Nav: Home

Compost establishes growing media pH similar to limestone

November 28, 2016

KENNETT SQUARE, PA - As concerns increase about the environmental impacts of harvesting peat and the rising costs of peatmoss used as a growing substrate, researchers are seeking feasible alternatives. Compost can be used as a replacement for peatmoss, but issues such as phytotoxicity, high concentration of heavy metals, chemical carry over, high salts, and high pH have limited its use in the industry. The authors of a study in the September 2016 issue of HortScience studied the pH buffering capacity of substrates produced with compost and found that compost can be used to establish growing substrate pH similar to limestone, with "little to no effect on pH buffering capacity."

Matthew Taylor, lead author of the research, said there are many positive impacts of using compost in horticultural substrates. "Compost is created from recycled materials and places them back into the production stream," Taylor noted. "Compost can provide supplemental nutrition, may suppress disease-causing organisms, and can be used as a limestone substitute for pH establishment. Because of the high pH of most composts, limestone rates can be reduced or even eliminated when compost is used as a component of substrate or as a peatmoss replacement."

Taylor and coauthors Rachel Kreis and Lidia Rejtö said that determining the pH buffering capacity of substrates produced with compost is important for pH control and high-quality crop production. The scientists designed experiments to determine the resulting substrate pH when using a range of compost and limestone rates, and then compared the pH buffering capacity of substrates that had the pH established by the addition of compost, limestone, or a combination of both. Compost made of horse manure and bedding:wood chips:and a variable mixture of green plant material and restaurant food waste was used in all experiments (at a 1:1:1 ratio by weight).

The first experiment featured five compost rates (0%, 10%, 20%, 30%, and 40% by volume), and four limestone rates (0, 1.2, 2.4, and 3.6 g·L-1 substrate) in five replications. The experiment was conducted three times, each time using a different batch of compost. "With 0 lime, initial substrate pH increased from 4.5 to 6.7 as compost rate increased," the authors said. "This trend occurred at all other lime rates, which had pH ranges of 5.2-6.9, 5.6-7.0, and 6.1-7.1 for rates of 1.2, 2.4, and 3.6 g·L-1 substrate, respectively. Substrate pH increased significantly as either compost or lime rates increased."

The second experiment used four compost rates by volume (0%, 10%, 20%, and 30%) and the same four limestone rates as in the first experiment. Each substrate treatment was titrated through incubations with six sulfuric acid rates. "Substrates with a similar initial pH had very similar buffering capacities regardless of the compost or limestone rate," the authors said.

The experiments demonstrated that compost (with properties similar to the material used in the study) can be used in the same fashion as lime. "When compost is used in this fashion, lime will need to be applied at lower rates or eliminated to achieve the target pH, and growers can anticipate a similar pH buffering capacity," the authors added.

"Growers still need to consider that not only will pH buffering be influenced by the substrate composition, but also by the type of fertilizer, specific crop, and water alkalinity," Taylor added. "It should also be understood that all composts are not created equal. Proper chemical and physical tests must be done to ensure the compost is used properly."
The complete study and abstract are available on the ASHS HortScience electronic journal web site: in 1903, the American Society for Horticultural Science (ASHS) is the largest organization dedicated to advancing all facets of horticultural research, education, and application. More information at

American Society for Horticultural Science

Related Research Articles:

More Research News and Research Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: The Power Of Spaces
How do spaces shape the human experience? In what ways do our rooms, homes, and buildings give us meaning and purpose? This hour, TED speakers explore the power of the spaces we make and inhabit. Guests include architect Michael Murphy, musician David Byrne, artist Es Devlin, and architect Siamak Hariri.
Now Playing: Science for the People

#576 Science Communication in Creative Places
When you think of science communication, you might think of TED talks or museum talks or video talks, or... people giving lectures. It's a lot of people talking. But there's more to sci comm than that. This week host Bethany Brookshire talks to three people who have looked at science communication in places you might not expect it. We'll speak with Mauna Dasari, a graduate student at Notre Dame, about making mammals into a March Madness match. We'll talk with Sarah Garner, director of the Pathologists Assistant Program at Tulane University School of Medicine, who takes pathology instruction out of...
Now Playing: Radiolab

What If?
There's plenty of speculation about what Donald Trump might do in the wake of the election. Would he dispute the results if he loses? Would he simply refuse to leave office, or even try to use the military to maintain control? Last summer, Rosa Brooks got together a team of experts and political operatives from both sides of the aisle to ask a slightly different question. Rather than arguing about whether he'd do those things, they dug into what exactly would happen if he did. Part war game part choose your own adventure, Rosa's Transition Integrity Project doesn't give us any predictions, and it isn't a referendum on Trump. Instead, it's a deeply illuminating stress test on our laws, our institutions, and on the commitment to democracy written into the constitution. This episode was reported by Bethel Habte, with help from Tracie Hunte, and produced by Bethel Habte. Jeremy Bloom provided original music. Support Radiolab by becoming a member today at     You can read The Transition Integrity Project's report here.