The role of organic matter in soil manganese equilibrium

Summary Tests were conducted to determine the role of additions of fresh organic matter (ground cotton seed hulls) to an alluvial loam soil of pH 8 on manganese equilibrium. It was shown that organic matter has a reducing potential which, when added to the soil, resulted in a rapid and marked increase in exchangeable manganese. The reduction is enhanced by higher temperatures (21.1vs 37.7°C) and additions of water (field capacityvs air dry) and incubation periods up to 3 days. It is suggested that the shift in the soil manganese equilibrium, induced by such factors as waterlogging or anaerobic conditions, will be more pronounced when soils contain high levels of organic matter.Patterns of the standard deviations of sample exchangeable manganese data within treatments showed that the variance is highest in moist soil, lower concentrations of added organic matter, and at longer durations of incubation. Re-oxidation of manganese occurred at lower levels of added organic matter (2 and 4%) and extended incubation time (5 to 9 days).The investigation reported in this paper (67-10-36) is in connection with a project of the Kentucky Agricultural Experiment Station and is published by permission of the Director.