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United States Department of Agriculture

Agricultural Research Service


Location: Application Technology Research Unit

Title: Modification of Switchgrass Substrate pH Using Compost, Peatmoss, and Elemental Sulfur


Submitted to: HortTechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 13, 2010
Publication Date: December 21, 2010
Repository URL:
Citation: Altland, J.E., Krause, C.R. 2010. Modification of switchgrass substrate pH using compost, peatmoss, and elemental sulfur. HortTechnology. 20:950-956.

Interpretive Summary: Switchgrass (Panicum virgatum L.) is a perennial grass currently being developed for its biofuel potential. Our lab has been exploring the possibility of using switchgrass as a raw material for nursery container substrates. One of the problems with switchgrass and other grass-based substrates is that pH of these ground materials is higher than what is typically recommended for nursery crop production (4.5 to 6.5). Substrate pH could be lowered in switchgrass substrates by amending with other physical components that have lower pH (sphagnum peatmoss, for example). It is also possible the addition of organic substrates with high cation exchange capacity, in the form of compost or peatmoss, might reduce and buffer substrate pH over time. The objective of this research was to determine the effect of sphagnum peatmoss, municipal solid waste compost (MSC), and elemental S on pH of substrates comprised primarily of switchgrass and subsequent plant growth. Our approach was to initially use a short-production cycle annual crop (annual vinca) to determine the immediate impacts of the aforementioned amendments, followed by a long-term woody crop (blueberry) to document long-term effects on pH, pH buffering, and plant growth. Peatmoss and MSC decreased substrate pH of switchgrass to a level more conducive to annual vinca production. Elemental S was effective at reducing pH, but rates should be limited to less than 1 lb/yd3 and varied depending on the species being grown and its pH requirement. Combinations of peatmoss and MSC were more effective in buffering pH against changes than either component alone. Plant growth and quality were improved with additions of peatmoss and MSC but negatively affected with higher rates of elemental S (>1 lb/yd3). When using switchgrass substrates, addition of up to 20% peatmoss and 10% MSC is recommended for improving physical properties, moderating and buffering pH, and improving crop growth.

Technical Abstract: Switchgrass (Panicum virgatum) biomass is being evaluated as a potential alternative to pine bark as the primary potting component in containerized nursery crops. Substrates comprised entirely of switchgrass have higher pH than what is considered desirable in container substrates. The objective of this research was to evaluate the influence of elemental sulfur (S), sphagnum peatmoss, and municipal solid waste compost (MSC) as amendments for reducing substrate pH and buffering it against large changes over time. Three experiments were conducted, the first two using annual vinca (Catharanthus roseus ‘Pacifica Blush’) to quickly assess how pH is affected by the three amendments. The final experiment was conducted with blueberry (Vaccinium corymbosum ‘Duke’) 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/yd3 or greater reduced pH below the recommended level of 5.5 and lower S rates did not maintain lowered pH over time. Sphagnum peatmoss and MSC together at 20% and 10% (v/v) were effective at reducing substrate pH and buffering against change. Sphagnum peatmoss and MSC provided the additional benefit of improving physical properties of the switchgrass substrates.

Last Modified: 7/28/2014
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