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Title: Response of weeds and ornamental plants to potting soil amended with dried distillers grains

Author
item Boydston, Rick
item Vaughn, Steven
item Collins, Harold

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2007
Publication Date: 1/1/2008
Citation: Boydston, R.A., Vaughn, S.F., Collins, H.P. 2008. Response of weeds and ornamental plants to potting soil amended with dried distillers grains. HortScience. 43:191-195.

Interpretive Summary: Weeds lower the value of ornamental plants and their control increases the cost of ornamental plant production. Dried distillers grains with solubles (DDGS) is a byproduct of ethanol produced from corn and developing new uses for DDGS could increase the profitability of ethanol production. This research evaluated DDGS as a soil amendment to container grown ornamentals to suppress weeds. Adding DDGS to a commercial potting soil reduced emergence and growth of two common weeds; common chickweed and annual bluegrass. However, the concentration of DDGS required to suppress weeds was also injurious to transplanted rose, phlox, and coreopsis. Due to the injury observed on ornamentals transplanted into DDGS amended potting soil, subsequent studies evaluated surface-applied DDGS to suppress weeds. DDGS applied at 800 and 1600 g/m2 to the surface of transplanted ornamentals reduced number of annual bluegrass by 40% and 57% and common chickweed by 33 and 58%, respectively, without injury to transplanted ornamentals. DDGS may be useful for reducing weed emergence and growth in container grown ornamentals applied to the soil surface at transplanting.

Technical Abstract: Dried distillers grains with solubles (DDGS) is a byproduct of ethanol produced from corn and developing new uses for DDGS could increase the profitability of ethanol production. This research evaluated DDGS as a soil amendment to container grown ornamentals to suppress weeds. Adding DDGS to a commercial pine bark potting mix reduced emergence and growth of common chickweed (Stellaria media) at concentrations of 5 % (wt/wt) or greater and annual bluegrass (Poa annua) at concentrations of 10 % (wt/wt) or more. Herbicidal activity of DDGS was maintained in methanol-extracted DDGS. Rosa hybrid, var. 'Red Sunblaze', Phlox paniculata, var. 'Franz Schubert', and Coreopsis auriculata, var. 'Nana' transplanted into potting soil amended with 20% by weight DDGS were severely stunted and nearly all plants died. Most plants survived when transplanted into potting soil containing 10% DDGS by weight, but growth was greatly stunted and flowering of rose and coreopsis was reduced. Addition of 20% DDG decreased the C:N ratio from 90:1 to 24:1 for the potting mix and from 23:1 to 10:1 for a soil. The decrease in C:N ratio resulted in a 2-fold increase in microbial respiration at 3-d and 14-d of incubation for both the potting mix and soil. Due to the phytotoxicity observed on ornamentals transplanted into DDGS amended potting soil, subsequent studies evaluated surface-applied DDGS to suppress weeds. DDGS applied at 400 g/m2 or less to the soil surface at transplanting did not reduce emergence or growth of common chickweed or annual bluegrass. DDGS applied at 800 and 1600 g/m2 to the surface of transplanted ornamentals reduced number of annual bluegrass by 40% and 57% and common chickweed by 33 and 58%, respectively, without injury to transplanted ornamentals. DDGS may be useful for reducing weed emergence and growth in container grown ornamentals applied to the soil surface at transplanting.