S. T. Spera

Dispersão de argila em microagregados de solo incubado com calcário

Soil compaction limits grain yields. Among others factors, soil amendment with agricultural lime can contribute to micro-aggregate dispersion and the formation of compacted layers. The objective of this study was to evaluate the effect of lime on soil physical attributes related to soil compaction. The experiment was carried out in PVC columns, in a glass house, during 18 months. Sterilized and non-sterilized samples of a dystrophic Red Latosol (Hapludox) were incubated with 0, 1.9, 3.8, 5.7, 7.6 and 15.2 Mg ha-1. After the incubation period, the micro and macro porosity, soil density, clay dispersion, hydraulic conductivity and concentration of exchangeable Al, Ca and Mg and soil organic matter were evaluated. Soil density, clay dispersion, pH and Ca and Mg concentration increased with lime application, while macro porosity, hydraulic conductivity, soil organic matter, and Al decreased. The increase of pH and hydraulic conductivity were higher in the sterilized soil. Liming effects were more evident at a rate of 3.8 Mg ha-1. Soil sterilization increased the pH value and decreased the organic matter content and Ca, besides the hydraulic conductivity. Micro- aggregate dispersion in limed soils can, at least partially, contribute to soil compaction.

Atributos químicos e físicos de solo sob pastagens perenes de verão

Soil chemical and physical characteristics were evaluated on a Rhodic Nitisol Eutrophic clayey located in Passo Fundo, Rio Grande do Sul State, Brazil in a trial of agronomic performance of three perennial summer grasses (kikuyu grass, elephant grass and Tifton 68 grass) for milk production after two growing seasons. The trial used a complete randomized block design replicated three times. Soil samples were also taken in a fragment of subtropical forest near the experiment. Soil reaction (pH), aluminum, calcium, magnesium, and phosphorus varied according to the studied soil layer. Some grasses increased the level of phosphorus content in all layers. Pastures increased accumulated carbon levels in the 0-20 cm layer in comparison to subtropical forest. No differences among grass species were observed for soil organic matter contents. Soil bulk density and soil mechanical resistance did not differ among pastures in both sampling layers. However, in the 0-5 cm layer (and in the 10-15 cm), these values increased in comparison to the subtropical forest. Total porosity and macroporosity did not differ among of three grass species, but the values were respectively lower and greater in comparison to soil forest.