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Home HortTechnology Modified Switchgrass Promising for Use as Nursery Substrate
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WOOSTER, OH - Switchgrass (Panicum virgatum) biomass is being evaluated as a potential alternative to pine bark as the primary potting component in containerized nursery crops. While the perennial grass is a promising natural alternative, one of the problems with switchgrass and other grass-based substrates is that the pH is 7 to 7.5 - higher than is commonly recommended for nursery crop production.

"Substrate pH could be lowered in switchgrass substrates by amending with other physical components that have lower pH. It is also possible that the addition of organic substrates might reduce and buffer substrate pH over time," says a new study from U.S. Department of Agriculture‚ÄďAgricultural Research Service scientists James E. Altland and Charles Krause published in HortTechnology. The team determined the effect of sphagnum moss, municipal solid waste compost (MSC), and elemental sulfur (S) on pH of substrates composed primarily of switchgrass and evaluated subsequent plant growth. "Our approach was to initially use a short-production cycle annual crop to determine the immediate impacts of the amendments, followed by a long-term woody crop to document long-term effects on pH, pH buffering, and plant growth," said Altland.

Altland and Krause conducted three experiments. In the first two, annual vinca was used to quickly assess how pH was affected by the three amendments; the final experiment was conducted with blueberry to assess the long-term effects of substrate amendments.

"Summarizing across the three experiments, elemental S was effective in reducing substrate pH; however, rates 1 lb/yard3 or greater reduced pH below the recommended level of 5.5 and lower S rates did not maintain lowered pH over time," Altland noted. "Sphagnum moss and MSC together at 20% and 10%, respectively, were effective at reducing substrate pH and buffering against change." He added that sphagnum moss and MSC provided the additional benefit of improving physical properties of the switchgrass substrates by decreasing air space and increasing container capacity.

When using switchgrass substrates, addition of up to 20% peatmoss and 10% municipal solid waste compost is recommended for improving physical properties, moderating and buffering pH, and improving crop growth. "Nursery growers in Ohio already amend pine bark with ~20% peatmoss and ~10% MSC; thus, this aspect of substrate management would not be affected if growers changed to switchgrass-based substrates," Altland concluded.


The complete study and abstract are available on the ASHS HortTechnology electronic journal web site:

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Original Article:

Modification of Switchgrass Substrate pH Using Compost, Peatmoss, and Elemental Sulfur
James E. Altland and Charles Krause
HortTechnology 20:950-956. [Abstract][Full Text][PDF]

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