Impact of leonardite amendments on soil physical properties of two soils related to grain production

Abstract

One of the major constraints to crop productivity is soil structure. A soil with good structure will have an optimum balance of pores conducive to infiltration, aeration and water retention. Soil structure can be changed with amendments and field management. The objectives of this thesis were: (1) to evaluate the effectiveness of leonardite amendment application on improving soil structure; (2) to determine whether leonardite application has the ability to improve crop productivity. The evidence obtained suggests that the given forms of leonardite (an oxidized lignite) were ineffective in improving soil structure and crop productivity. Upon initial field application, the hydrophobic nature of the material was realized. This water repellency was carried over to the second field season. Leonardite was ineffective in altering soil porosity, soil strength, and water stable aggregation following one field season. Residual treatment effects evaluated following the next growth season showed there were no significant differences. Crop yield was also not affected by field applied leonardite. Due to the hydrophobic nature of the leonardite, it was suspected that there were little to no active functional groups on the surface of the leonardite. This was suspected to be the reason that leonardite was ineffective in altering soil structure. An incubation study using a soluble powder form of leonardite resulted in no treatment effect on aggregate stability or crop productivity. The incubation study revealed an increase in the organic carbon content of the soil with increasing leonardite application. The chemical alteration of leonardite to a soluble form appeared to be ineffective in increasing the quantity of surface active functional groups involved on soil aggregation.