Pages: (49-60 )
Abstract
Farmers in Nigeria are mainly concerned with targeted effects of pesticides without attention to their secondary effects on the soil microbiological and physicochemical properties, which are crucial to soil fertility. Hence, these chemicals are indiscriminately applied. This study therefore investigates the effects of paraquat (1,1’-Dimethyl-4,4’- bipyridinium dichloride) and glyphosate(N-(phosphonomethyl) glycine), at the manufacturer’s recommended application rates and at doubled these concentrations, on soil physicochemical properties and microorganisms. Soil pH, organic carbon, nitrogen, phosphorus content and cation exchange capacity were determined. Microorganisms were isolated and enumerated using dilution plate method. The results obtained revealed no significant effect of the herbicides on soil physicochemical properties at P>0.05. Both herbicides significantly reduced microbial counts in the soil (as compared with the herbicide untreated soil).Fungal population reduced from 9.97±3.5 to 7.63±3.28 as compared to the bacterial population whose count showed almost no difference (1.67±1.41 to 1.65±1.32). Glyphosate had a higher inhibitory effect compared to paraquat. Bacillus, Pseudomonas, Aspergillus, Penicillium and Rhizopus were the most frequently isolated microbial genera. The study reveals that soil microorganisms may be adversely affected by the application of herbicides. This could be detrimental to the sustainability of soil fertility.
Keywords: Herbicides; physicochemical; microorganisms; soil; fertility.,