Carbono e nitrogênio nas frações da matéria orgânica de um solo cultivado com cana-de-açúcar na região sudoeste de Mato Grosso

Abstract

Knowing the amount of organic matter in the soil and its compartments is important, as different managements directly influence the availability of nutrients and soil aggregation. The objective of this study was to evaluate the levels of organic carbon and total nitrogen in the compartments of a soil cultivated with sugar cane. The experimental design was completely randomized with five replications, with the cultivation systems being evaluated: native forest (MN), area with vinasse application (CV), without application of vinasse (SV) and area with the harvest of burnt cane (CV) ). In each system, five mini trenches were opened to collect semi-preserved and deformed samples in layers from 0 to 0.05; 0.05 to 0.10 and 0.10 to 0.20 m. With samples with semi-preserved structure, the aggregate classes (2, 1, 0.5 and 0.25 mm) were obtained with dry sizing. The deformed samples were used to physically fractionate the soil sample using the granulometric method, as well as to determine the content of labile organic carbon (CL). Once obtained the aggregate classes and the granulometric fraction, the content of organic carbon (CO) and total nitrogen (NT) was determined. The CO was quantified when digesting the sample by wet combustion in sodium dichromate solution followed by titration with ammoniacal ferrous sulfate. Total nitrogen was determined using the Kjeldahl method. The labile organic carbon (CL) was quantified by means of oxidation with KMnO4. With the COT and CL content data, the Carbon Management Indices (BMI) and lability (IL) were calculated. The data were analyzed through analysis of variance and test of means. The use of vinasse favored a greater increment of TOC and NT in the soil, in particle sizes <53 μm in all layers. The levels of CO and N in the soil aggregate classes were little influenced by management, with the highest levels in the MN and CV systems. The sugarcane cultivation systems, SV and CV, showed higher CL contents, while the CNL content of the MA and CV systems was higher. The carbon management index in all areas cultivated with sugarcane was positive, so that the cultivation of sugar cane regardless of the management adopted did not cause a major impact on the soil.