AMES, Iowa — Now you see them; now you don’t. Different from permanent gullies, ephemeral gullies, formed in fields by running water, are erased when a farmer tills the soil, but reappear when another significant rain event occurs.
Ephemeral gully erosion, known to be a significant cause of soil loss from agricultural fields, is the focus of a USDA National Integrated Water Quality Program project led by Richard Cruse, professor of agronomy at Iowa State University. The project uses research, extension and education with the goal to better control ephemeral gully erosion.
“The most important goal of the project is developing a means of estimating the ephemeral gully erosion component of soil loss on farm fields,” Cruse said.
Current soil erosion models can only estimate sheet and rill erosion, which occur in small channels that can only be seen up close, where water flows and moves off the surface in very thin layers. Unlike gully erosion, those types of erosion cause soil movement and not necessarily removal from fields.
Karl Gesch, an Iowa State graduate student in agronomy, is using new, stereo photographic techniques to measure ephemeral gullies in several farm fields, to validate a model that can be used to predict where ephemeral gullies will occur on a field and how much soil could erode as a result.
“Any soil that moves through gullies is gone; much of it has left the field,” Cruse said. “With the tools we have now, we can roughly estimate how much soil is moving from hill slopes to lower elevations on farm fields, but this new study will give us a much stronger handle on what is actually leaving the landscape.”
How important is it to get a handle on topsoil loss and to conserve it?
Global studies show that the world’s cropland is losing topsoil faster than new soil is forming, reducing cropland’s inherent fertility. Data collected by Iowa State Emeritus Professor Tom Fenton in the 1980s shows that as soils erode, topsoil is thinned; and as topsoil thins, crop yields decline.
Other reasons to keep topsoil on fields are the offsite damages it causes when it moves into water bodies as sediment. Sediment, organic matter and the farm nutrients it carries, such as phosphorus, harms water quality and aquatic life in streams, lakes and rivers. Flooding also is exacerbated by sediment.
“Sediment from agricultural fields is filling Iowa reservoirs, reducing their capacity to hold water. When it rains and you do get a particular volume flowing down a channel, it doesn’t have anywhere to go, so the water level is going to be higher and impart more damage,” Cruse said.
Cruse said Iowa crop fields also are losing their ability to hold water.
“To keep excess waters from overflowing the banks of rivers, it’s best if we can store it in this big sponge that is the topsoil in our crop fields. Every time we send a ton of sediment down the river from an acre of land, we are reducing the ability of the landscape to store water by about 75 gallons. Annually in Iowa, under the scenario of losing five tons of topsoil per acre, per year, that’s 300-400 gallons of water retention lost per acre, per year,” Cruse said.
To reduce soil loss from ephemeral gully erosion, project partner Agren Inc. is using new computer software to design soil conservation systems like grassed waterways in minutes, versus several days. The software will be used to target and plan conservation practices for ephemeral erosion control on fields throughout the selected project area — the South Fork watershed in portions of Hardin and Hamilton counties.
Seth Dabney, an agronomist and research leader with the USDA’s Agricultural Research Service National Sedimentation Laboratory, is working with Agren and Iowa State to develop the model to measure ephemeral gully erosion.
“Once we have the model verified, we can determine the highest priority sites for ephemeral erosion control practices, which areas are losing the most soil,” said Jamie Ridgely, Agren’s chief operating officer. “Using the software programs together, we can identify sites in which applying grassed waterways will lower soil loss the most. We will rank those. Then we’ll do an outreach campaign to landowners with land in the highest priority areas in the South Fork watershed. We can then design practices that will have the most control, given each selected landscape.”
“We need the Iowa State research data to get confidence that the model is working right. Fall 2014 is when we hope to be talking to landowners on sites that have the highest potential for gully erosion,” Ridgely added.
Project findings regarding ephemeral gully erosion will be combined with what is known about other types of erosion and soil conservation practices, to create instructional modules for use by high school agricultural teachers for training the next generation of farmers. After developing the curriculum it will be tested in the four school districts within the project watershed.
Thomas Paulsen, assistant professor of agricultural education and studies at Iowa State, is the principal investigator for this portion of the project.
“High school agricultural education programs are directly connected to the communities they serve. By educating students about erosion control practices, they can become positive agents of change in their local communities,” said Paulsen.
Lindsay Calvert, an Iowa State graduate student in agricultural education and studies, is assisting Paulsen with curriculum development. This includes the creation, distribution and results analysis of a teacher questionnaire to ensure their educational modules will be readily integrated into current agricultural curriculum at the high schools.
Other members on the team are Elena Polush, assistant professor of educational studies at Ball State University, and her assistant and graduate student, Jose Martinez, who are providing evaluation and feedback throughout the three-year project.