Produtividade, fertilidade e fauna do solo em um Argissolo Amarelo cultivado com cana-de-açúcar sob diferentes sistemas de colheita

Abstract

The study was conducted in an area of Usina LASA, in Linhares municipality, Espírito Santo State, located in the Baixo Rio Doce stratigraphic zone, in a sandy loam Xanthic Ultisol. The remaining primary vegetation is represented by the Tropical Rainforest and the local altitude is of 28m. The climate is Aw in the Köppen classification. Sugar cane is highly important economically and it has a favorable production scenario in Brazil - world's largest producer and holder of technology for producing ethanol from sugar cane. However, the pressures for inclusion and/or expansion of renewable sources in the global energy matrix, toward the mitigation of greenhouse gases, and the ban on burning practices in the management of sugar cane, made necessary to evaluate the effect of maintenance or disposal of cane stubbles on the soil surface. Thus, the objectives of this study were: to consolidate information on a long term experiment in the studied area, about soil fertility and fauna (Chapter I); to assess the impact promoted by harvesting management on soil fertility parameters (Chapter II), on soil macrofauna activity (Chapter III), and on crop productivity (Chapter IV). In Chapter I, the compilation of studies showed that stubble positively influences, on soil surface, the values of organic carbon, pH, Mg, Ca, S value, V value, and CTC (T value); the cane burning, adding ash, increased K and P levels on surface, and Ca and Mg in depth. Regarding soil fauna, cane treatment without burning showed superiority of earthworm population in two seasons, and soil mesofauna at 0-5 cm depth; otherwise the treatment with cane burning allowed for a greater number of individuals in the 5 - 10 cm layer. In both treatments, the same functional groups were observed, but for burnt sugar cane, the presence of microphagous, which live at a lower soil depth and take advantage of the organic matter supplied by the root system, was greater. The green cane showed greatest presence of larvae (saprophages). In the Chapter II, the results indicated that treatment with stubble maintenance showed, on the surface, highest values of organic carbon, H + Al, Ca, Mg, S and T values. The burnt treatments showed the highest values of K and P on surface, reflecting the composition of the ash material where it was originated (cane straw). Among the sampling periods, there were differences due to climate conditions, which contributed for organic carbon decomposition in the soil. In the Chapter III it was concluded that the indexes of Shannon diversity and richness were more efficient than the total density to evaluate the influence of cane harvesting systems, with the highest values related to areas harvested without burning. In the Chapter IV, the effect of the treatments on stems and leaves yield was not detected; however it was noted in the evaluation of pointers, where the highest productivity occurred in the green cane system.