Today marks the end of my time as an intern in the Agroecology Lab. I have been fortunate enough to spend the entirety of my senior year working in the lab with Dani Weissman and the other graduate students, Cullen McAskill the wonderful lab technician, and my fellow interns. Through my various research experiences in the lab, I have learned so much about biogeochemical cycling processes that impact agriculture, the importance of agroecology to integrate ecological and social approaches to agriculture, and standard chemical analysis research practices.
This semester I focused my efforts on a long-term research study to understand different nutrients, like nitrogen and phosphorus, that are dissolved and bound to soil particles in water samples taken from various agricultural plots on the Eastern Shore. Nitrogen in this form is formally called “Dissolved Organic Nitrogen” (DON), while other forms of nitrogen often found in the soil include nitrate and nitrite, which are necessary for plant growth. The agroecology lab is investigating these different forms of nutrients because it is important to understand how changing environmental conditions may impact the future of agriculture. Rising sea levels, for example, is causing saltwater from the ocean to intrude into agricultural plots on the Eastern Shore. This alters the chemical and biological processes that take place in agricultural soils (Osburn, 2016; Weston, 2006). To understand how nutrient forms have been changing over time in response to saltwater intrusion, I conducted digestion experiments on water samples to specifically target dissolved organic nutrients. Essentially, the experiment required me to add various chemicals to the water samples (as shown in Figure 1) and then run them through an autoclave, which heats the samples up to extremely high temperatures. This breaks up any bonds between the nutrients and dissolved soil components to isolate the nutrients to be further analyzed.
The results of this experimental digestion process will provide important information on plant nutrient availability once they undergo a next step of further chemical analysis. It is a good feeling to be able to contribute to the research findings of the Agroecology Lab. I will sorely miss my time working there now that the semester has come to a close, but I will be forever grateful to all that I have learned and for how it has changed my perspectives of agroecology.
Osburn, Christopher L., Lauren T. Handsel, Benjamin L. Peierls, and Hans W. Paerl. 2016. “Predicting Sources of Dissolved Organic Nitrogen to an Estuary from an Agro-Urban Coastal Watershed.” Environmental Science & Technology, 50: 8473-8484.
Weston, Nathanial B., Ray E. Dixon, and Samantha B. Joyce. 2006. “Ramifications of increased salinity in tidal freshwater sediments: geochemistry and microbial pathways of organic matter mineralization. Journal of Geophysical Research, 111: G01009.
- By Alexis Boytim
I am Jonathan Moy, an undergraduate intern in the Agroecology lab. I work with Elizabeth de la Reguera, an MS student here, in two of her projects. Her work is largely on how saltwater intrusion in Maryland affects the carbon found in soil. We recently finished transferring four thousand switchgrass plants to UMD’s greenhouse. Later in the year, the lab will be planting the switchgrass along with other salt-tolerant plants in saltwater intruded agricultural plots to determine the carbon the plants imparted in the soil. The data from that experiment will be helpful in giving farmers in Maryland a well-supported reason to use salt-tolerant crops in their crop rotations. The project I am working on right now examines the aggregate distribution in saltwater intruded agricultural fields. Soil aggregates are important to the available nutrients to the soils . We are most closely looking at soil carbon—thus the title of this post. Carbonation the way most people use it usually refers to carbon dioxide reacting with a beverage to make it effervescent. While that doesn’t happen in our soils, carbon is still very interesting in soils! The method we are using uses a series of sieves to separate the soil carbon by availability [2,3]. Essentially, the smaller the aggregates are, the less available the carbon is to the plants’ roots . One of the pictures with this post shows Elizabeth displaying the second smallest sieve we use in this experiment. Fun fact: the picture also features the very first sample we processed for this experiment.
During spring break, I was given the opportunity to visit the sites that we are working on! You may not be able to tell from the picture (I’m the guy in blue), but I had a blast soil sampling. If you look really closely, you can see that I’m smiling. Those soils were the same soils that we are processing right now, so that is just one more thing to be excited about when processing my samples. Before that, I spent a lot of time in the Greenhouse seeding, thinning, and transferring switchgrass until we had four thousand switchgrass plants individually growing in deep planting plugs.
- By Jonathan Moy
Ontl, T.A. et al. (2013). Topographic and Soil Influences on Root Productivity of Three Bioenergy Cropping Systems. The New Phytologist, 199, 727-737. doi: 10.1111/nph.12302
Elliott, E.T. (1986). Aggregate Structure and Carbon, Nitrogen, and Phosphorus in Native and Cultivated Soils. Soil Science Society of America Journal. 50, 627-633.
