Biostimulation of Atrazine-impacted Soil Using Cassava Peel Waste Considering the Associated Soil Bacteria

Abstract

The biostimulation of atrazine-impacted soil using cassava peel waste (CPW) considering the associated soil bacteria was assessed over a period of seven (7) weeks. The study was carried out at the Teaching and Research Farm of the Faculty of Agriculture, University of Port Harcourt, Port Harcourt, Rivers State, Nigeria. The aim of this work was to enhance indigenous soil bacteria in the biodegradation of atrazine through biostimulation using organic wastes. To achieve this, the physicochemical properties of the soil (before and after treatments) and the basic proximate mineral elements of the organic waste was determined before application using standard analytical methods. The bacterial characteristic and pH of the soil treated with CPW, CPW+ATZ, ATZ, and CONTROL (no treatment) were assessed using culture-dependent and standard analytical technique respectively. The study provided adequate evidence that the study site was naturally endowed with requisite bacteria (Acinetobacter sp., Enterobacter sp., Pseudomonas sp., and Bacillus sp.) with potential enzyme repertoire for atrazine degradation.  The addition of organic amendment improved the physicochemical status of the impacted soil which culminated to significant (P<0.05) increase in soil microbial population and diversity. The study also showed that pollutants (atrazine) at a tolerable level can improve bacterial population (as a result of the proliferation of naturally selected degraders) but reduce bacterial diversity. This was observed in the treatment, ATZ which had the least bacterial diversity but with the highest bacterial density (35.00±4.24×108cfu/g) at week 6. Although some bacteria are good degraders of herbicides in the soil, however, it may require some amendments in order to stimulate them to degrade pollutants. This work showed that the organic waste used in this study was a potential stimulatory agent that enhanced the growth of indigenous atrazine-degrading soil bacteria; hence can serve as an improved method of waste management and potential soil remediation approach.