The days of incubation had significant effect (P 0.001) (Table 5) on soil dehydrogenase activities. The results in Figures 5, 6 and 7 shows that as the days of incubation increased, the soil dehydrogenase activities also increased concomitantly to the 20th day. The results of the control samples showed higher increases than those of the herbicide treated soils which dropped upon treatment with herbicides. After the 20th day of incubation, glyphosate treated soils had the highest dehydrogenase activities of 11.49 and 20.16 µg (g-1min-1) at the second and sixth week, respectively, while prime-extra treated soils had the lowest after 20th day of incubation with values of 9.02, 12.55 and 16.09 µg (g-1min-1) after the second, fourth and sixth week, respectively.