ARS | Publication request: Biogeochemistry of Terrestrial Soils as Influenced by Short-term Flooding

Submitted to: Biogeochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 1, 2011
Publication Date: N/A

Interpretive Summary: Many farm fields in the US Midwest are sometimes flooded during the spring. Flooding causes the depletion of oxygen and triggers reducing condition. How a soil would respond to a reducing condition under long-term flooding has been studied extensively for wetlands. It is not clear the extent of biogeochemical processes occurring during one to two weeks flooding on upland soils. We designed a reaction chamber to capture the evolved CO2 and measure the solution chemistry for 3 cultivated and 3 uncultivated soils subjected to flooding for a 14-day period. We found, for uncultivated soils, a quicker establishment of the reducing condition, a greater increase in solution pH, and greater amounts of manganese, iron, ammonium, phosphorus, and carbon, as compared to those measured from the cultivated soils. The released carbon is the sum of evolved CO2 gas and dissolved organic and inorganic carbon in solution. The uncultivated soils released about 900 µg of carbon per gram of soil compared 240 µg of carbon for the cultivated soils, indicating an inherent difference in the types of carbon in these soils with more reactive carbon components in uncultivated soils. Our results showed that farming practices and soil management can affect soil chemical and biological properties and impact the soil solution chemistry and release of carbon during a short term flooding. We anticipate this research to be useful to the scientific community in understanding basic processes occurring in upland soil during the time of flooding.

Technical Abstract: Many upland soils in the US Midwest are temporally flooded during the spring. The effects of short-term flooding on the biogeochemical processes that occur in these soils are not fully understood and are the subject of this study. To evaluate these biogeochemical processes, we investigated the REDOX-induced changes in the soil solution for three cultivated and three uncultivated/forest soils with different organic matter contents. The test soils were flooded for 1, 3, 7, and 14 days under anaerobic conditions in a biogeochemical reactor. Samples were analyzed for Eh, pH, NH4, REDOX-sensitive constituents NO3, Mn, and Fe, dissolved organic and inorganic carbon (DOC and DIC), and P. In addition, CO2 evolution from these soils was measured as a measure of the biological activity. We found different responses of upland cultivated and uncultivated soils to flooding. The reducing condition was established very quickly in the uncultivated soils (Eh values of ~ -100mV within one day of incubation) and more slowly in the cultivated soils. Changes in pH were higher for the uncultivated soils. The uncultivated soils showed a greater increase in NH4, P, Fe, and Mn than the cultivated soils over the incubation period. Release of carbon was much greater for the uncultivated soils with approximately 900 µg of carbon released per gram of soil compared 240 µg of carbon for the cultivated soils, indicating differences in the type of carbon. The rapid onset of reducing conditions for the uncultivated soils can be attributed to a reactive carbon component that is either absent or occluded in the cultivated soils. This shows soil management can affect the solution chemistry and the release of carbon in upland soils under short-term flooding.