Infiltration + Appreciation

Hi there, my name is Amanda Marlin and I am a senior in Agricultural Engineering with a Land and Water emphasis here at Iowa State. I grew up in the country outside of the small town of Melcher-Dallas, Iowa. Saying I was a girl with a passion for the outdoors would be putting it lightly! I loved being outside and took any chance I could get to explore the timber out back or go check out the creek and try to catch some tadpoles with my brothers. I was what they would call a “tomboy” — a girl who wasn’t afraid to get her hands dirty. Getting my hands dirty is just what I have done while being an intern for Water Rocks! and the Iowa Learning Farms. I’m also involved with several different research projects with the ISU Ag Water Management team. I will explain one of my recent research projects that I was involved with so you can get a small glimpse of the type of work we do!

MeetTheInterns-Amanda

The project we have been currently working on is called Science-based Trials of Row Crops Integrated with Prairie Strips (native perennials), or the STRIPS project for short. The first prairie strips were planted in 2007 as Phase 1 of the project, and monitoring has showed that a 10% conversion to prairie strips from row crop can reduce soil loss by 90%, nitrogen runoff by 85%, phosphorus runoff by 90%, and 40% less runoff volume overall. It is a relatively inexpensive conservation practice with multiple, measurable benefits: wildlife habitat, bird habitat/food, pollinator habitat/food, beneficial insect refuge, reduced runoff, reduced nutrient concentration in runoff and groundwater, and reduced sediment loss from the field.

In Phase 2 of the project, implementation of prairie strips at research farms in Iowa as well as by private landowners began. Currently there are five paired comparison sites with flumes and groundwater wells to compare within the same field the effect of having strips present. Paired comparison sites ensure very similar slopes, soil types, and weather, allowing for direct comparison between treatments.

In the Field…
Traveling with my research team to the Iowa State University Armstrong Research Farm in Southwest Iowa last week, we spent long days in the field working with infiltrometers. An infiltrometer is a device used to measure the rate of water infiltration into the soil. Using a Cornell infiltrometer, we had 24 sites to collect data from that were either in prairie strips or a no-till field planted in soybeans, and four different soil types.

To begin, we would use GPS to find our location and then find a good area with no cracks in the soil so as to get accurate infiltration results. Using a 25 lb weight, we would pound in the ring with an impact-absorbing hammer so that the ring was about 5 cm in the ground. Making sure the hole faced downslope and the bottom of that hole was right at the surface, we also had to level the ring. Next we would place our outflow tube in the surface runoff hole to determine where to dig a hole to place our beaker. After digging the hole for the beaker, it was time to fill and calibrate the infiltrometer.

Infiltrometers-01-03Infiltration Preparation …

 

  1. Leveling the ring of the infiltrometer.
  2. Equipment setup before the infiltrometer is placed on top.
  3. Filling the infiltrometer.

The goal was to get the infiltrometer to rain at about 0.5 cm/min and then seal the air entry tube to stop the rainfall before placing it on the ring. Once the capillary tubes on the bottom of the infiltrometer stopped raining, then it could be placed on the ring and the height of the water in the infiltrometer recorded. From here the air entry tube was released and the stopwatch started.

The infiltrometer began to rain and the next step was to watch for initial runoff into the beaker.

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Intern Amanda Marlin waiting for initial runoff in the field.

Time and height of the water were recorded at initial runoff and from there, every three minutes the height of the water in the infiltrometer was recorded while simultaneously switching beakers to record the volume of water through runoff.

Infiltrometers-05

Intern Nathan Waskel recording the time and water level after initial runoff.

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Nathan finding his volume of water three minutes after initial runoff.

 

The goal was to keep the 0.5 cm/min infiltration rate and then watch for steady-state runoff. This could happen after anywhere from 15-60 min of infiltration to sometimes even longer than an hour. It was interesting to see the difference in runoff between the prairie strips and the no-till field planted in soybeans. The prairie strips clearly had better infiltration compared to the crop fields, and that’s what was found in Phase 1 of the project, as well. Overall the data collection with the infiltrometers went well and is now being put altogether into one spreadsheet to compare each soil type and where it is located.

Working with the infiltrometers will give us a better idea of how long it takes for the different types of soil and soil locations to infiltrate. Although we have gathered the data, we still have to take into consideration the many other factors that affect the infiltration rate such as the soil structure, the condition of the sediment surface, the chemical and physical nature of the soil, the atmospheric pressure, and biological activity in the soil. Taking all of these into consideration, these infiltrometers are used for comparative data and not specific values.

So some night when you are at home enjoying a rainstorm, just think where all that rainwater is going and what is happening to our soil. Is it infiltrating into the soil or is it running off into our lakes and rivers? These are things I would have never thought of when I was younger, but have now come to see that it is a big part of our environment and how our land and water interact.

Amanda Marlin