3rd place 2017 UMD Three Minute Thesis Winner Sarah Hirsh


– When we buy our food
at the grocery store, we look at the price tag,
but we don’t usually think about the cost that growing
food has on the environment. What if we could grow food that had less of an environmental impact while at the same time saving farmers money. Crops need nutrients to
grow and be productive. That’s why we apply fertilizer. They need more nitrogen
than any other nutrient. Nitrogen readily moves through the soil. That makes it accessible to growing crops, but it can also leach downward into the groundwater and
out into bodies of water. In estuaries, such as the Chesapeake Bay, nitrogen inputs can
cause serious problems, such as massive die offs of shellfish or a buildup of toxic algae that can be harmful to human health. Corn and soybean agriculture
tend to leak nitrogen. First, they’re only growing
from May through August. That leaves most of the year where there’s no crop taking up nitrogen. Second, corn only uses about half of the nitrogen fertilizer
that’s applied to it. So the first question I asked is how much nitrogen is left at the end of the corn and soybean growing season? To find out, I took deep
soil cores on 25 farms across Maryland and Pennsylvania. I found huge pools of nitrogen. The amount of nitrogen I
found was two times the amount that a farmer would typically
applied to a corn crop. If farmers could capture and
recycle this pool of nitrogen that’s already in their soil, they could save big on fertilizer costs and at the same time prevent this nitrogen from polluting bodies of water. So I began investigating how
to use deep-rooted plants planted in the fall to capture and recycle this pool of nitrogen. First, I buried a nitrogen isotope tracer, basically a way to
track how nitrogen moves from the soil to the plants. Next, I planted radish and rye. If I planted the radish
and rye by early September, they quickly grew deep
roots and captured nitrogen from six feet deep by December,
but early planting was key. If I planted them in October, they would only capture
nitrogen from two feet deep. Next, I took this practice to the farms. Over 20 farmers
volunteered to plant trials of radish and rye. We had similar results, where if the radish and rye
was planted by early September they would capture deep-soil nitrogen. Furthermore, the radish
would die over the winter and decompose, releasing its
nitrogen on the soil’s surface. Now, the nitrogen’s at the
right place and the right time to be used by the following corn crop. This is a straightforward practice, essentially letting plants
do what they’re good at. Plants scavenge leftover nitrogen, which keeps it out of bodies of water. Next, the plants die and
release this nitrogen on the soil’s surface,
which provides a free form of fertilizer for the following crop. We end up with a win-win
situation for crop production and for water quality. Thank you.

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