Sir, for clarification do you want to measure crop injury from herbicide and allelochemicals since you mentioned crop ? or you are interested in evaluating the weed control efficacy of herbicides and allelochemicals?
Weedy check where no herbicide or allelochemical is applied is needed as standard for comparison. Application to bare soil may be useful to evaluate their effects on weed seed-bank and a bare soil with no application will serve as control.