Effect of added organic substrates on reduction in a soil from the Maputaland Coastal Plain

Abstract

Wetland soils of the Maputaland Coastal Plain do not exhibit the redox morphology typically associated with extended periods of water saturation. The aim of this paper was to determine if the addition of various organic substrates (buffalo grass, peat, sucrose) would stimulate reduction of a selected soil from the Maputaland Coastal Plain. Results showed that the added buffalo grass and peat did not impact on reduction, irrespective of the amount added and were probably not readily oxidisable. Added sucrose was readily oxidisable and the amount applied significantly promoted reduction. Increased levels of the added organic substrates had a smaller effect on reduction. Higher total carbon levels (1.0% and 1.5%) typically resulted in lower pH and Eh, and higher Fe2+ concentrations. Generally, pH and Eh both declined during the first 14 days of water saturation, with a concomitant increase in Fe2+, followed by an increase in pH and Eh and concomitant decrease in Fe2+ over the next 28 days. It was concluded that the soils of the Maputaland Coastal Plain do not have enough residual organic carbon to support reduction and that a deficiency in readily oxidisable organic matter substrate should be further explored as cause for the absence of redoximorphic features in these soils.