Plant Biodiversity Increases Yields in Organic Intercropping System, Study Finds
COLLEGE STATION, Texas – Intercropping vegetable species that serve a specific role in production – from weed suppression to soil fertility to growth habit – improve crop yields over the entire system compared to a monoculture crop, according to results of a Southern Sustainable Agriculture Research & Education (SSARE)-funded study.
Jose Franco, a graduate student in the Department of Ecosystem Science and Management at Texas A&M University, along with Department of Horticultural Sciences professor Astrid Volder, manipulated functional species diversity in an organic intercropping system to determine whether a multi-layered agroecosystem improves per area yield.
“Research literature has shown that biodiversity in a natural ecosystem increases total plant productivity,” said Volder. “The combined species use the resources available to them in a more efficient way by avoiding intra-species competition. We wanted to test that idea in an ag system to see if we can use this concept to improve yield of the combined species per unit area.”
Franco said that the “three sisters” intercropping system of squash, beans and corn practiced by Native Americans is a perfect example of crops using functional elements to the benefit of the entire system.
“The squash suppresses weed growth, the bean is a nitrogen-fixer, and the corn is used as structural support because it grows tall,” said Franco. “I thought it was an interesting idea to explore several vegetable species with different functional roles to see how these species interact with each other compared to a mono-crop system.”
In the SSARE-funded Graduate Student Grant project, Franco chose okra as a pollinator attractant, peanuts and cowpea as nitrogen fixers, watermelon as a weed suppressor, and hot pepper for its allelopathic benefits. Five treatments of intercropped plants, where each plant was incrementally added to the system, were compared to five mono-crop treatments over two years.
The researchers found that, overall, crop yields increased on a per acre basis in the intercropping systems compared to the mono-crop treatments, with the most noticeable increases in per plant production in the watermelon-okra-peanut intercropping system.
“Research is needed on what specifically is happening, but we think that the plants are more efficiently using the resources available to them within their own ecosystem niche,” said Franco. “So their functional diversity – weed suppression, shade tolerance, insect suppression, for example – is a benefit to the community as a whole, rather than a hindrance.”
Said Volder, “Within a monoculture, it’s like you are competing against a clone of yourself, while in a diverse system you may be exploring different resources than your neighbor, thus reducing competition and potentially even benefitting from the positive traits of your neighbor.”
The researchers said that while some literature exists on companion planting, little information exists on using the functional diversity of plants in an intercropping system. So for farmers interested in trying out the technique, it’s going to take a bit of experimentation to find the right cropping combination.
“You want to pick vegetable crops that, of course, are suitable to your area, as well as choose crops that won’t compete against each other,” said Volder. “For example, for shade tolerance, pick a tall plant species, and pair a nitrogen fixer with a fast-growing crop.”
Franco is currently measuring the nitrogen rates captured in the soil from the peanuts and cowpeas.
Volder emphasizes that long-term research on various intercropping combinations is needed to see how plant interactions play out and to determine what exactly is happening in the soil.
“At minimum, this study highlights the importance of having a diverse cropping system that could assure producers would still have one or more cash crops to harvest when one component crop fails,” said Volder.
For more information on the results of the project, “Evaluating Functional Diversity in an Organic Intercropping System,” search the SARE Projects Database by project number GS11-108.
Published by the Southern Region of the Sustainable Agriculture Research and Education (SARE) program. Funded by the USDA National Institute of Food and Agriculture (NIFA), Southern SARE operates under cooperative agreements with the University of Georgia, Fort Valley State University, and the Kerr Center for Sustainable Agriculture to offer competitive grants to advance sustainable agriculture in America's Southern region.