I can't tell for certain if that's clover or not, but I can offer you the adaptive management we use for that group of plants: First of all, all clovers are not alike. Red clover, Alsike clover, et al are low-growing guys that, while tough competitors as all clovers are, are low-growing and subject to being shaded out by taller-growing species eventually. So not nearly so bad a problem as the next group-the sweet clovers. Those species, easily reaching five or more feet in height, will compete vigorously with what have you. We do two primary things to handle sweet clover. first, we will mow just as it is going into flower, thereby wasting its energy and disrupting one seed cycle. Then, we will spot spray where it's possible to do so. Sweet clover will quite easily ruin a prairie planting, so that's the one to really watch.

I get it though that you're worried about simply seed germination/plant elongation through that layer. But you can't really spray it out without hitting far too many prairie species, I would think. So work to favor the taller-growing stuff. Burning in spring will sometimes-if timing is right on-kill some of the early-greening clovers too, so that's a third method to consider. Of course, if you're not equipped to do a controlled burn, you may have to hire that out..

+oM