The following is a summary of “Managing Spring Planted Cover Crops for Livestock Grazing under Dryland Conditions in the High Plains Region”, a fact sheet produced in collaboration with extension specialists and research scientists at K-State, Colorado State University, and University of Nebraska. The comprehensive publication details recommended practices for species selection, adjusting stocking rates, and grazing management. The entire fact sheet can be viewed and downloaded at https://www.bookstore.ksre.ksu.edu/pubs/MF3443.pdf.
Selection of Species
Determining what to plant can be a daunting task with all of the varied species available for use as cover crops. For Kansas and Nebraska producers, local Land Grant Universities and the Midwest Cover Crops Council have developed a decision tool to help select species based on specified goals. When cover crops are grazed, one needs to choose species that will not only benefit soil health but will also be palatable and safe as forage for livestock. Fortunately, many of the species currently recommended for use as cover crops are also good for forage production. Factors such as nutritive content and potential toxicities must be considered.
While a number of potential problems can occur with various forages, most can be managed. The most frequent problem is the accumulation of nitrates that is common with oats and brassicas but can occur in a variety of species under certain growing and management conditions. Prussic acid is another toxicity to beware of when grazing, particularly with sorghums, but these species are less common in spring planted mixtures. Refer to publications on nitrate (CSU or KSU fact sheets) and prussic acid (CSU or KSU fact sheets) toxicities for more information. For a more complete overview of forage crops with potential toxicities, please see the publication Grazing Management: Toxic Plants.
For spring planted cover crops, most, if not all, of the species planted should be classified as cool-season in order to be able to plant early and take advantage of winter and early spring moisture. Species that fall into this category include the small grains (e.g. wheat, barley, oats, triticale, and cereal rye), brassicas (e.g. turnip, rapeseed/canola, and radish), and legumes (e.g. field/winter peas, winter lentils, vetch, and sweetclover).
Complex mixtures of 6 or more species, often referred to as “cocktails,” are commonly recommended. The benefits of cocktails relative to single species or simple mixtures of 2 to 4 species depend on your specific management goals. Competitive cool-season grass species tend to be the highest biomass producers, which can optimize weed control and forage production. Mixtures are often used for benefits other than biomass production, such as providing nitrogen fixation by including legumes or soil pest suppression by including brassicas. From a grazing perspective, mixtures can produce forage with a range of palatability that can provide benefits and limitations.
Variability in Forage Production
Forage productivity will vary from year-to-year under dryland conditions, which makes this one of the biggest challenges facing producers that graze cover crops in the High Plains Region because stocking rates will need to be adjusted annually.
Producers have several options to manage this variability in forage production. A flexible herd size where animals can be added or subtracted based on a given year’s productivity is the ideal situation. If it is difficult to adjust herd size, then the number of days a field can be grazed will have to be shortened or lengthened to achieve residue goals. In reality, expect to graze spring planted cover crops for about 30 days in most years. This resource should be viewed as supplemental forage during the late spring and early summer to help relieve dependence on other forage resources such as native rangeland and baled hay. In most years, native pasture growth is sufficient for turn-out when cool-season cover crops near maturity. High stocking rates can help suppress stem elongation and heading, but producers need to be careful to not overgraze and leave sufficient residue for soil health benefits.
As a final note, in years with minimal precipitation and forage productivity (i.e. ~1,000 lbs/ac or less), the best choice might be to not graze at all if your primary goal is soil protection. Ideally, you want to maintain a minimum of 30% ground cover, and approximately 1,000 lbs/ac is needed to achieve that goal.
When it comes to managing grazing of cover crops, numerous options can be considered. The ultimate strategy that is chosen will be influenced by your overarching goal(s) for the cover crop. Cover crops are generally grown for more reasons than just achieving high levels of harvest efficiency (i.e. percent utilization of available forage) as you would if this were a dedicated forage crop. You want to leave enough residue behind to maintain most of the benefits associated with planting cover crops (Figure 1).
Figure 1. Example of grazing and trampling impacts when predominantly cool-season grain cover crops are grazed during the heading stage. Regrowth is minimal and utilization is light (<30%) at this point, but trampling has left more than the target minimum of 30% ground cover.
Grazing management options include:
Once you have settled on a method of grazing, the next decision you need to make is when to start grazing your cover crop. If you are grazing steers and heifers and your goal is to achieve a given level of weight gain, then you need to start early to take advantage of high forage quality. The mixes we have been using for spring planted cover crops tend to be dominated by cool-season cereal grains like oats and barley. Once these species achieve 6 to 8 inches of growth, you should think seriously about starting to graze (Figure 2). Alternatively, some producers are more concerned about meeting their biomass goals for soil health and delay the start of grazing until plants are fairly mature.
Figure 2. The above photo illustrates the proper time to start grazing (6 to 8 inches).
Determining Stocking Rates
Several key pieces of information are needed to estimate a stocking rate. The first is an estimate of the forage yield your field will produce during the period it will be grazed on a dry matter basis. How much forage will be consumed each day will depend on animal body weight and forage quality. For green and growing forages, intake will run from 2.5 to 3% of body weight on a dry matter basis. Another key input is the percent utilization desired. In dryland systems, 30% is a conservative starting point unless it appears to be an excellent moisture year with above average yields. Calculations can be made to estimate days of grazing for a given number of animals or the number of animals for a set grazing period. A Carrying Capacity Calculator is also available to help with these calculations. Example calculations to determine stocking rates are detailed in the full publication linked in the first paragraph of this article.
An example timeline is shown below with suggested planting, start grazing, and end grazing dates for spring planted cover crops. This timeline will allow cover crops to effectively utilize winter and spring moisture to produce the highest yields possible under dryland conditions while providing livestock with high quality forage.
Joe Brummer, Extension Forage Specialist, Colorado State University
Sandy Johnson, Extension Beef Specialist, Northwest Research-Extension Center
Augustine Obour, K-State Agricultural Research Center, Hays
Kat Caswell, Extension Educator, University of Nebraska
Angie Moore, Research Associate, Colorado State University
John Holman, Cropping Systems Agronomist, Southwest Research-Extension Center
Meagan Schipanski, Cropping Systems, Colorado State University
Keith Harmoney, K-State Agricultural Research Center, Hays