Effects of soil calcium and pH on seed germination and subsequent growth of large crabgrass (Digitaria sanguinalis)

Large crabgrass is a problem weed in horticultural crops, particularly in t urfgrass in the southeastern United States. If growth of large crabgrass co uld be suppressed via soil pH or calcium levels, control of this weed in tu rfgrass might be improved while minimizing herbicide usage. To determine th e effect of soil calcium and pH on germination and growth of large crabgras s, seeds were sown in a loamy sand soil amended with calcium carbonate (CaC O3) or magnesium carbonate (MgCO3) that established a range of soil pH from 4.8 to 7.8. Seeds were also sown in soil amended similarly with calcium su lfate (CaSO4), which does not affect pH, that established a range of exchan geable Ca levels corresponding to the Ca range in CaCO3 from pH 4.8 to 7.8. Seed germination of large crabgrass was unaffected by pH when soil was ame nded with CaCO3, whereas seed germination decreased with increasing pH when soil was amended with MgCO3. Crabgrass germination was not affected by Ca (CaSO4) independent of pH changes. Increasing soil pH reduced shoot and roo t dry weights of seedlings regardless of material used to raise pH. Maximum shoot dry weights occurred at pH 4.8 in the unamended soil, whereas maximu m root dry weights occurred at ranges from pH 5.8 to 6.3 for CaCO3 and pH 5 .3 to 5.8 for MgCO3. Shoot and root dry weights were not affected by Ca whe n soil was amended with CaSO4. By raising soil pH levels, the growth of lar ge crabgrass and its ability to compete with turfgrass may be reduced. Rais ing exchangeable Ca does not appear to be an effective management tool for control of this weed species.