Hi! I am Emily Rehmann, and I am one of the high school interns for Water Rocks! and Iowa Learning Farms this year. I will be a freshman at Washington University in St. Louis next year, and I am excited to start a new adventure there.
This is my second year interning with Water Rocks!, and while I enjoyed a second season of counting middens and attending fairs with the Conservation Station, I also wanted to try something new: data analysis. I had already experienced collecting water samples in the field from lysimeters, and now I wanted to take it further and see the results of the project and finally the implications of the results and the effects that they could have.
In the most recent blog post, Getting Dirty and Getting Samples, Mary described how the water samples from lysimeters are collected. Where she left off, Jessica, another high school intern and my sister, and I come in.
We have been working on analyzing the lysimeter project data from 2014 and 2015. Lysimeters collect groundwater samples, which are sent to the lab and analyzed for nitrate. The Iowa Learning Farms team is comparing the amount of nitrate in the subsurface water for corn vs. soybeans, and single cover crop vs. a cover crop mixture vs. no cover crop.
There are five sites where the Iowa Learning Farms team has collected water quality data for three years now: ISU Research Farms at Lewis, McNay, Crawfordsville, Kanawha, and Nashua. Each site has 24 plots (and thus 24 lysimeters), with 12 plots each for corn and soybeans. Within each cropping system, there are three treatments: plots with no cover crops, plots with a single cover crop (oats before corn; rye before soybeans), and plots with a cover crop mixture (oats, hairy vetch, and radish before corn; and rye, rapeseed, and radish before soybeans).
Data are collected about eleven times per year from each lysimeter (from approximately April through November, as the weather allows). This all adds up to a lot of data to analyze–almost 800 samples per year!
Jessica and I compared the lysimeter results from one plot with itself throughout the year, from one plot with a certain treatment to other plots with the same treatment, as well as comparisons between treatments. We also looked at precipitation data and the volumetric water content at 12 and 24 inches deep in the soil, measured at each site (from Iowa State Agclimate Automated Weather stations). We lined up the data from the lysimeters with the precipitation and volumetric water content data at each site to look for patterns and correlations.
Analyzing data was a fun and challenging experience. It was fun to figure out how what would be interesting to look at and compare, and how to best present the data. As we worked through the data, we kept coming up with more ideas for what to do with it and what graphs to make.
Our preliminary results indicate a positive water quality benefit comes from using a cereal rye cover crop ahead of soybeans. Cover crop mixtures can also help, but so far, across multiple sites, we have found that having a single species cover crop of rye ahead of soybeans is the most effective treatment for having a low amount of nitrates leaving the field. Preliminary results from Kanawha are shown below as an example. Since I do not know what a statistical difference between measurements would be, I cannot claim any definite results of the data yet.
The water quality trends were less clear with corn. While a single species cover crop (oats) is also the most effective for corn, it is far less effective than rye is for soybeans. The cover crops used ahead of corn (oats, hairy vetch, and radish) all either die off over the winter OR yield very little spring growth. The biggest difference in the soybeans was the use of cereal rye and its winter hardiness — the spring cover crop growth made a huge difference in terms of water quality benefits! As the rye on the soybean plots has more to time grow in the spring, it uptakes more nitrate. Corn is planted earlier in the season, so if rye were growing prior to corn, it would have to be terminated earlier, yielding less benefit for the nitrate uptake by the cover crop.
Ideally, the amount of nitrate leaving the field (represented by the water that a lysimeter collects) would be low. Nitrate is most useful on the farm field, as it is dangerous in high concentrations to humans and pollutes water. Depending on the final results of the data, this research could potentially be used to show how and which type of cover crops are most effective in holding the nitrate in place without letting it move into water sources.
This research and its results are important for water quality across the state of Iowa. The Iowa Nutrient Reduction Strategy aims to reduce nutrients in water coming from point sources, like wastewater treatment plants, and nonpoint sources, like farms. A high concentration of nutrients can cause hypoxia, a condition of an area of water that cannot support marine life because it does not have enough oxygen. Hypoxia is a problem in the Gulf of Mexico, and currently the states along the Mississippi River have (or are working to develop) nutrient reduction strategies to help solve this.
This research is made more relevant with the current lawsuit between Des Moines Water Works and three Iowa counties. The Des Moines Water Works uses the Raccoon River for their half million consumers, and they want the amount of nitrates coming from farms in the counties to decrease.
Farmers can make a huge impact on the amount of nitrate in water. I attended a meeting of the Ames City Council in the spring, and the Water and Pollution Control Administration presented to the Council. They could put $36 million into reducing nitrate leaving their facility, but there would be little overall effect. Since farms contribute 92% of the nitrogen load, while municipalities only contribute 8%, we need to consider how much focus there is on reducing the contribution from the point source pollution sources in the municipalities as well as on farms. The research that we are doing will hopefully help show farmers that cover crops are a great way to reduce the amount of nitrate leaving their fields, while also helping to build soil health and protect our soil from erosion.
Overall this internship has been very influential in what I am interested in. I am undecided on what I would like to major in at WashU, but I know that I would like to continue studying science and the environment, including taking a class on environmental science. I care about protecting the water, soil, and climate, and this internship has helped me to realize that.