Figure 1. Attributes of forage cover crops differ widely, depending on the species being grown and grazed. These differences should be considered when deciding whether to integrate cover crops into a grazing system and if so, what plant species to use. (Photo by Roger Elmore)
Growth and production patterns vary among the many species used for forage cover crops. Growth of forage cover crops, which are planted following grain crops production, is influenced by:
the amount of light penetration (affected by residue amount),
water availability (including soil moisture plus precipitation),
appropriate growth temperature (planting date and accumulated growing degree days), and
soil fertility (residual N and availability of nutrients). Based on the grain crop they follow, any combination of these conditions can limit forage cover crop growth.
Ease of forage cover crop establishment ranges from very easy, following wheat and hybrid seed corn production, to challenging following corn grain production. The probability of success is very high following wheat, hybrid seed corn, and corn silage production, but only moderately successful following soybean production. The relative ease and success rate is clearly related to planting date of the forage cover crop.
Variable Nutritional Value
Forage cover crops, including a variety of warm-season and cool-season grasses, legumes, and forbs, also differ in the quality of forage they provide. As a general rule, warm-season grasses have lower nutritional value than cool-season grasses and grasses have lower nutritional value than legumes. Brassicas and other broadleaf species and forbs often have quite high nutritional value. The grazing nutritional value for mixed forage cover crops depends greatly on
what plant species are included,
how much is produced by each species, and
what the animals select to eat.
Season of growth and plant maturity are important factors for determining nutritional value. For example, most forage cover crops have outstanding nutritional value during the fall. The exceptions are warm-season species, such as the early-planted sorghums or millets and some of the early-planted spring species such as oats or spring barley. All of these species will likely reach a reproductive stage of growth when planted in July immediately following wheat, so the nutritional quality is usually lower. The nutritional value of forage cover crops planted from mid-August through early September is high with total digestible nutrients (TDN) ranging from 70% to 80%. Crude protein (CP) will vary from 10% to 20% depending on the amount of nitrogen available for plant uptake.
Variable Animal Gain
Minimal data is available on beef gains from grazing forage cover crops. Most of the reported animal gains are based on observations or testimonials, rather than sound research. Therefore, the information may be limited to unique conditions and not reliable for widespread application.
Animals grazing forage cover crop mixtures that are mostly brassica, are reported to have lower gains than animals grazing other mixtures. Most of the differences in animal gain from grazing forage cover crops are caused by the differences in forage production and nutritional value.
However, there are other factors besides yield and quality that influence gain, such as rate of passage. For example, many brassicas have low dry matter, low fiber, and high soluble carbohydrates, which results in extremely high digestibility and nutritional value. Even though these characteristics are used to define high quality forage, the quality may be too high for ruminant animals. Producers who provide a dry forage like straw or hay free choice while grazing brassicas often report 0.5+ lb/day improvement over no additional forage.
Forage cover crops grazed during the spring can still have variable animal gains. However, these differences are more easily attributed to the maturity differences of the forage cover crops. As plants mature in the spring, the nutritional value of small grain forages declines as forage yield increases. When small grain forages are in the boot stage, total digestible nutrients will have decreased to 50% to 60% with crude protein around 8% to 12%.
Summary
There is limited information on seasonal forage cover crop production potential or animal gain for many forage cover crops. The available grazing performance data suggests that opportunities exist for improving the management of forage cover crops in many cropping systems. While there are many positives to incorporating forage cover crops into existing forage systems, growers should consider differences in production, nutritional value, and animal gain that exist.
Daren Redfearn, Nebraska Extension Forage and Crop Residue Specialist Jerry Volesky, Nebraska Extension Range and Forage Specialist Bruce Anderson, Nebraska Extension Forage Specialist
