Impact of Agrochemicals Used in Maize Crop on Selected Soil Biota

Field and laboratory experiments were conducted to examine the impact of agrochemicals on soil biota and on earthworms. Results from the field experiment showed that lambda-cyhalothrin (@ 500 ml/ha) increased the bacterial population to 151 x 10(6)CFU compared to the control plot with a population of 148.4 x 10(6)CFU. In contrast, the lowest population (78.5 x 10(6)CFU) was recorded in the mancozeb-treated plot (@ 500 g/ha), showing a higher negative impact on the bacterial population than other treatments. In fungi, the lowest population (44.8 x 10(3)CFU) was recorded in the mancozeb-treated plot, showing a high negative impact on the fungal population, followed by the nicosulfuron-treated plot (@ 50 g/ha) with a population of 76.5 x 10(3)CFU. The highest population was demonstrated by the control plot (121.9 x 10(3)CFU) followed by the lambda-cyhalothrin-treated plot (82.2 x 10(3)CFU), showing a less negative impact than the other treatments. Results from the laboratory experiment demonstrated significantly different effects of agrochemicals on earthworms in terms of mortality. Lambda-cyhalothrin proved more toxic compared to other chemicals with a maximum mean mortality of 56, followed by mancozeb with 45 and nicosulfuron with 33.3. Overall, lambdacyhalothrin was found to have no impact on bacteria, moderate impact on fungi, and high impact on earthworms, while mancozeb had a high negative impact against bacteria and fungi but had less impact on earthworms compared to lambda-cyhalothrin. Nicosulfuron had moderate impact against all the soil biota.