What is a common effect of herbicide application on soil microorganisms?

Herbicide application can lead to a reduction in microbial activity in the soil. Many herbicides are designed to kill or inhibit the growth of certain plants, and in the process, they can also have adverse effects on non-target soil microorganisms. These microorganisms play a crucial role in soil health, nutrient cycling, and organic matter decomposition. The introduction of herbicides can disrupt their populations and reduce their overall activity, which can ultimately affect soil quality and ecosystem balance.

In contrast, the other options suggest positive effects or neutrality concerning soil microorganisms. However, studies and observations indicate that herbicide exposure typically leads to unfavorable conditions for these beneficial organisms, thereby confirming the likelihood of a decrease in their activity.