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With a $1.7 million grant from the National Science Foundation, Penn State researchers will investigate how duckweed could be grown on Pennsylvania farms to reduce nutrient pollution in Chesapeake Bay.
Duckweed, a small plant resembling a lily pad, grows rapidly in water with elevated levels of nitrogen and phosphorus, often as a result of fertilizer and manure runoff. While many regard the plant as pests, farmers may find duckweed doubly beneficial, according to Rachel Brennan, associate professor of environmental engineering and principal investigator of the project.
Not only can duckweed trap the nutrients before they cause problems such as algal blooms and dead zones, but it can also "upcycle" those nutrients into something that farmers can reuse," Brennan said. "It can be harvested several times a week and used as a nutritional supplement for farm animals. We've also shown that it can be used as a soil modification to support crop growth with far less runoff than conventional fertilizer. Duckweed has tremendous potential to take a waste product and give it greater value".
In a preliminary assessment, Brennan's team calculated an estimated economic return for farmers if they reallocated part of their land from growing soybeans - often used for animal feed - to a pond to grow duckweed. By mixing manure with water in the pond instead of applying it to an open field, the farmers could not only reduce their waste, but also produce more protein.
"Soybeans contain a huge amount of protein, but they don't grow very fast," Brennan said. "The protein content of duckweed is high and so is the growth rate, so it has a higher yield. Given the same area, you can produce more protein if you switch to this small aquatic plant.
In the four-year project, a multidisciplinary series of experiments will evaluate both the ecological and economic benefits of the team's duckweed proposal. Co-researchers of the project include Lauren McPhillips, assistant professor of civil and environmental engineering and agricultural and biological engineering; Wayne Curtis, professor of chemical engineering; Alexander Hristov, leading professor of dairy food; and Christine Costello, assistant professor of agricultural and biological engineering.
The team will first work with Matt Royer, director of the Penn State Agriculture and Environment Center, and Penn State Extension dairy consultants to examine local dairy farmers on their first impressions of the proposal. Dairy farming makes up a significant portion of the farms in Pennsylvania, which covers 35% of the Chesapeake Bay watershed area.
"For this to work, it must be economically advantageous for the farmers," says Brennan. "They shouldn't have to buy so much chemical fertilizer or feed because they can take their own waste foods, turn them into duckweed and then re-use them.
Some of the experiments in the project focus on the performance of duckweed as a nutritional supplement, including how well the cows digest the plant and its impact on milk production, as well as ways to improve both.
Others will investigate the effects of duckweed as a fertilizer. According to McPhillips, there are indications that it could not only reduce the amount of nutrients in the drainage, but also reduce nitrous oxide emissions, the third most common greenhouse gas.
"An important goal of this project is to leverage duckweed to help reduce harmful nutrient losses of any kind," she said. "A less considered pathway is the loss of nitrous oxide, which can be produced by microbes in the environment. Generating soil and feed supplements on site also reduces energy consumption and greenhouse gas emissions that would otherwise have been needed to produce and transport them to the company".
The team also plans to look at the proposal from a holistic perspective, brainstorming on ways in which a "circular bioeconomy" based on duckweed can be sustainably scaled up outside local farms.
"Collecting biomass from fields to make ethanol in central processing plants is an established practice, and perhaps a similar approach to collecting manure from farms could be used to produce duckweed," Brennan said. ", "It could be grown vertically in large warehouses because it only needs about an inch of water to grow. It would be a big change, but any big transformation to agriculture will seem radical at first.
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