EVALUATION OF SELECTED PLANT MATERIALS FOR THE INHIBITION OF CARBON AND NITROGEN CYCLING ENZYMES

Abstract

Increasing total greenhouse gas emissions poses treats to global food security and livelihoods. Previous attempts to mitigate greenhouse gas emissions has focused on manipulating farm management practices. Manipulation of microbial and enzyme activities for this purpose has not receive much research attention. Laboratory experiment was conducted to evaluate selected plant materials for their abilities to inhibit the activities of carbon and nitrogen cycling enzymes. The selected plants used for this study are (Aloe vera, turmeric, moringa, ginger and garlic) raised in pots for three months in the screenhouse of the Department of Crop, Soil and Pest Management, Federal University of Technology, Akure, Nigeria. The selected medicinal plant extracts and Rhizosphere soils of the plants were evaluated in the laboratory using a complete randomized design (CRD). The following parameters were measured weekly, soil basal respiration, microbial biomass carbon (substrate induced respiration), while soil nitrogen and carbon enzymes, organic carbon, soil pH, microbial population were also evaluated and nitrification was determined at 14th and 22nd day after incubation. Results obtained from the Laboratory experiment showed that, extract from all the medicinal plants inhibited carbon mineralization judging by the amount of CO2-C produced in the first 3 weeks of incubation. Inhibition of carbon mineralization in the rhizosphere soil of the tested plant appear to be transient when considered exsitu. Activity of β-glucosidase enzyme was however inhibited by Aloe vera and garlic extracts, and the rhizosphere soils of moringa and garlic. Among the nitrogen cycling enzymes, urease activity was found to be inhibited by all the plant extracts while urease inhibition was only noticed in the rhizosphere soils of garlic and turmeric. Inhibition of amidase, L-asperginase and L-glutaminase activities were observed in soil samples treated with extracts from ginger, garlic, turmeric and moringa, respectively. The activity of Amidase, L-asperginase and L-glutaminase were also reduced at the rhizosphere soil of garlic and Aloe vera.All the extracts inhibited nitrification at 14th day after incubation and the inhibitory effect was sustained up till 22nd day except in the Aloe vera treatment. Stimulation of nitrification occurred in the rhizosphere of the plant on the 14th day after incubation except in garlic while nitrification inhibition occurred on the 22nd day after incubation. The selected plant extracts and rhizosphere soil improved soil pH and soil organic carbon also increased except for moringa extract. Inhibition of microbial population occurred by the extracts and rhizosphere soil. In conclusion, garlic appeared to be the most potent inhibitor of some of the products of soil processes determined in this study which are connected with greenhouse gas emission. The inhibitory activity of garlic was however closely followed by that of ginger. It is recommended that the selected plants be intercropped with either arable or plantation crops or introduced as fallow plants, the whole plants or part of their parts may be processed and used as additives to convectional fertilizer to serve the purpose of environmental conservation.