Effect of two commonly used insecticides on some physico-chemical parameters and microbial load of a farm soil

Abstract

Pesticides are generally used in agriculture to eliminate un-wanted growths and reduce productivity cost with little concern for non-target organisms. Studies were carried out on the effect of two commonly used insecticides (common names-DD force & Scorpio) on some soil physicochemical parameters and microbial loads at recommended rate (x1.0) and twice the recommended rate (x2.0) over a period of 8 weeks. Generally, insecticides treatments resulted in soil pH reduction from 7.23 for the control soil to 5.98 for DD force and 7.03 for Scorpion. At recommended application rates (x1.0) there was a decrease in bacterial counts at week 0 (6 hours after treatment)-control soil = 6.90 x106 cfu/ml; DD force = 3.09 x106 cfu/ml and Scorpio = 3.09 x 106 cfu/ml. Thereafter, there was an increase in bacterial counts reaching a maximum at week 4. This was followed by a general decrease in bacterial counts. Bacteria counts in soils treated with DD force and Scorpio at twice the recommended rates (x2.0) were higher compared to counts obtained from the two insecticides treated at the recommended rates (x1.0). However, fungal counts from soils treated with the two insecticides at recommended rates (x1.0) were higher compared to counts obtained from soils treated at twice the recommended rates. A total of 55 bacterial species were isolated from the insecticide treated and control soils which are Bacillus sp (30.9%), Proteus sp (12.7%), Flavobacterium sp (14.5%), Pseudomonas sp. (1.8%), Lactobacillus sp (10.9%), Staphylococcus sp (10.9%), Antinomycetes sp (12.7%). A total of 20 fungi isolated were isolated from insecticides treated soil and control soil which includes Aspergillus sp (40%), Penicillium sp (20%), Rhizopus sp (20%)