Consider the unique biology of flood-irrigated hay meadows
Flood-irrigated hay meadows are often an overlooked component of many ranches. Understandably, of all the pressing decisions to be made on the ranch, it’s easy for meadows to take the managerial back seat.
In many ways, this may be why meadows behave the way they do. By repeating the same management in the same environment decade after decade, meadows have uniquely adapted to the conditions placed upon them.
However, this relative consistency can be problematic when meadow performance no longer matches ranch goals.
After fielding continued questions from meadow hay producers in Wyoming and Colorado, University of Wyoming (UW) Extension was fortunate to receive funding from the U.S. Department of Agriculture’s (USDA) National Institute of Food and Agriculture in 2021 to undergo a four-year research project examining meadow productivity.
Instead of simply readdressing basic agronomic practices like fertilizer rates, researchers set out to better understand the hidden biological factors which drive and limit meadow hay production.
Research findings
In the end, what they found wasn’t surprising – there is no silver bullet for flood-irrigated meadow hay production. However, researchers did reaffirm some critical factors that should always be considered when managing meadows.
For one, meadows are cold. All of the meadows researched throughout Wyoming and Colorado were above 7,000 feet in elevation and had an average frost-free period ranging from 42 to 107 days.
This short, cool growing season clearly limits productive potential, making it important to set realistic production goals.
Mountain meadows simply can’t consistently produce four to six ton-per-acre hay crops like two-cut systems at lower elevations.
Productive capacity can also vary widely among individual meadows depending on water availability, forage species and fertilizer programs. Therefore, when planning for ranch hay needs, referring to a long-term average yield is important to reduce frustration from perceived poor performance and excess spending on unnecessary inputs.
Secondly, meadows are wet. Because of the limited growing season and yield potential, it often doesn’t make sense to spend large amounts of money to improve irrigation infrastructure.
In turn, flood irrigation systems predominate. But when taking a step back, one may realize this clearly impacts meadow plants and soil.
Would someone expect their garden to perform well under three inches of water for 30 to 60-plus days? In the same way, many desirable forage species simply cannot tolerate the lack of soil oxygen in a continually wet meadow and are easily outcompeted by plants that can.
For example, results from this study confirmed the common predominance of creeping meadow foxtail in meadows because of its water-loving nature and responsiveness to fertilizer. Under typical meadow management conditions, creeping meadow foxtail grows taller and shades out shorter clovers and native plants when nitrogen (N) is highly available in ponded soils.
This is only one example of the natural adaptation of meadows to producers’ management decisions, and just as the plant community responds to management, so does the soil.
Like plants, soil microorganisms are largely more active when soils are warm and have plenty of oxygen, and their ability to decompose dead plant material and manure is reduced during the wet irrigation season and also during the long, cold winter. This leaves only a short period of time for optimum microbial nutrient cycling in meadow soils.
Researchers investigated the interactions between soil microorganisms – primarily fungi and bacteria – and their influence on nutrient cycling in the distinctive heavy thatch present at the surface of most meadows.
They found fertilized meadow soils had higher amounts of microorganisms than unfertilized meadows and rangeland soils, suggesting nutrient inputs stimulate microbial growth.
This higher microbial biomass in the fertilized meadows, however, was dominated by bacteria, while the unfertilized meadows were dominated by fungi. In general, having higher amounts of fungi than bacteria, as was found in unfertilized meadows, can support better soil stability, greater carbon sequestration and improved long-term nutrient retention.
Impact of flood irrigation
The impact of something as simple as flood irrigation on soil microorganisms can easily go unnoticed, but it plays an intricate role in overall productivity of a meadow. If microorganisms are inactive during the growing season, then their ability to release fertilizer nutrients, like N bound in the thatch layer, is limited.
In looking more closely at nutrient release from meadows, researchers noticed soil microorganisms release N from the soil most rapidly during haying season when the soil is well aerated, warm and soil microbial biomass is highest.
Conversely, N release is slowest during the latter half of the irrigation season when the soil is ponded and depleted of oxygen.
This observation confirmed many recommendations given by universities for improved meadow management in the 1960s and 1970s, namely, the importance of moving irrigation water frequently to keep the soil from getting waterlogged.
Looking at the big picture, this all makes sense. Growing hay at high elevation narrows the productive season, and inefficient irrigation further slows overall biological activity.
Although researchers investigated other management tactics to stimulate the soil, such as tillage, heavy grazing and biofertilizer application, they found many ineffective in overcoming the challenges imposed by important underlying factors.
Researchers also realized lofty improvements in meadow productive capacity must greatly alter the soil environment and are therefore not likely to be economically feasible in a short growing season at high elevation.
Alternatively, recognizing the inherent qualities of meadows and optimizing inputs to fit an operation may be equally viable.
Daniel Adamson is a soil conservation Extension specialist at Oklahoma State University; Rael Otuya is a graduate student in soil science at UW and Linda van Diepen is an associate professor of soil ecology at UW. Any opinions, findings, conclusions or recommendations expressed in this publication are those of the authors and should not be construed to represent any official U.S. Department of Agriculture or U.S. government determination or policy.
