Soil chemical and physical attributes in areas of Eastern Amazon conversion in pasture and no-tillage

Abstract

For the understanding and development of sustainable agricultural systems, it is important to evaluate the impacts on the physical and chemical properties of the soil from the conversion of natural areas to agriculture and pasture. The objective was to evaluate the quality of an Oxisol, silty clay loam texture, in native forest (MAT), pasture, (PST) and no-tillage (CTV) in the municipality of Paragominas, PA. The soil samplings were performed in a period of high and low precipitation. The soils chemical attributes were evaluated in the layer of 0 to 0.20 m, and the physicals (soil bulk density (BD), soil penetration resistance (PR), total porosity, micro and macroporosity (Ma)) were determined for the layer of 0 to 0.10 m. The means (when significant) were compared by the Tukey test (p <0.05). Multivariate analyzes were also performed to verify the similarities between the three soil uses (Cluster analysis) and description of the soil attributes that most contributed to the variance among the clusters (canonical redundancy analysis). Soil uses and precipitation were factors of differentiation between physical-chemical attributes, indicating similarities between MAT and PST. The conversion of MAT to PST resulted in a decrease in soil quality. The soil management used in CTV modified soil characteristics without loss of chemical quality, but the physical attributes are not favorable for plant growth (high BD and PR and low Ma). The best indicators for the evaluation of land use change in the studied region were: PR, Mg^{2 +}, H + Al, BD and CEC.