Six, J. et al. (2000). Soil Structure and Organic Matter: I. Distribution of Aggregate-Size Classes and Aggregate-Associated Carbon. Soil Science Society of America. 64, 681-689.
It is 9AM on a cold Tuesday morning in west Tennessee, and I find myself in a two-meter-deep pit in the middle of a farm field. The water in the ponded pit reaches up past the knee of my waders, and I can feel that my feet are stuck in the mud underneath. I can’t feel my fingers, but still I persevere, focusing on the task at-hand of acquiring samples from each horizon of the soil profile in front of me before I must get back out. This is just the start of a regular practice day during the week of the National Collegiate Soils Contest.
Five minutes in the pit, five minutes out. Ten minutes in, ten minutes out. Five minutes in, five minutes out. All followed by a twenty-minute free-for-all. Much like any other contest, soil judging has clearly defined rules. At the start of the contest, competitors are given scorecards and taken to soil pits. Each individual competitor has an hour at each pit to fill out their scorecard describing the morphology of the soil in the pit: its horizonation, structure, color, texture, redox concentrations, and taxonomy, just to name a few of the described features. After each competitor has judged every pit, the scorecards are graded for accuracy based on data collected by the hosting university. The individuals are ranked based on the highest combined scores.
The soils of Tennessee offered us great challenge and created much confusion with the presence of many unfamiliar features, such as the elusive glossic horizon, the cryptic lamellae, and the enigmatic plinthite; however, none of these features baffled us quite like the mysterious fragipan. Fragipans make up the dense, brittle subsurface layers hypothesized to form under conditions of compaction, deformation, and contraction (Graveel, Tyler, Jones, & McFee, 2002). As root- and water-limiting layers, calling a horizon a fragipan makes all the difference in correctly determining such important features as effective soil depth, depth to seasonally high water table, and water retention as well as soil taxonomy. Essentially, scoring well in the contest depended on correctly identifying fragipans. This may be appropriate, for the presence of and depth to a fragipan has major land use implications. Fragipans are shown to limit crop growth, with a study of soybean crops demonstrating decreases in both root growth and crop yields as depth to a fragipan decreases (Graveel, Tyler, Jones, & McFee, 2002). This issue becomes even more pressing in areas of loess deposition. The wind-blown silt blanketing the surface in such regions is highly vulnerable to erosion, especially in agricultural fields without proper erosion protection protocols, so these fields are at risk of losing yields over time due to this effective decrease in depth to fragipans.
The contest concluded with an awards ceremony under the iconic Eiffel Tower of Paris, TN. We took home fourth place overall, coming home with a lovely plaque and a much greater understanding of the soils of Tennessee.
- By Jonathan Wiechecki
Graveel, J. G., Tyler, D. D., Jones, J. R., & McFee, W. W. (2002). Crop yield and rooting as affected by fragipan depth in loess soils in the southeast USA. Soil and Tillage Research.
Smalley, I. J., Bentley, S. P., & Markovic, S. B. (2016). Loess and fragipans: Development of polygonal-crack-network structures in fragipan horizons in loess ground. Quaternary International.
I’ve been working with Cullen this semester, and since Cullen works on pretty much everything in the lab, I’ve had the privilege of being exposed to many different lab activities. I’ve gotten to work with Dynacrush the soil grinder, help weigh and prepare soil samples for KCl extractions, and use SamplePoint software to look at land cover and plant species diversity in field sites on the Eastern Shore. SamplePoint is a manual image analysis program that is used to classify different land cover types on individual nadir images . For each photo taken of the test plots, I classified one hundred different sample pixels as bare soil, plant litter, or one of about fifteen different plant species. SamplePoint then uses the manually-entered sample data to extrapolate the land cover classifications to the rest of the image. Quantifiable land cover data, such as the percent area of a plot that is covered by one specific plant species, can be a useful metric when assessing the impact of saltwater intrusion on plant species diversity.
One of the most rewarding experiences I’ve had so far in the lab has been the hands-on soil sampling work that we did over spring break at “soils camp.” We sampled several field sites that were experiencing saltwater intrusion, and it was fascinating to personally witness the visible signs of saltwater intrusion’s effects on these agricultural fields. There are generally very clear boundaries between the brackish water ditch inhabited by phragmites reeds, the adjacent area inhabited by low-lying salt-tolerant species such as salt marsh hay, the zone of generally bare soil, and then the transition into the agricultural field. By analyzing soil samples from these test sites, we can assess the impact that saltwater incursion has on nutrient release, carbon dynamics, nitrogen content, aggregate structure, and other soil properties  . Soils camp was a wonderful way to spend time outdoors, get covered in mud, work together with inspiring and fun people from the lab, and understand where and how the Agroecology Lab obtains the soil samples that we process and analyze back in College Park.
