Soil organic carbon in no-tillage systems of different ages in Southwest Mato Grosso, Brazil/Carbono em solos sob plantio direto de diferentes idades no sudoeste de Mato Grosso, Brasil

The objectives of this study were to evaluate the effect of the no-tillage system on soil bulk density, soil organic carbon, and carbon stocks in Plinthic subgroups and Oxisols, located in Pontes and Lacerda, State of Mato Grosso, Brazil. The treatments were native vegetation and no-tillage systems established for 3, 8, 10, and 12 years. To analyse soil organic carbon, soils were sampled in each area, with three repetitions, at layers of 0-0.05; 0.05-0.10; 0.10-0.20; 0.20-0.40; 0.40-0.60; 0.60-1.00; 1.00-1.50 and 1.50-2.00 m. For soil bulk density, undisturbed samples were collected at layers of 0-0.20 and 0.20-0.40 m. Compared with areas of native vegetation, soil bulk density values after 12 years increased by 25% in Oxisols and 30% in the Plinthic subgroups. In Oxisols and Plinthic subgroups, respectively, organic carbon concentration was, on average, 20.57, 25.04 g [kg.sup.-1] under native vegetation; 16.82, 16.59 g [kg.sup.-1] after 3 years of no-tillage; 13.31, 4.96 g [kg.sup.-1] after 8 years; 16.52, 14.39 g [kg.sup.-1] after 10 years; and 17.97, 18.53 g [kg.sup.-1] after 12 years. In both soils, the no-tillage system contributed to an increase in carbon stocks over the years, but not at depth, being generally limited to the top 0.20 m of the soils. Compared to native vegetation, after 12 years of no-tillage, carbon stocks decreased at a rate of 0.075 Mg [ha.sup.-1] [year.sup.-1] in the Plinthic subgroups and increased by 2.3 Mg [ha.sup.-1] [year.sup.-1] in Oxisols. Key words: conservationist agriculture, soil carbon stocks, bulk density, Oxisols, Plinthic subgroups Objetivou-se neste estudo avaliar o efeito do plantio direto sobre a densidade do solo, o teor de carbono organico do solo e o estoque de carbono em Plintossolo Petrico e Latossolo Vermelho-Amarelo (Oxisols), localizados no municipio de Pontes e Lacerda, no Estado de Mato Grosso, Brasil. Os tratamentos foram vegetacao nativa e plantio direto de 3, 8, 10 e 12 anos. Para as analises de carbono organico do solo amostras de solo foram coletadas em cada area, com tres repeticoes, nas camadas de 0-0,05; 0,05-0,10; 0,10-0,20; 0,20-0,40; 0,40-0,60; 0,60-1,00; 1,00-1,50 e 1,50-2,00 m. Para a densidade do solo foram coletadas amostras indeformadas em 0-0,20 e 0,20-0,40 m. Comparando-se com a vegetacao nativa, os valores da densidade do solo aos 12 anos aumentaram 25% no Latossolo Vermelho-Amarelo e 30% no Plintossolo. No Latossolo e Plintossolo, respectivamente, os teores de carbono organico foram