Cover crops have been around for millennia. Many ancient civilizations, including those in Greece, Rome, and China, recognized that cover crops and crop rotations with legumes could improve soil fertility and prevent erosion.
In the U.S., cover crops were common until the 1950s. Nutrients were often limited, and leguminous cover crops were one of the primary ways to add nitrogen to the soil. Cover crops were also used to help prevent erosion and suppress weed growth. In addition, cover crops improved the soil structure and organic matter content of the soil.
Before the development of synthetic fertilizers, cover crops and crop rotations were critical components of maintaining soil health and a productive cropping system. The development of synthetic fertilizers, partnered with the advent of the Green Revolution in the late 1950s, shifted the focus toward monoculture farming and away from crop rotations. This ultimately led to a decline in cover crop use.
We are now beginning to realize that the organic matter content of the soil and soil health often decline when only synthetic fertilizers are used. Cover crops can address some of these limitations.
The value of a cover
Cover crops offer numerous benefits such as reducing runoff, preventing erosion, increasing soil organic carbon (SOC) content, and contributing organic matter to the soil. By improving the water and nutrient holding capacity of the soil, cover crops can help make plants more resilient, which will help improve yields. Additionally, cover crops can be a good forage source for livestock.
The use of cover crops in crop production has also been shown to reduce nutrient leaching. By boosting the water and nutrient holding capacity of the soil, more nutrients can be retained, giving plants a chance to intercept and utilize the nutrients. The additional roots and microbes present from a cover crop can also capture nutrients, retain them, and then release them later. Cover crops that are mixtures of several plant types will support multiple types of microbes, which can further help reduce nutrient loss. Reducing nutrient loss helps improve yields, reduce fertilizer costs, and minimize off-target effects to the environment.
Consider the elements
Recent Utah State University surveys reported that although nearly 50% of Utah producers think cover crops can be beneficial, and they may use them at some point in the future, current adoption rates are modest. Much of that is likely due to skepticism as to whether or not cover crops will actually work in Utah. A relatively short growing season, limited water quantities, timing of when water is available, and a lack of local studies showing applicability in the Intermountain West create uncertainties.
Most of the information on cover crops comes from other regions in the U.S. where there is more precipitation, a longer growing season, and different cropping systems than what is found in Utah. A common crop rotation utilized in Utah is alfalfa for five to seven years, followed by corn silage, and then wheat before the new alfalfa crop is planted. This crop rotation returns little residue to the soil, so the addition of cover crops would be beneficial.
One of the biggest issues in the Intermountain West is the lack of water. Rainfall is limited with most precipitation falling during the winter months. Our irrigation water primarily comes from snow melt that is captured in reservoirs. Canal companies release water during the main portion of the growing season, but irrigation water is often not available early in the spring and much of the fall. Both the relatively short growing season and the limited water availability in the fall pose a problem when trying to establish cover crops.
One way to address some of these limitations is to interseed the cover crop while the corn is at the V3 to V5 stage. The goal is to minimize the ability of the cover crop to negatively impact corn establishment and growth while also getting the cover crop established before the corn canopies over and blocks direct sunlight. By interseeding early in the season, the cover crop is established when water is available, and it gives the cover crop a jump start for growth once the corn crop is harvested.
The biggest drawback to interseeding at the V3 to V5 stage is that there is a narrow window for getting the cover crop planted. Interseeding past the V5 stage can result in severe damage to the corn crop.
Select cover crops for interseeding based on their ability to grow underneath a corn canopy. In Utah, we are typically using a cover crop that is a mixture of a cereal crop or annual ryegrass, a vetch or legume, and a brassica such as radish. There is typically no yield loss when a cover crop is interseeded.
Aiming to minimize losses
Nitrogen (N) is of greatest concern when it comes to nutrient losses from fertilizer and manure, although phosphorus can also create problems. Nutrients lost through leaching and volatilization are an economic loss for producers and an environmental concern.
Nutrients that get into our surface water sources often result in eutrophication and fish kills. Harmful algal blooms (HABs) are becoming a bigger issue, impacting recreational areas, human health, pets, and livestock.
Nutrient leaching of fertilizers can contribute to groundwater contamination. More and more wells now exceed the U.S. drinking water standard of 10 parts per million (ppm) nitrate-N. High nitrates in drinking water can impact human and animal health, resulting in blue baby syndrome and spontaneous livestock abortions. Even more concerning is the strong correlation between high nitrate levels in the drinking water and the occurrence of multiple pediatric cancers, including brain and central nervous system cancers.
To improve the adoption of soil health practices in Utah, a study funded by a Natural Resource Conservation Service (NRCS) Conservation Innovation Grant (CIG) is underway. This statewide study examines soil health at 17 farms that are incorporating various soil health practices and comparing them to the standard practices used on their farms.
At two of the locations in northern Utah, mini zero-tension lysimeters (12-inch diameter) were installed below the root zone to collect leachate (see photo). PEX tubing was buried from the lysimeter to an access point at the edge of the field. Planting and tillage can take place over the lysimeters. Both farms have a sandy loam soil, apply manure, and are incorporating cover crops as their soil health treatment. The water table is only 3 to 5 feet below the soil surface.
Leachate is collected bi-weekly throughout the growing season, and as late as possible in the winter. Leachate samples are analyzed for available nitrogen and dissolved phosphorus. Deep soil cores are also being collected to a depth of 5 feet and will be analyzed for available nitrogen and phosphorus. Other scientists are examining various soil health metrics, such as bulk density, soil carbon tests, and water infiltration.
In 2023, both farms, which we will refer to as Farm GS and Farm JC, planted silage corn and interseeded a cover crop (a rye, vetch, and brassica mix) at the V5 stage. Due to the short growing season, cover crop establishment early in the season is needed to get adequate cover crop growth in the fall. Both Farm GS and Farm JC exhibited similar results, producing less leachate with a lower nitrate concentration under the cover crop. The total nitrate lost due to leaching under the cover crop treatment was about half that compared to the conventional (no cover crop) treatment for both farms (Figure 1).
In 2024, Farm GS began transitioning to alfalfa. Oats were planted in the spring and terminated for a late summer or early fall alfalfa planting. No cover crop was planted into the oats as there was plenty of volunteer cover crop. A three-way grass mixture will be interseeded into alfalfa in 2025 for the soil health treatment. Nutrient leaching was less overall than in 2023, but the results were similar in that leaching was reduced significantly (about 40%) when a cover crop was used (Figure 2). Farm JC planted silage corn in 2024 but missed the window for getting the cover crop planted so there was no cover crop treatment, and no differences were found between the two treatments.
On both farms, the leachate (on average) exceeded the drinking water standard for nitrate concentration even with the cover crop. The application of manure in the spring on a sandy loam soil likely contributed to this result.
In both 2023 and 2024, when a cover crop was utilized, the total nitrate lost due to leaching was approximately half that of the conventional (no cover crop) treatment with no reduction in yield. This indicates that the cover crop was able to use excess nitrate and possibly improve fertilizer nitrogen use efficiency in silage corn production, without harming silage corn yield.
This study will continue for three more years. The goal is to verify and demonstrate practices that improve soil health and minimize environmental impacts.
This article appeared in the August 2025 issue of Journal of Nutrient Management on page 14.
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