Cover crops can provide benefits for soil health and crop production systems but they use moisture which can be limiting in lower rainfall areas such as western Kansas. Post-wheat planted cover crops offer a potentially longer and more flexible grazing period than spring planted cover crops within wheat-based dryland cropping systems. However, low available soil moisture and variable weather patterns at this time of year can make cover crop establishment and productivity highly variable. In addition, concerns regarding diminishing good wheat stubble, managing volunteer wheat to reduce disease transmission, and controlling weeds need to be considered.
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. As an example of yield variability across years, Figure 1 presents 7 years of forage sorghum yields at the Southwest Research-Extension Center (SWREC) near Garden City, KS with long-term average annual precipitation of 19 inches. Forage sorghum planted after wheat produced an average of 5600 lbs DM/acre which was 75% of the full season yield and ranged from 1130 to 8900 lbs DM/acre over a 7-year period (Figure 1).
Based on a 2-year on-farm study conducted in western Kansas, eastern Colorado, and southwestern Nebraska, forage yields of a cover crop mixture ranged from 500 lbs/acre up to 2,300 lbs DM/acre (Table 1). The low DM yield was due to the type of cover crop mixture producers selected. Growing a single species of warm season grass such as forage sorghum would have resulted in increased yield, but cool-season species were included in the mixture to enable growth over winter. At some locations, regrowth was documented before spring termination but not in an amount sufficient for grazing. Earlier planting dates were associated with production of more biomass. These results would suggest growing either a warm season mix planted as soon as possible after winter wheat or delaying planting until the fall and planting a cool-season mixture. The effect of the east-west precipitation, elevation, and evapotranspiration gradient within the region was also evident as the 2 farms that were in the drier part of the region (i.e. eastern Colorado) produced less than the Oberlin, KS, location farther to the east. Approximately 50% of the time, producers determined grazing was not possible either due to lack of growth or wet soil conditions. If grazing sorghums be mindful of potential prussic acid in new growth or in the fall around frost events.
Table 1. Examples of dryland cover crop planting dates, grazing start and end dates, grazing days, and forage production in 2017 and 2018 for various farm fields located in western Kansas, eastern Colorado, and southwestern Nebraska.
| Location | Planting Date | Killing
Frost |
Start Grazing | End of Grazinga | Days Grazing | DM Yield (lbs/ac) |
| 2017b | ||||||
| Oberlin, KS | 7/10 | 10/27 | 12/8 | 1/9 | 32 | 2143 |
| Idalia, CO | 7/8 | 10/30 | 9/15 | 10/30 | 33 | 1886 |
| Vona, CO | 7/18 | 10/27 | – | 11/15 | Not grazed | 514 |
| Seibert, CO | 9/11 | 10/27 | – | 12/5 | Not grazed | 816 |
| 2018c | ||||||
| Oberlin, KS | 7/20 | 10/15 | Too wet to graze | 2294 | ||
| Seibert, CO | 7/9 | 10/14 | 12/17 | 2/12 | 57 | 1236 |
| Bird City, KS | 7/7 | 10/14 | 1/14 | 2/15 | 32 | 856d |
| aIf field was planted, but not grazed, date represents when forage production data were collected. | ||||||
| bOn per acre basis, mix composed of 20 lbs triticale, 6 lbs Austrian winterpea, 4 lbs sorghum-sudangrass, 4 lbs cowpea, 3 lbs sunflower, 2 lbs millet, 1 lb radish, 0.5 lbs rapeseed, and 0.2 lbs phacelia. | ||||||
| cOn per acre basis, mix composed of 20 lbs triticale, 4 lbs Austrian winterpea, 4 lbs sorghum-sudangrass, 5 lbs cowpea, 1 lb sunflower, 2 lbs millet, 1 lb radish, 0.75 lbs sunn hemp, 0.5 lbs rapeseed, and 0.2 lbs phacelia. | ||||||
| dForage sample collected 4/2 | ||||||
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. Grazing a stocker only herd or the inclusion of stockers with cows and calves makes it easier to add or subtract animals based on differences in carrying capacity among years. 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 dry years, grazing annual forages can help native range from being overgrazed or the need for supplemental feed. If excess forage is produced, putting some up as either hay or silage is a good option to preserve forage for dry years. However, this could potentially reduce residue amounts and negate soil health goals as less residue is typically left in the field with hay/silage removal than with carefully managed grazing. However, a long-term study at SWREC found no differences in soil physical or chemical properties between a cover crop left standing or hayed with 6” residue, and both improved soil physical properties compared to fallow.
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 precipitation allows ample forage production, grazing pressure could be reduced on native pasture or delayed until the dormant season, both steps that could benefit long-term range condition.
Contributors – Sandy Johnson, Extension Beef Specialist (Colby), Augustine Obour, Soil Scientist (Hays), John Holman, Cropping Systems (Garden City), K-State Research and Extension; Joe Brummer, Extension Forage Specialist, Angie Moore, Research Associate, and Meagan Schipanski, Assistant Professor, Colorado State University, Soil and Crop Sciences. For more on this project see DrylandAg.org.
