Effects of changes in redox potential induced by flooding and organic matter interaction on plant nutrient elements availability, phosphorus and zinc adsorption in soils

Redox reactions affect both directly the redox elements and indirectly the availability and reactions of all other plant nutrients. In the first phase of this two-stage study, the effect of farmyard manure (FYM) applications (0, 4 t da-1) and flooding treatments (0, 7, 14, 21, 40 days) on nutrient availability in 10 soils were investigated by incubation experiment. The elemental composition of the drainage water, nutrient availability and pH, electrical conductivity (EC), oxidation-reduction potential (ORP) parameters were determined in the soil. In the second stage, 5 redox-sensitive soils were selected and the effects of flooding and FYM applications on zinc and phosphorus adsorption were investigated by batch sorption technique. The confirmation of data were statistically tested for Langmuir and Freundlich isotherms. It was found that the redox reactions increased the plant nutrient availability in the short-term due to changes in pH and dissolution of iron and manganese oxides and decreased it in the long-term due to secondary precipitation and adsorption reactions. Generally, the availability tended to increase until day 21 and then partially reached equilibrium. The application of FYM resulted in more severe redox and related reactions. The isotherms of soils were described by both isotherm models, but Langmuir isotherm showed better performance. FYM application generally increased the adsorption. This was considered as an indication of the contribution of FYM to soil buffer systems and its adsorption capacity. It is thought that the addition of ORP parameter to routine soil analyses is suggested for comparing the results in different periods.