Lost in the Corn: The Search for Lysimeters

Today’s guest blog post was provided by summer student intern Laura Lacquement. A native Iowan, Laura grew up south of Des Moines, and went to school at Martensdale-St. Mary’s. She started her college career at Valparaiso University, and later transferred to ISU, where she is now a senior studying Environmental Science.  

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I enjoy travelling across the State of Iowa with Water Rocks! and Iowa Learning Farms. The location and events vary, while the field work remains consistent. One of the projects I’ve helped with all summer long is ILF’s cover crop mixtures project. Each week we travel to three of Iowa State University’s research farms to collect water samples from lysimeters located in plots of corn and soybeans.  Each block of plots contains 12 lysimeters placed between rows of corn or soybeans.

Lysimeters measure the movement or storage of water in the ground.  The lysimeters that the ILF team uses are composed of a tube two inches in diameter and two feet (24”) deep.  The bottom of the tube is composed of a porous ceramic cup that allows the movement of water into the lysimeter from the soil around it. Using a vacuum pump, we create suction inside the tube that pulls water inside.  Each week, we extract the water by using a flask that is connected to the vacuum pump on one side and a straw connected to its lid and inserted into the tube to its full depth.  Using the pump and flask, we pull water from the lysimeter into a small bottle, where it will later be analyzed for the amount of nitrates present. Each lysimeter tube is installed so it’s flush with the ground. To protect the lysimeter, a four inch PVC drainage pipe plug and small pipe is placed above it.

Most of our plots are located close to each other, with the exception of the plots at the ISU Northern Research and Demonstration Farm in Kanawha, Iowa. Finding the lysimeters there can be quite an adventure! At the start of the internship, all we could see of corn and soybeans in our plots were little sprouts an inch tall.  In just a couple weeks, the corn grew past our knees to over our heads.  I not only watched this growth, but experienced it firsthand by struggling to carry our devices and tools over and through the corn and soybeans to each lysimeter.

On Friday, June 30, I traveled to Kanawha, Iowa, with Elizabeth to extract water samples from lysimeters there. As I mentioned, the plots here are not located right next to each other, but in completely different fields separated by a grass driveway.  After we collected samples from the soybeans, we entered the corn in search of our small buried lysimeters in the shoulder-height corn.  We walked inside each row looking for our lysimeters … for an hour or so. Our ILF plots happen to be in the middle of a much larger field, and the challenge is that there’s no easy way to flag or label the plots once the corn is this tall! We eventually ventured a bit south of our current location, where we recognized our plots and finally spotted a lysimeter only a short distance away. Small victories!

Friday, July 7, I returned to Kanawha with Kaleb to collect more samples. This time, I knew exactly where to go to find the plot, but not the precise location of the lysimeters. In just one week, the corn had grown from the height of my shoulders to the height of me. I could no longer see over the corn.  As I finished extracting each water sample, Kaleb would move to the next lysimeter.  He may be the tallest of us interns, yet I still could not see him over the corn.  To find him and the next lysimeter, I followed the sound of corn rustling and looked for his bright red shirt through the corn.  If we do not wear bright colored shirts, a game of Marco Polo may be necessary!

After these experiences, I’m now very confident where ILF’s plots at Kanawha are located, plus how to find the other lysimeters and interns in corn taller than me. Each time I take samples from the lysimeters, I have learned a little more about corn and soybean cropping systems, as well as water quality issues in Iowa!

Laura Lacquement

Research Rocks!

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.

MeetTheInterns-EmilyThis 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.

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The Rehmann sisters out and about with the Conservation Station — Emily is on the left and Jessica (who blogged earlier this summer) is on the right!

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!

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We had ten of these big spreadsheets, plus summary sheets, by the end of the process!

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.

Kanawha Preliminary ResultsThe 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.

IowaNutrientReductionStrategyThis 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.

Emily Rehmann