosage to level of adequate pH, the doses of these residues correspond to 0, 0.5, 1 and 2 times the need for setting to achieve optimal pH, equivalent to 0, 2, 4 and 8 t ha-1. Besides the determination of the heavy metals contents in the soil for the extractors, they will be the yield of the soybean and the dry mass of the black oats, cultivated in the rotation system. (AU)