Micronutrientes e metais pesados no solo e na cana-de-açúcar fertilizada com dejetos orgânicos e adubo mineral

Abstract

Sugarcane culture allows the production of alternative energy sources. Due to increasing mineral fertilizer prices, renewed interest for the rational use of agricultural residues na even urban and industrial ones is observed. Inadequate use of organic residues can add heavy metals to soils and plants. Thus, this study evaluated the movement of micronutrients and heavy metals in the soil and in sugarcane in the region of Uberlândia- MG, after fertilization with chemical fertilizer and organic waste, at different depths and cane growth periods. The study area as the farm of Cia Mineira de Açúcar e Álcool do Triângulo Mineiro Ltda, county of Uberlândia MG. The experimental design was randomized blocks, in a 5x2x4 factorial, with split plots in time, corresponding to five fertilizer types: chicken bedding (CF), turkey bedding (CP), composted manure (AC), cattle manure (EB) and the control, consisting of the mineral fertilizer for the crop, monoamonium phosphate (MAP), all combined with the presence or lack of agricultural gypsum, previously mixed to the fertilizer and applied in the sugarcane planting furrow; analyzed at four depths and at two distinct times of the year, rainy and dry seasons. Soil samples were collected on February and July, at the depths 0-15, 15-30, 30-45 and 45-60 cm, and the concentration of micronutrients and heavy metals was evaluated. Also, these elements were evaluated in sugarcane stalk and leaves. The soil chemical analyses were done as described by Embrapa (1997) while leaf and stalk ones followed Bataglia s (1983). The results obtained were submitted to analysis of variance and the averages of the factors compared by the Tukey test at 0.05 significance. The smallest levels of Cu were observed in time 2 (dry season), opposite to Fe which was in time 1 (rainy season). The high Fe levels in the leaves can be explained by the high Fe contents in the soil. The average Mn value in the leaves is 159 mg kg-1 and is within the adequate range for the crop. The leaf contents of Ni, Cd and Cr did not present differences between the sampling times for all treatments. The micronutrient contents and those of heavy metals in the stalks were smaller in time 2. Micronutrient leaf contents were below the adequate range for sugarcane, except for Fe. In contrast, micronutrient stalk contents were in the ideal range for the crop, while the heavy metals did not exceed the critical limit. The micronutrient concentrations in the soil were below the adequate range, except for Zn. No Cd and Cr were detected in the soil, while Ni and Pb were below the critical contamination limit. Agricultural gypsum did not affect the levels of micronutrients or heavy metals in the soil or in the sugarcane.