Extend the Grazing Season With Cover Crops

Introduction

(Courtesy: USDA NRCS South Dakota)

With hay prices still high, extending the grazing season is key! Grazing cover crops in the fall and spring can extend the grazing season and reduce feed costs. For fall/winter grazing, selecting cover crops that are winter-killed in South Dakota environments are preferred; whereas, for spring grazing, species that can overwinter are ideal. Selection of cover crop species is dependent on time of planting. Growing after small grain harvest (usually late July through early August) for fall/winter grazing provides an ample seasonal window to select species from a wide range. Common cover crop species used after small grains are brassicas (radish, turnip, rapeseed), grasses (oat, barley, millet, sorghum sudangrass) and legumes (vetch, chickpea, sun hemp, lentil, pea). The overwintering species generally used in South Dakota are winter cereals, such as winter rye, winter triticale, and winter wheat. In some cases, these winter cereals (especially rye) can be grazed both in the fall and spring depending on weather, grazing management, and regrowth potential.

Considerations Before Planting

Turnips and radishes are common brassicas grown in the Midwest; with adequate moisture, they produce high-quality forage ranging from 15 to 20% crude protein and 60 to 70% TDN. However, high moisture content in these species can limit dry matter consumption and affect performance (Figure 1). The roots, stems, and leaves of the brassicas are all palatable to cattle. When grazing turnips or radishes, cattle should have access to lower-quality hay to provide them with adequate amounts of fiber, which will help prevent bloat. Due to high sulfur content, cattle may not prefer brassicas right away and may need acclimation to grazing.

Figure 1. SDSU Southeast Research Farm

Planting a cover crop mixture creates selection for cattle as well as greater biological activity below ground, increased ground cover, and improved nutrient cycling, all contributing to building up soil health. Planting timing is a factor to consider as well. Warm-season cover crop species should ideally be planted anytime during the early-to-mid summer, but ideally no later than the first week of August. Cool-season cover crops should be planted approximately the third week of July, as average daily temperature tends to decrease due to lower nighttime temperatures at this time. Following small grain cash crop harvest, mixtures with both warm and cool-season species may thrive, even if the planting window is not ideal for both; however, it’s important to note that warm-season covers planted late in the season may not have adequate growth prior to any early frost.

Risks to Consider

Some species of cover crops have potential to be toxic to cattle. Common toxicities with cover crops include prussic acid, nitrates, and sulfur. Forage sorghum, sudangrass, and sorghum hybrids may experience prussic acid build-up and release in the leaves and stems following a frost, as they are very susceptible to cold temperatures.¹ Generally, it is recommended to keep cattle out of fields planted to mixes that contain a higher proportion of these grasses for about a week immediately following a frost event to let the prussic acid dissipate. In addition, nitrates may accumulate in cereal grain forages (especially oats), sorghum, sudangrass, and corn, dependent upon soil fertility management and environmental conditions. Accumulation is typically associated with drought stress, with greater concentration on lower plant parts. Forage tests are important to check prussic acid and nitrate levels, as well as forage quality. See Table 1 for cover crop options for grazing.