Saturday, 15 July 2006

Influence of REDOX on the Rhizosphere Chemistry of Upland Soils.

A.B. De–Campos1, C.T. Johnston1, C. Huang2, and L.D. Norton2. (1) Agronomy Dept, Purdue Univ, 275 S. Russell Street, West Lafayette, IN 47907, (2) USDA-ARS, 275 S. Russell St., Purdue Univ, West Lafayette, IN 47907-2077

Many upland soils in the Midwest of the US are temporally flooded during the Spring. These soils can remain water saturated for days, weeks, or even months. The effects of prolonged saturation on the biogeochemical processes that occur in these soils are not fully understood and are the subject of this study. To evaluate the biogeochemical changes that occur in these soils during prolonged saturation, we investigated the REDOX-induced changes in the soil solution with an emphasis on N, P, and REDOX sensitive constituents. Soil solution chemistry was investigated for a silty clay loam soil (Udollic Epiaqualfs) that was saturated for 1 hour, 1, 7 and 28 days. In addition, CO2 evolution from these soils was measured as a measure of the biological activity for these four hydrologic treatments. Samples were analyzed for pH, REDOX potential, P, NO3-, NH4+, and REDOX-sensitive constituents Fe, Mn, S, and dissolved organic carbon. REDOX induced changes included: a lowering of the REDOX potential after 7 days, an increase in pH of up to 2.3 units after 28 days, a decrease in NO3- and an increase in NH4+, total P, Fe, Mn, DOC. The net CO2 evolution over the 28 days was 14 umol/g. The changes in REDOX are strongly coupled with changes in pH, and the chemical composition of the soil solution. These results have important implications for potential impact on offsite water quality.

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