Effects of Two Commonly Used Herbicides on Soil Microbes and Organic Matter of Soil from Maize and Cocoa Plantation

Herbicide application had been an effective method of weed control over the years, however, the effect of herbicides on the non-target soil microbes that play roles in degrading organic matter and nutrient recycling needs to be considered. The effects of two (2) most commonly used herbicides in Osun State on soil microbes of maize and cocoa plantation were assessed over a period of thirteen continuous days (exposure period). The herbicide treatments were the normal recommended field rate, (0.72 mg active ingredient per gram of soil for 2, 4-D amine and 0.24 mg for glyphosate, double the recommended field rate, (1.44 mg of active ingredient per gram of soil for 2,4-D amine and 0.48 mg for glyphosate). The bacteria and fungi populations were then determined at a three-day interval up to the 13th day after treatment. Result indicated that herbicides treatment had a pronounced toxic effect on microbes population at 4 days after treatment however the toxicity gradually reduced as the exposure time increases. Double recommended field rate has higher toxic effect than the normal field rate. Also, glyphosate has less inhibitory effect on bacterial population than 2,4-D amine. Thus, glyphosate is recommended at the normal recommended field rate for maize and cocoa plantation.