Weed management is one of the greatest challenges faced by organic farmers, who can't use herbicides. They rely on tillage for weed control, but tillage often is less effective than herbicides or other conventional forms of weed management. As a result, weeds reduce yields in organic systems. To better equip organic farmers to control weeds, a team of Penn State agricultural scientists received a four-year, $935,000 grant from the U.S. Department of Agriculture to study how promoting soil microbes to infect and kill weed seeds might reduce problematic weed species.
"We expect our research to identify specific groups of microorganisms such as bacteria and fungi that are associated with greater mortality of weed seeds," said research team leader Carolyn Lowry, assistant professor of plant science in the College of Agricultural Sciences. "Ultimately, our research will result in a greater understanding of how to use ecological approaches to manage weeds in organic systems by leveraging microorganisms for biological control."
The researchers will conduct two complementary experiments - one in field crops and one in vegetables - examining how organic soil amendments influence both weed seed mortality and the soil microbiome, which is the vast, diverse community of microorganisms such as bacteria, fungi and single-celled microorganisms called archaea living in soil. To do this, they will compare organic soil fertility amendments - materials such as compost, manure or lime mixed into soil to enhance its physical, chemical or biological properties - that vary in chemical and nutrient quantities.
Additionally, in a separate effort, the team will leverage one of Penn State's long-term organic crop diversity experiments to evaluate how distinct perennial forage crops - compared to a standard organic annual crop rotation - influence weed seed mortality and the soil microbiome. They will use a cost-effective technique that to analyze targeted genetic variations and mutations in microbial communities to characterize the bacterial and fungal communities within weed seeds. The researchers also will use biochemical tests that enable them to determine whether seeds are alive or dead.
Through these experiments conducted on farms as well as on research plots at Penn State's Russell E. Larson Agricultural Research Center, the researchers aim to determine the drivers of weed seed mortality and microbiomes.
"Finally, in collaboration with organic farmers, we will use our farmer advisory panel, on-farm trials and other extension events, as well as extension publications, to develop a mutual understanding of how soil fertility and crop rotations can be leveraged within organic systems to enhance weed seed mortality in the soil," Lowry said.
Other members of the research team include: Estelle Couradeau, assistant professor of soils and environmental microbiology; Sharifa Crandall, assistant professor of soilborne disease dynamics and management; Elsa Sánchez, professor of horticultural systems management; and extension educators Ashley Isaacson and Ryan Spelman.
