AMES, Iowa – Researchers with Iowa State University Extension and Outreach have recently completed a three-year study of a soil amendment product known as biochar.
Their goal was to find out if this black, charcoal material could improve the production of certain vegetables commonly grown in Iowa. The results have not shown a major impact just yet, but researchers believe there may be long-term benefits to adding biochar, especially to degraded soils and soils prone to nutrient loss.
Biochar is produced from heating biomasses like wood, corn husks and poultry manure, with limited oxygen supply, in a process called pyrolysis.
Biochar can also be derived as a byproduct of biofuel production, and can be made from a wide range of biomass material, including switchgrass, mixed woods, rice hulls and oakwood, as well as animal and municipal wastes.
Cauliflower and red pepper
Taylor Mauch, graduate research student, began experimenting with biochar in 2020 by adding it to the soil in vegetable plots at Iowa State’s Horticulture Research Station in Ames. Her research focused on cauliflower and red bell pepper, and joins previous Iowa State research in carrots and potatoes.
Mauch had hoped to see an increase in yield as well as an improvement in soil structure and nutrient retention. Biochar research in agronomic crops like corn and soybeans have shown an increase in yields, improved water holding capacity and improvements in soil structure.
While her results have not shown a significant improvement on yields, she said there was also no signs of yield loss. The benefit of adding biochar, according to Mauch, could be the long-term improvements to soil.
“Biochar has the potential to be a storage container for nutrients, which could potentially influence the availability of nutrients to plants,” said Mauch.
The higher cation exchange capacity of biochar allows soils to retain more nutrients, including phosphorus. Biochar can also stimulate microbial activity, which helps microbes break down nutrients within the soil at a faster rate.
Her initial results appear to show a reduction in nitrate leachate from biochar-amended soils. This is an environmental benefit, and also keeps more nitrogen in the soil, available for crop uptake. Nitrogen leachate was tested using a lysimeter – a measuring device used to measure nitrate movement below the plant root zone.
“Taylor’s work helps us understand the potential use of biochar in vegetable cropping systems,” said Ajay Nair, associate professor in horticulture and an extension vegetable production specialist at Iowa State. “It highlights optimum biochar application rates in high organic matter soils and illustrates its impact on soil properties and crop growth and development.”
Improving topsoil takes time, and most healthy soils are not built nor lost overnight. Mauch acknowledges that her three years of research may not be enough to fully capture the potential of biochar, but she believes it’s a starting point.
“If people are going to apply biochar in Iowa, I think it would be for the long-term benefits,” said Mauch. “When we think about how much soil erosion is occurring and how much topsoil we are losing, products like biochar could be part of the solution.”
She explains her research in a series of short videos. The first is called Biochar in Vegetable Production Systems, and the other two are called How to Harvest Red Peppers and How to Harvest Cauliflower.
In the fall of 2022, Mauch and Nair also produced an extension publication called “An Introduction to Biochar and its Potential Use,” which defines how biochar is produced, how it can be applied to spoils, and the potential for long-term benefit.
This work was supported by the USDA NIFA Hatch Project and Iowa vegetable growers. Learn more by visiting the ISU Extension and Outreach Sustainable Vegetable Production website.