Evaluation of effects of animal dung composites and Bacillus sp in amended bioremediation of Zn-polluted soil on maize seedlings growth

Abstract

Heavy metal pollution of arable soils reduces their productivity, hence the need for ecofriendly techniques to ameliorate this increasing menace. In this study, cow dung, poultry wastes and their composites were applied as organic supplements, together with Bacillus sp as plant growth promoting rhizobacteria to amend bioremediation of zinc-polluted soil sample. Effects of amendments on physicochemical, mineral contents, and dehydrogenase activity of soil, as well as on corn seedlings growth rate, protein and chlorophyll contents and bioaccumulation of Zn were analyzed. Results demonstrated an increase in pH and nutrient contents including N, organic carbon, soil organic matter, K etc., of amended soil samples. Amendment with composite of two organic supplements produced highest increase in dehydrogenase activity, recording 2.35±2.04 µgTPFg-1h-1 at 33.75 mg/kg, and 2.19±0.04 µgTPFg-1h-1 at 52.55 mg/kg level of Zn pollution. Number of leaves recorded in most samples reduced with increasing Zn pollution, with seedlings grown on soil samples amended with cow dung alone outperforming others and recorded 10.3±0.5, 11.3±0.5 and 12.3±0.5 leaves at 32.75 mg/kg, 42.02 mg/kg and 52.44 mg/kg levels of Zn pollution respectively. Heights of seedlings in most of amendments also decreased with increasing Zn pollution. Also, seedlings grown on samples treated with cow dung alone were tallest, and recorded 109.0±3.4 cm, 115.8±4.3 cm and 127.3±2.6 cm at 32.75 mg/kg, 42.02 mg/kg and 52.44 mg/kg levels of Zn pollution respectively. Zn bioaccumulation different parts of corn seedlings was generally in the order; roots>leaves>stems, while it was; control samples>composite of poultry wastes and cow dung samples>only poultry wastes samples>only cow dung samples, for various treatments. This buttresses the usefulness of organic amendments, especially cow dung, in bioremediation of Zn-polluted soil used for agricultural activities.