Community Agriculture Alliance: Graduate assistant studies how to access nutrients locked in irrigated meadow’s thatch layer |

Community Agriculture Alliance: Graduate assistant studies how to access nutrients locked in irrigated meadow’s thatch layer

Greg Peterson
For Steamboat Pilot & Today

Irrigated meadows are a unique forage system that dominates the high elevations of Colorado. However, research on high-elevation irrigated meadows is hard to come by, and these types of agricultural operations provide forage and many ecosystem services because of how they are irrigated and managed. One aspect of these systems that gets little attention is the thatch, sod, or organic layer.

The thatch layer is not only high in organic matter, but high in organic nitrogen. Years of flooding and cold temperatures slow down the rate of decomposition, leaving a significant amount of nitrogen locked up in the soil. Different studies have found anywhere from 1 to 2.2 tons of nitrogen per acre in the thatch layer. 

Considering the high costs of nitrogen fertilizer, this is a significant source of nutrients. More importantly, how do we utilize this source of nitrogen? Right now, Daniel Adamson, a graduate research assistant at the University of Wyoming, is working with four ranches in the Laramie Valley, Wyoming and North Park Valley, Colorado to answer this question. All ranches are above 6,500 feet in elevation and use flood irrigation, similar to conditions in the Yampa Valley.

Adamson and staff from UW have confirmed not only the amount of nitrogen build-up in irrigated meadows, but that the majority of that nitrogen is contained in the O-horizon: the first 2 inches of the soil profile.

This diagram compares the amount and placement of nitrogen (N) between rangeland and a fertilized and irrigated meadow.
Community Agriculture Alliance/Courtesy image

Short of plowing up these perennial grass fields, what can we do to break up the sod layer and access all the available nitrogen? Adamson and his team will be looking at a variety of practices that will hopefully improve nitrogen availability.

This year, they are examining the impacts of light mechanical disturbance, running a ripper through the fields. Livestock disturbance is another method to hopefully disturb locked-up organic matter in the soil. But determining the optimum amount of time cattle spend on the field will be one of future research.

Greg Peterson is the Executive Director for the Colorado Ag Water Alliance.

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