By MATT HELMERS
If a picture is worth a thousand words, a demonstration has to be worth even more. Iowa Learning Farms has been using this concept for nearly 10 years with a Conservation Station fleet of trailers that house the Conservation Systems Rainfall Simulator.
Like many portable rainfall simulators out there, ILF’s first rainfall simulator had soil trays filled with disturbed soil. On each tray, we placed varied amounts of crop residue on top of the soil. An oscillating nozzle uniformly rained on each soil tray. This demonstrated how residue helps dissipate raindrop energy, reduces soil detachment by raindrops and shows how residue management impacts surface water runoff and erosion.
But this approach of using disturbed soils didn’t show the greater picture of how land management choices can impact soil structure. When using disturbed soil, it wasn’t possible to illustrate conservation practices such as cover crops, and since the depth of disturbed soil in the trays is often limited to 2 to 3 inches, the soils in the trays quickly became saturated.
Painting a clear picture
Due to these factors, we designed a better Conservation Systems Rainfall Simulator. We wanted to be able to vary rainfall intensity on each tray to illustrate how runoff and soil loss is impacted by different rainfall rates. Now each tray receives rain from an individual nozzle where the pressure can be varied to adjust rainfall intensity.
Next we integrated the use of undisturbed soils in each tray. To accomplish this, we designed two-part soil trays. The first tray, about 8 inches wide by 18 inches long and 6 inches deep, is open on the bottom and is pushed into the soil in the field, similar to a cookie cutter. The soil is cut on the bottom, and a second tray is attached onto the bottom of the first tray. The bottom tray illustrates the impacts of subsurface drainage on pathways of water flow.
With the new trays we can now cut soil samples from a variety of field conditions to demonstrate how management can impact water flow through changes in soil structure. For example, we can compare soil from tilled and no-till fields to show how no-till systems improve soil structure. While maintaining crop residue cover, the no-till system sees greater quantities of water moving into the soil, rather than over the surface as in a tilled system. By keeping the same undisturbed soil for multiple demonstrations, it also shows how, over time, surface seals develop on soils that lack crop residue cover. This seal limits water movement into the soil.
With trays of undisturbed soil, we can grow cover crops or take samples from fields with perennial vegetation. When it rains on the new soil trays, it shows how land management choices can impact water runoff and soil erosion. Also, the deeper soil trays allow us to demonstrate some of the new technologies being used in urban areas, such as permeable pavers to minimize water runoff.
For more on the rainfall simulator, go to waterrocks.org and click on “Catch the Wave” and then “Conservation Station.” Here you can learn about the fleet, request a Conservation Station visit to your event, view the 2015 schedule and more. For information about Iowa Learning Farms, visit extension.iastate.edu/ilf.
Helmers is the Iowa Learning Farms program manager.
This article published in the April, 2015 edition of WALLACES FARMER.
All rights reserved. Copyright Farm Progress Cos. 2015.
Field Conservation Maintenance/Practices