Matéria orgânica e qualidade estrutural de um Latossolo sob cultivo de cana-de-açúcar no Rio Grande do Sul, 2013

Abstract

According the increase in demand for renewable energy to replace those fossil, the sugarcane crop has assumed importance in the nationally and internationally energy matrix. However, because the heavy soil preparation for the implantation of culture and harvest by previous burning of stubble have been observed negative impacts on the chemical and physical quality of soils cultivated with sugarcane. This study is structured in two articles, the first is to evaluate the aggregation, the physical fractions of organic matter (OM) and carbon management index (CMI) of an Oxisol cultivated with sugarcane in the Rio Grande do Sul state (RS), and the second article was to evaluate the tensile strength (TS) and friability (F) of an Oxisol cultivated with sugarcane in RS state. The experimental design was completely randomized and the treatments consist of various cycles of sugarcane: plant sugarcane (CP), second ratoon sugarcane (C2), fourth ratoon sugarcane (C4). As a reference we used an area of native forest (NF) with characteristics and properties of soil and topography similar by the others. In each area were collected undisturbed and disturbed samples in layers from 0.00 to 0.05, from 0.05 to 0.10 m and from 0.10 to 0.20 m to quantify the percentage of water stable aggregates (WSA), the mean weight diameter (MWD), total organic carbon (TOC), carbon from the coarse fraction (CCF), the carbon associated with minerals (CAM), carbon free light fraction (FLL), carbon occluded light fraction (OLF), carbon from the heavy fraction (HF), CMI, TS and F.The soil preparation for the deployment of sugarcane, combined with previous burning of stubble contributed to the reduction of young carbon cycling in the soil, reflecting negatively on the stocks of physical particle size fractions of the OM and on distribution and aggregate stability, except for the HF. With the exception of NF in the surface layer, the proportions of physical density fractions of OM in relation to TOC increased in order FLF<OLF<HF. All areas cultivated with sugarcane present CMI lower than 100, with the lowest values observed in C2, indicating negative impacts on stocks of OM and on soil quality. In the surface layer, the TS increased in depth and proportionally with the reduction of the levels of TOC. In the surface layer, the soil was classified as very friable and in the other layers, the areas C4 and MN presented themselves as friable. The TS and the F were sensitive to detect differences in the structural quality of the areas cultivated with sugarcane.