Comportamento do carbono e nitrogênio em gleissolos sob diferentes usos da terra no sul de Minas Gerais

Abstract

Soil organic carbon (SOC) is an important indicator of soil quality, and a nutrient source for plants and soil organisms. Thus, it is critical to develop sustainable agricultural practices favoring SOC conservation or sequestration, such as minimal tillage, crop rotations and judicious fertilizer use. In lowlands, seasonal or permanent anoxia due to flooding changes microbial communities, which become less efficient in decomposing SOC, causing its accumulation. This research aimed to study land use effects on SOC in a gley soil in southern Minas Gerais, Brazil. Treatments comprised a gley soil under native forest vegetation, common beans and flooded rice, as well as a nearby Ultisol under native forest as a reference of aerated soils. Soil samples were taken at the 0-5 cm, 5-10, 10-20 and 20-40 cm depths for physical, chemical, SOC and N analyses. The experimental design was completely randomized, with 4 treatments in triplicate. Liming and fertilization increased soil pH and base saturation, and decreased aluminum saturation in cultivated gleys. Higher concentrations and stocks of SOC and N occurred in the gley soil under native vegetation than under rice and bean crops. The Ultisol and the gley soil under native vegetation did not differ in SOC stocks, since the latter showed simultaneously higher SOC concentrations but lower bulk density. This trend suggests that flooding and anoxia had lower importance for SOC and N retention than previously expected, in the study area.