Tuesday, November 14, 2006

Effects of Organic Matter on New Redoximorphic Feature Formation Under Induced Hydric Soil Conditions.

Adam Gray and Martin C. Rabenhorst. Univ of Maryland, 1112 HJ Patterson Hall, College Park, MD 20742

Organic matter provides a critical energy source for soil microorganisms that is necessary for the reduction of iron during the development of redoximorphic (hydromorphic) features in soils with impeded internal drainage.  Organic matter properties such as lignin content and C:N ratio influence the microbial degradation processes, and as a result might affect the nature of redox features formed in wet soils.  In this study, effects of organic matter additions on soil redox feature formation were evaluated in undisturbed soil cores (mesocosms) using a time series experiment. Five different types of organic materials were evaluated by uniformly mixing each within the upper 10 cm of the soil using a rate of approximately 1.65 kg C m-2.  In addition, two of the organic materials were added to other mesocosms (on soil surface or concentrated in deeper zones) to further evaluate the effect of the application/incorporation method.   Mesocosms were subjected to simulated wetland hydrology (periods of saturation followed by periods of aeration).  Soil redox potentials (Eh), pH, and soil temperature were monitored throughout the experiment.  During the first wet-dry cycle (approximately 4 months), mesocosms began to develop observable hydromorphic features.  A few prominent  iron concentrations formed in macropores that were created either by redox electrodes or during pH sampling.  However, most of the features observed were very fine and faint concentrations.   Redoximorphic features were least evident in cores that had been mixed (where natural structure had been destroyed) and were most evident in cores that had organic materials concentrated into deeper zones. Different types of organic materials did not appear to significantly affect size, color or abundance of redoximorphic features that formed. It appears that the iron oxide concentrations are increasing in abundance over time.  A comprehensive data set and statistical analysis will be presented.