Revista Brasileira de Ciência do Solo (Oct 2007)
Substâncias húmicas, atividade microbiana e carbono orgânico lábil em agregados de um Latossolo Vermelho distrófico sob duas coberturas vegetais Humic substances, microbial activity and labile organic carbon in aggregates of a Dystrophic Red Latosol under two vegetation covers
Abstract
A matéria orgânica (MO) constitui um atributo indicativo da qualidade do solo. O conhecimento de seus distintos componentes, explicando a influência que as práticas de manejo exercem sobre a MO e a agregação dos solos, é de grande importância para a sustentabilidade dos sistemas agrícolas. Neste trabalho, avaliaram-se as substâncias húmicas, a atividade microbiana e o C orgânico lábil em agregados de um Latossolo Vermelho distrófico de Minas Gerais sob vegetação natural de Cerradão e sob cultivo convencional com milho durante 30 anos. Para isso, foram retiradas amostras de solo nas profundidades de 5-10 e 15-20 cm em quatro pontos diferentes. Após coletado, o material foi seco ao ar e fracionado, por via seca, nas classes de agregados de: 4,75-2,0; 2,0-1,0; 1,0-0,5; 0,5-0,25; 0,25-0,105; e Organic matter is an indicator of the soil quality. Knowledge about its different components, explaining the influence of management practices on organic matter and soil aggregation, is essential for the sustainability of agricultural systems. In the present work, we evaluated humic substances, microbial activity and labile organic carbon in a Dystrophic Red Latosol from Minas Gerais state, Brazil, under natural vegetation (Cerradão) or under 30-years of conventional corn cultivation. Soil samples were collected from depths of 5-10 and 15-20 cm at four different sites. Then the samples were dried and fractioned in aggregate classes (diameter 4.75-2.0; 2.0-1.0; 1.0-0.5; 0.5-0.25; 0.25-0.105; and less than 0.105 mm). Furthermore, organic carbon of fulvic acid (AF), humic acids (AH) and humins (HUM) fractions, and labile organic carbon (COL) using KMnO4 15.6 and 33.0 mmol L-1 of the samples were determined. The material was further subjected to a respirometry test, in which CO2 production values were adjusted to logistic equations [Y = a/1 + e-(b + cx)] to estimate the time needed to achieve half of the maximum CO2 (t1/2), production. Results showed higher mean organic carbon contents in the AH fraction and COL with KMnO4 33.0 mmol L-1 of soil aggregates under conventional tillage. For AF and HUM fractions and COL with KMnO4 15.6 mmol L-1 this behavior was only observed in the 15-20 cm layer. The highest CO2 production was observed in the aggregates of the soil under Cerradão. The smaller aggregates tended to present higher organic carbon contents in the AF and AH fractions and COL. These were responsible for the highest CO2 production and constituted favorable sites of organic matter storage, due to the physical and chemical protection, as well as for mineralization, since microorganisms prefer these sites. The coefficients of the logistic equation (a, b, c) and the t1/2 can be considered important indicators of organic matter quality and lability under different managements.
Keywords