- By Anna Collishaw
Hello! I work with Josh Gaimaro in Dr. Tully’s AgroEcoLab. Josh’s research focuses on the cover crop management for nutrient cycling. Cover crops are planted between rotations of cash crops. They provides various ecosystem services and improve soil quality. On the first day of my work in the lab, Josh provided me with a brief introduction to his research, in which I learned more about cover crops. It is widely accepted that the cover crops can improve the soil by retaining and later releasing nutrients. They also reduce soil compaction and prevent nitrogen leaching losses. However, different species of cover crops may differ in their function and efficacy, which requires further study . Josh’s research looks into this problem and investigates the services provided by different species and mixtures of cover crops, including rye and radish. One important function of a cover crop is to remove excess nitrogen from the last cash crop and release it to subsequent crops in the spring . Rye and radish have different physical traits, and will differ in their performance of this action. We believe, that their combination might work even better. This is important information for both US agriculture and the global food system because nitrogen loss is a severe problem. Cover crops can help ameliorate this problem by increasing the efficiency of soil nutrient usage and reducing the application of synthetic fertilizer. Thus, Josh is exploring the effectiveness of different combinations of cover crops on nitrogen cycling, and I am helping him with the nitrogen uptake measurements.
My primary work in the lab are grinding soil samples and preparing the crop samples for analysis. To determine the nitrogen uptake, we need to know the amount of nitrogen in the soil as well as in the crops. Last year, Josh collected soil samples several times during the growing season. I weigh the soil after it has been air-dried and I grind the soil into even particles. For both soils and plant materials, I wrap a small amount into a piece of foil, so that we can analyze carbon and nitrogen content. The fun thing about two projects is that the crops come from “ashes” is turned into ashes in the lab; the dust from soil is also crushed into dust. So, I call my research project, “Ashes to ashes dust to dust”.
Check out the recent article in The Atlantic focusing on our research into saltwater intrusion. This great article was researched and written by Virginia Gewin.
Last semester I visited Elizabeth de la Reguera’s study sites on the Eastern Shore of Maryland. We prepared and planted small research plots with switchgrass, barley and wheat. Elizabeth is studying the effects of saltwater intrusion on crop productivity and survival. Over winter break, I continued to work on this research by gathering data on how well the different plant species were growing in each plot. The AgroEcoLab manager, Cullen McAskill, gave me hundreds of pictures from the site, and I got to work! Cullen had placed a quadrat on the plots in the fall, so that we could determine the species of different plants within a grid. Imagine trying to count each plant individually in each plot! Instead, the quadrat is placed at each plot in random so that it isolates an area that can then be used to represent how much of that plant species is in that plot. My job was to take each picture individually with the quadrats and set a scale in which we would tell the program, SamplePoint, to count how many plants were within those quadrats. Gathering all this data will not only tell us what species is doing the best or worst in salty conditions, but it will also provide us with the information we need to improve any management techniques in the future.
-By Karla Rosales Lobos
On Tuesday, 9 Jan, the AgroEcoLab's work on saltwater intrusion was featured in Maryland Public Television's weekly show, Maryland Farm and Harvest.
Check out the full video here.
A few weeks ago, I visited the experiment that Elizabeth de la Reguera has established for her Master’s degree at the University of Maryland. The question for her experiment is, what is the effect of saltwater intrusion on the productivity and survival of different plant species? We travelled to Eastern Shore of Maryland to till her plots and plant switchgrass, barley, and wheat. We used rakes to till the plots because we did not want to till too deeply, which would degrade the soil. We only needed to ensure good seed-to-soil contact, to help the plants germinate and prevent them from being blown away by the wind (grass seeds are REALLY small). Then, each type of seed was assigned to one person to disperse on the plots. The purpose of this is to have some kind of uniformity when it came to the dispersion of the seeds. While we were there we took water samples from the lysimeters that Elizabeth had already installed. When we came back from field, I started to measured the porewater conductivity and pH. The soils and porewater have high electrical conductivity, which is likely due to the high levels of chloride and sulfate moving into the plots with saltwater.
- By Karla Rosales Lobos
Dr. Kate Tully
Kate is an Assistant Professor of Agroecology at the University of Maryland.
Dani is a PhD student in the AgroEcoLab and studies the effects of sea level rise on coastal farming communities and estuarine biogeochemistry.
Resham is a PhD student in the AgroEcoLab and studies how to improve water and nutrient use efficiency in cover crop systems.