Evaluating modified Organoclays using Magnetite Nanoparticles and Bacterial Exopolysaccharide and their Effects on Urease, Phosphatase, and Dehydrogenase Soil Enzymes

Soil enzymes are involved in processes such as decomposition of organic matter, food chain cycle, and degradation of contaminants. Therefore, it is very important to protect activity and stability of soil enzymes. This research was conducted at Ferdowsi University of Mashhad in 2017. In the present study, two types of organo-montmorillonites were produced by intercalating montmorillonite with magnetite nanoparticles and with an exopolysaccharide. The properties of the produced organoclays were studied using XRD and scanning electron microscopy (SEM). Effects of application of organo-montmorillonites to the soil on activities of urease, phosphatase, and dehydrogenase were investigated. The experiments were carried out using the completely randomized design with factorial arrangement employing four clay types (montmorillonite, NMM or montmorillonite intercalated with magnetite nanoparticles, ENMM or montmorillonite intercalated with both the exopolysaccharide and magnetite nanoparticles, and the control) at five durations (1, 3, 7, 14, and 21 days) with three replications. SEM images revealed that the best morphological changes happened in ENMM. Morphology images of this organoclay showed that it had small layers with abundant pores, the exopolysaccharide surfactant completely separated the clay layers and created abundant pores thus preventing nanoparticle aggregation. Results of the statistical analysis indicated that adding MM, NMM, and ENMM to the soil increased urease activity by 1.4-, 1.5-, and 3-fold, respectively. Moreover, activity levels of phosphatase enzyme increased by 1.1-, 1.3-, and 1.5-fold when MM, NMM, and ENMM were added to the soil, respectively and dehydrogenase activity increased by 1.1-, 1.2-, and 1.3-fold when MM, NMM, and ENMM were applied to the soil, respectively. Results indicated that the change in the soil environment surrounding the enzymes with the exopolysaccharide surfactant and magnetite nanoparticles increased activity and stability of enzymes in soil during the 21-day incubation period.