To better understand the mechanisms of allelopathy of Artemisia ordosica Spreng., we tested the hypothesis that allelochemicals from A. ordosica changes to K+ and NH4+ absorption in roots, thereby regulating the seed germination and seedling growth of associated plants [Agriophyllum squarrosum (L.) Moq., Corispermum hyssopifolium L., Astragalus melitodes Pall. and Setaria viridis (L.) Beauv.]. We found that allelochemicals (benzoic acid, butanedioic acid and hexadecanoic acid) from A. ordosica, were released into the surrounding soil and inhibited the seed gemination, root growth, shoot height and also decreased the dry mass of these associated plants. Conversely, A. ordosica extracts promoted the seed gemination and seedling growth of Setaria viridis grass. For the first time, we showed that the mechanism was related to ion adsorption by using non-invasive ion selective microsensors. These microsensor studies showed that the extracts of A. ordosica significantly decreased the root absorbtion of K+ and NH4+ for A. squarrosum, C. hyssopifolium and A. melitodes, but enhanced the root uptake of K+ and NH4+ in S. viridis. These results are imperative to understand the underlying mechanism of allelopathy between plants, which significantly impacts the dryland vegetation, wind shelters, water runoff and other ecosystem dynamics.