Physical Fractionation of Organic Matter and Management Impacts of Tropical Soils.

Physical fractionation of organic matter and management impacts of Tropical soils

Moniki Campos Janegitz; Ciro Antonio Rosolem, Gustavo Henrique de Menezes Bacco, Camila Grassmann,

São Paulo State University, College of Agricultural Sciences, C.P.237, Botucatu,

AL 18603-970, Brazil

The increase of soil organic matter (SOM) improves the Cation exchange capacity (CEC) of tropical weathered soils. Moreover, the soil acidity amelioration is required to achieve high yields in these soils. The application of lime may increase SOM with time by improving cation chemical bonds with soil colloids. Soil C fraction may also be affected by different cropping systems. Our objectives were to evaluate the C and soil physical changes under practices as tillage and acidity remediation. The experiment was carried out in an oxisol in Botucatu, São Paulo, Brazil in two fields (no till and conventional systems). The treatments were: control, lime, silicate, gypsum + lime and gypsum + silicate. Limestone, silicate and gypsum rates were calculated to raise soil base saturation to 70%. The initial soil pH was 3.7. The soil samples from both areas were taken one year after treatment applications at depths from 0 to 40 cm, and we examined cation exchange capacity, organic matter and soil porosity. The quantity of total carbon also was analyzed, including carbon particulate and carbon associated minerals (CAM), which were obtained by physical fractionation. The results suggest that C-loss depends on soil management system. The SOM amount caused modification on CEC and carbon physical fractionation. The limestone, silicate and gypsum treatments increased the CEC in soil when compared to control. The silicate used increased labile soil C and C contents in the particulate fraction. Lime + gypsum results in increased soil stable C, and soil physical properties were also influenced in that treatment. 

Acknowledgement: Capes e FAPESP – Proc 2012/09550-0