Soil organic carbon variations due to deforestation and natural regeneration

A flutua\ue7\ue3o no conte\ufado de mat\ue9ria org\ue2nica do solo \ue9 severamente afetada pelo uso e manejo do solo. Em solos f\uedsica e quimicamente fr\ue1geis a destrui\ue7\ue3o da vegeta\ue7\ue3o nativa pode levar a diminui\ue7\ue3o dr\ue1stica do estoque de carbono. No entanto, solos jovens que apresentam alta resili\ueancia, quando manejados adequadamente, podem recuperar facilmente os valores originais de carbono. O objetivo deste trabalho foi quantificar os teores de carbono org\ue2nico de um Neossolo e um Chernossolo em decorr\ueancia de seu uso, em especial ap\uf3s o desmatamento e revegeta\ue7\ue3o natural. Coletaram-se amostras de duas camadas (0-5 e 5-15 cm) em dois solos (Neossolo e Chernossolo) ocorrentes numa pequena bacia hidrogr\ue1fica com relevo fortemente ondulado, com quatro condi\ue7\uf5es de uso (mata nativa, lavoura nova, lavoura velha e revegeta\ue7\ue3o com capoeira). Avaliaram-se a distribui\ue7\ue3o granulom\ue9trica, a densidade do solo e os teores de carbono org\ue2nico. Os dados foram submetidos \ue0 an\ue1lise estat\uedstica considerando um delineamento inteiramente casualizado, num esquema trifatorial (tipos de solos, tipos de usos e camadas amostradas). O estoque de carbono do solo diminuiu ap\uf3s o desmatamento para a inastala\ue7\ue3o de culturas anuais com baixa adi\ue7\ue3o de res\uedduos e revolvimento intenso do solo. A revegeta\ue7\ue3o natural das \ue1reas degradadas pelo cultivo convencional recuperou rapidamente o estoque de carbono dos solos, mesmo permanecendo as impress\uf5es herdadas da eros\ue3o (menor teor de argila) e da aplica\ue7\ue3o de fertilizantes e corretivos (menor acidez potencial e maior disponibilidade de f\uf3sforo e pot\ue1ssio).The soil organic matter content is severely affected by soil use and management. In physically and chemically fragile soils the destruction of native vegetation can cause a great decrease in the carbon stock. However, soils that present high resilience, when appropriately handled, can easily recover the original values of carbon. The objective of this research was to quantify and analyze organic carbon of young soils in relation to their use, especially those in natural regeneration. Samples of two layers were collected (0-5 and 5-15 cm) in two soils (Neossolo and Chernossolo) that occur in a headslope watershed, with four use conditions (forest, new farming, old farming and regeneration). Particle size distribution, soil bulk density and organic carbon were evaluated. The data were submitted to statistical analysis considering a completely randomized design, in tri-factorial outline (soil types, uses and sampled layers). The soil carbon stock decreased with deforestation for annual plantation of crops with little addition of residues and intensive soil turbation. The natural regeneration of degraded soils by conventional tillage recovered the soil carbon stock quickly, even when there remained impressions from erosion (lower clay) and from the application of fertilizers and correctives (lower potential acidity and larger phosphorus and potassium availability)