Micromorphology and Organic Carbon Studies on Water Stable Aggregates from Savanna Soils of Central Brazil. (5224)
Authors:
Y. Zinn* - Ohio St. University R. Lal* - Ohio St. University
D.V.S. Resck - Embrapa Cerrados, Brazil
Abstract:
Sesquioxides, organic C and soil fauna play an important role in the aggregation of tropical soils, but little quantitative information exists. Four different soils (90 to 700 g clay/kg soil) from the Brazilian Cerrados were sampled in triplicate, wet-sieved (Yoder technique) and analyzed for soil organic carbon (SOC) content. Water-stable aggregates (WSA) 2-8mm from 0-5, 30-40 and 90-100 cm depths were analysed for SOC and micromorphology. In all soils and depths, WSA 2-8 mm are mostly subangular blocks. In the 0-5 cm depth, WSA 2-8mm had lower SOC than bulk soil, because of free particulate organic matter (POM) in topsoil, whereas WSA 2-8 mm were SOC-richer in the lower depths, esp. in coarser soils. SOC in WSA 2-8 mm is mostly colloidal: thin sections contained little POM. In thin sections, the Oxisols have a porphyric, and sandy soils a dermatic or intertextic, c/f distribution. All have an asepic or isotropic s-matrix. With WSA size distribution in depth, this indicates a major role of colloidal SOC and clay/sesquioxides in aggregation. Significant part of WSA 2-8 mm in the 0-5 cm depth has faunal origin, subdivided into a) aggrotubules, b) fecal pellets and c) cocoons. Aggrotubules are the most common, varying from 6 to 27% of total WSA 2-8mm mass in the sandy and clayey soils, respectively. Aggrotubules of coarser soils had much higher SOC than bulk soil and WSA 2-8 mm.
Speaker Information: Yuri Zinn, Ohio St. University, 1170 Chambers rd apt. 1B, Columbus, OH 43212;
Phone: 614 481 8112; E-mail: [email protected]
Session Information: Tuesday, November 2, 2004, 3:00 PM-5:00 PM Presentation Start: 3:00 PM (Poster Board Number: 1938) Keywords: Brazil; Savanna; Aggregation; Soil Organic C