Alfalfa is the most critical and widely produced perennial forage crop in the upper Midwest, immensely contributing to the region’s livestock and dairy production. However, highly variable and severe winter conditions increase the risk of winter injury.
For example, during the 2012-2013 winter, nearly 1 million acres of alfalfa in Minnesota and Wisconsin experienced winter injury and winterkill. Replanting alfalfa shows very low success due to residual autotoxicity and prevented planting conditions that often coincide with winterkill and persist into the summer months.
Fortunately, warm-season annual forages can serve as valuable alternatives to fill this void and account for lost production.
Research on warm-season grasses
Initial trials conducted in Rosemount in 2013 (Experiment 1) evaluated six warm-season grasses (Table 1) and helped refine species selection for the 2014-2015 study in Rosemount and Waseca (Experiment 2).
Experiment 2 analyzed a range of forage species (Table 1) that were no-till planted into winter-killed alfalfa residue in late May or early June. In this experiment, researchers assessed forage yield and quality in response to intensive cutting management and variable nitrogen (N) fertilizer rates.
Harvest events occurred on 30-day intervals after planting for three cuts, concluding in early September.
Table 1 shows seeding rates from Experiments 1 and 2, in which species were no-till planted into winter-killed alfalfa.
Table 1: Warm-season forage grass species and seeding rates
| Forage | Species | Seeding rate | Experiments |
|---|---|---|---|
| Brown midrib (BMR) sorghum | Sorghum bicolor | 35 pounds per acre | 1, 2 |
| Sudangrass | Sorghum bicolor | 45 pounds per acre | 2 |
| Sorghum-sudangrass hybrid | Sorghum bicolor x S. bicolor var. sudanense | 35 pounds per acre | 2 |
| Annual ryegrass | Lolium multiflorum (cultivar Jumbo) | 30 pounds per acre | 1, 2 |
| Japanese millet | Echinochola esculenta | 35 pounds per acre | 1, 2 |
| Italian ryegrass | Lolium multiflorum | 30 pounds per acre | 2 |
| Teff | Eragrostis tef | 12 pounds per acre | -- |
| Red clover + annual ryegrass | Trifolium pretense + Lolium multiflorum (cultivar Jumbo) | 8 and 15 pounds per acre, respectively | -- |
| Siberian foxtail millet | Echinochloa frumentacea | -- | -- |
| Perennial ryegrass | Lolium perenne | -- | -- |
Yield and biomass
In Rosemount, teff achieved the greatest biomass, averaging 4.45 ± 0.15 tons per acre for total season production.
Annual ryegrass and the red clover and annual ryegrass mix were also among the highest-yielding treatments, but suffered greater weed pressure than teff (weed biomass is included in reported yields). Sorghum-sudangrass and Italian ryegrass were among the lowest-yielding treatments (Figure 2).
At the first cutting event, Brown midrib (BMR) sorghum was one of the highest-producing treatments. However, it didn’t regrow under intensive cutting as well as most other warm-season forages. Similarly, in Experiment 1, BMR yielded the greatest total biomass of all the grasses, producing more than 7 tons per acre when allowed to grow all season and cut once.
Effect of nitrogen rate
In Experiment 1, nitrogen rate had no effect on forage biomass, indicating adequate residual alfalfa N and efficient utilization. However, nitrogen rate did affect yield at all levels in Experiment 2 (Table 2).
Table 2: Yield totals by species and nitrogen rate (2014)
| Species | 0 pounds of N per acre | 50 pounds of N per acre | 100 pounds of N per acre |
|---|---|---|---|
| Teff | 4.22 tons per acre | 4.22 tons per acre | 4.90 tons per acre |
| Sudangrass | 3.63 tons per acre | 6.67 tons per acre | 4.59 tons per acre |
| Annual ryegrass | 3.59 tons per acre | 4.09 tons per acre | 4.39 tons per acre |
| Red clover-ryegrass mix | 3.68 tons per acre | 4.42 tons per acre | 4.27 tons per acre |
| Italian ryegrass | 3.25 tons per acre | 3.31 tons per acre | 4.17 tons per acre |
| Japanese millet | 3.02 tons per acre | 2.60 tons per acre | 3.97 tons per acre |
| Sorghum sudangrass | 3.25 tons per acre | 3.66 tons per acre | 3.85 tons per acre |
| BMR sorghum | 3.48 tons per acre | 3.67 tons per acre | 3.83 tons per acre |
Challenges
Waseca field trials experienced an extremely challenging growing season. A high percentage of alfalfa and weed regrowth following the initial glyphosate application required a second termination and planting event.
A more successful alfalfa kill was achieved, but weed persistence remained an issue. Severe weed pressure coupled with excessive rainfall in June and two hailstorms during the growing season resulted in particularly adverse growing conditions.
Successful species
Preliminary observations indicate that teff, sudangrass and BMR sorghum persisted the best under these conditions.
All other treatments were lost to weed pressure. Teff competed exceptionally well, quickly establishing a thick, uniform stand and inhibiting weed encroachment.
Teff’s weed-suppression potential calls for further investigation in future studies, as the percent of weed cover in teff treatments was often up to 80 to 90 percent less than other treatments.
Strategies for warm-season grasses
The best forage options may vary according to specific conditions, including production goals, time frame and seed cost and availability.
Corn silage
A previous study from 2002 to 2003 concluded that corn silage is often the best option in terms of tonnage and nutritive value, even when planted as late as July. BMR sorghum is highly competitive in biomass production, especially in one-cut systems, but generally has lower forage quality than corn.
Sudangrass and sorghum-sudangrass
Prior research also established that, in multiple-cut systems (e.g., three-cut systems) under favorable conditions, sudangrass and sorghum-sudangrass can produce competitive tonnage with higher crude protein, but lower energy than silage corn. Table 3 provides general comparisons of these studies.
Grazing and haying
Considering cutting tolerance and regrowth potential, the annual ryegrass options, sudangrass, and particularly teff could be more valuable in grazing (or haying) systems than corn silage. However, direct comparisons between all these grasses and corn haven’t yet been made.
Table 3 shows values from multiple studies in Rosemount. Treatments were planted around June 1 to 15.
| Crop | Row width | Total dry matter (DM): Harvest time | Total DM: Tons per acre | Total digestible nutrients (TDN) |
|---|---|---|---|---|
| 2002-2003 | -- | -- | -- | -- |
| Corn (81 day) | 30 inches | Single harvest at R3 | 5.9 tons per acre | 63.6% |
| Corn (95 day) | 30 inches | Single harvest at R3 | 6.7 tons per acre | 62.9% |
| Corn (103 day) | 30 inches | Single harvest at R3 | 7.0 tons per acre | 65.4% |
| BMR sorghum | 30 inches | Single harvest at R4 | 6.0 tons per acre | 55.7% |
| Sudangrass | 6 inches | 3 cuts | 5.7 tons per acre | 49.5% |
| Sorghum-sudan | 6 inches | 3 cuts | 5.8 tons per acre | 48.4% |
| 2013 | -- | -- | -- | -- |
| BMR sorghum | 6 inches | Single harvest at R4 | 7.0 tons per acre | -- |
| 2014 | -- | -- | -- | -- |
| Teff | 6 inches | 3 cuts | 4.5 tons per acre | -- |
| Annual ryegrass | 6 inches | 3 cuts | 4.0 tons per acre | -- |
| Sudangrass | 6 inches | 3 cuts | 4.0 tons per acre | -- |
Reviewed in 2023