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SOIL CHEMISTRY

Short-Term Reducing Conditions Decrease Soil Aggregation

^a Agronomy Dep., Purdue Univ., West Lafayette, IN 47907
^b USDA-ARS, Grain Marketing and Production Research Center, Wind Erosion Research Unit, 1515 College Ave., Manhattan, KS 66502
^c USDA-ARS, National Soil Erosion Research Lab., 275 S. Russell St., West Lafayette, IN 47907

^* Corresponding author (alfredo_de_campos{at}yahoo.com).

Upland soils in the midwestern United States are often ponded during the spring for days or weeks and may undergo reduction. Short-term reducing conditions change the chemistry of the soil and that may affect soil aggregation. The objective of this study was to determine how changes in the redox status of the soil under a set of controlled temperature and light conditions can impact soil aggregation during short-term flooding conditions. A biogeochemical reactor was built to achieve reducing conditions. Six different soils, three cultivated and three uncultivated, with different organic C contents were incubated (1:1.5 soil/water ratio) in the reactor for 1 h and 1, 3, 7, and 14 d. After each treatment, the soil solution was collected and analyzed for metals and dissolved organic C (DOC). A high-energy moisture characteristic procedure was used to determine the aggregate stability of the incubated soil samples. A strong correlation was found between changes in the redox potential (Eh) and aggregate stability. As Eh decreased, aggregate stability decreased. The changes in redox-sensitive elements (Mn and Fe), alkaline metals (Ca, Mg, and K), and DOC under reducing conditions were found to also contribute to decreased aggregate stability. The aggregate stabilities of cultivated soils were more sensitive to reducing conditions than those of uncultivated ones. The decrease in aggregate stability reached up to 21% in the cultivated soils and might be irreversible under field conditions. Short-term reducing conditions may have detrimental effects on soil structure and water quality due to changes in soil aggregation and the chemistry of the soil solution.

Abbreviations: CEC, cation exchange capacity • DOC, dissolved organic carbon • EC, electrical conductivity • Eh, redox potential • HEMC, high-energy moisture characteristic • SR, stability ratio