Bioremediation of residual fertilizer nitrate: II. Soil redox potential and soluble iron as indicators of soil health during treatment

The prospect of using wastewater containing high loads of soluble organic m atter (OM) for removing residual agricultural chemicals (fertilizer, pestic ide, or herbicide) in farm soil, although promising, could have adverse eff ects on soil agricultural quality as a result of development of redoximorph ic features in the soil profile. In this study, the effect of organic carbo n supplement for bioremediation of residual fertilizer nitrate on soil prop erties, redox potential (Eh), pH, and metal ion mobilization was studied us ing sandy soils packed in columns. The study was included in a general proj ect, described elsewhere (Ugwuegbu et al., 2000), undertaken to evaluate us e of controlled water table management (WTM) systems to supply organic carb on for creating a reduced environment conducive to denitrification of resid ual fertilizer nitrate leaching from the farm to subsurface water. The colu mns were subjected to subirrigation with water containing soluble organic c arbon in the form of glucose, The work was carried out in two experimental setups and the long-term effect of a range of glucose concentrations on the Eh, pH, and soluble levels of Fe and Mn was investigated. From the results obtained, it could be concluded that excessive organic carbon supplement t o soil can have adverse effects on soil quality and that Eh and soluble Fe are the two most practical parameters for monitoring soil health during tre atment of farm chemicals.