Can Adding Carbon to the Soil Help us Manage Weeds?

Maria Gannett

2019-2022 FFAR Fellow

Cornell University

  • Soil Health

Challenges Faced by Growers

If you have ever gardened or worked on a farm, you know that there is never a year without weeds. Providing crops the space and resources they need to grow without competition from other plants is a constant struggle. Despite the seeming futility of managing weeds, they cannot just be left unchecked. It is estimated that if weeds were left uncontrolled across the United States and Canada, corn and soybean yields would decrease by 50 percent, resulting in a loss of $43 billion. Organic growers, who cannot use synthetic herbicides to control weeds, have an especially difficult time managing weeds. Many organic growers are heavily reliant on tillage for weed control and while this can be very effective, too much tillage can lead to soil degradation over time. But what if there was a non-herbicidal way to both manage weeds and improve soil health at the same time? This is the subject of my research as a Ph.D. student at Cornell University.

Maria shoveling soil.

Developing Tools for Weed Management

Soil is alive with microorganisms and keeping the soil microbial community healthy is key to plant growth. But how exactly are soil microbes and plant growth related?  And how might we use this knowledge to develop a useful weed management tool for growers? These are the fundamental questions my research is seeking to answer.

One way that the microbial community and plant growth are tied together is through the presence of carbon and nitrogen in soils. Carbon stimulates the growth of soil microbial communities. As these soil microbes grow, they also take up soil nitrogen. This process, known as nitrogen immobilization, leaves less nitrogen available for plants, including weeds. Many of our most problematic agricultural weeds grow well in high nitrogen soils and are less competitive in soils with low available nitrogen levels. Managing soils so that they have lower nitrogen levels could thus be one way to combat weeds without tillage or the application of herbicides. To test this hypothesis, we are adding high carbon amendments to the soil, such as sawdust or straw, planting different crops and then monitoring the growth of the soil microbial community, weeds and the crop.

Since carbon stimulates the growth of soil microbes, the second potential benefit of added carbon is improved soil health. Soil microbes are crucial to most aspects of soil functioning such as soil organic matter formation, nutrient cycling and soil structure formation. After just one year of our study, we are already seeing small improvements in soil health traits and reduced weed growth in some soils amended with carbon. We hope that by better understanding this link between high-carbon amendments, soil microbial communities and plant competition, we can develop this technique into a tool that will help farmers manage weeds on their farms and improve their soil health simultaneously.

Expressing Gratitude

At the same time that I am exploring these scientific theories, participation in the FFAR Fellows program has given me the resources to develop as a professional. It has expanded the scope of my Ph.D. from an understanding of how the plants and soils of my research work together, to include an understanding of how people work together. With the onset of climate change and the stressors of learning to share our limited resources, making science accessible to everyone will be more important than ever. It is through programs like the FFAR Fellows that the future leaders in science will be prepared to meet that challenge. I am forever grateful to my industry sponsor, AMVAC Chemical Corporation and my FFAR Fellow peers and mentors who have made this opportunity possible for me.

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