By Jon Paul Driver, Host of the Hay Kings Podcast
When hot, dry summers reduce cool-season hay yields, warm-season grasses like millet, sorghum, and sorghum-Sudan hybrids can fill the gap. In the latest Hay Kings podcast episode, Jeffrey “Alfalfa” Jackson of Croplan breaks down these heat-loving C4 grasses, providing a practical, field-tested guide for farmers exploring alternative summer forage crops.
Here’s an in-depth look at key takeaways from our conversation—with actionable insights to improve your warm-season forage production.
1. Understand the C4 Advantage
C4 grasses, unlike cool-season crops, thrive on heat and sun. Millet, sorghum, and sorghum-Sudan hybrids are incredibly water-efficient and productive under the right conditions. However, their success hinges on matching the crop to your regional environment—especially overnight temperatures and rainfall patterns.
Actionable Insight:
Use these crops in rotations where cool-season grasses decline or fail—particularly in July–August when daytime and nighttime temps remain high. Avoid planting in areas with consistently cool nights, as this limits growth even with adequate soil temperature at planting.
2. Seedbed Prep and Planting Precision Matter
Good seed-to-soil contact is critical, especially with small-seeded crops like millet. Loose or cloddy seedbeds delay emergence, reduce stands, and lower yields.
Key Guidelines:
-
Pearl millet: Plant at ¾” depth when soil temps reach 65°F (wait for 70°F for best vigor).
-
Sorghum-Sudan: Plant at 1–1.5” depth; also requires 60–65°F soil temperature.
-
Use a no-till drill or air seeder for even depth—fertilizer spreaders and harrows result in weak stands.
Actionable Insight:
Delay planting until soils are truly warm. Rushing into the field at 55°F or under produces weak seedlings and long-term stand issues. For precision, check soil temps early in the morning—not midday.
3. Match Fertility to Growth Duration
A major myth: less fertilizer avoids nitrate risk. In fact, unbalanced fertility increases nitrate accumulation.
Rule of Thumb:
Apply 1 lb of nitrogen per day of expected growth. For a 40-day crop, apply 40 lbs N with a 5:1 N:S (sulfur) ratio. Add 20–30 lbs phosphorus and 40–50 lbs potassium, especially if following a legume or planning for alfalfa reseeding.
Actionable Insight:
Side-dress between cuttings to maintain consistent growth and prevent nitrate spikes. Use AMS to supply sulfur when applying urea or other N sources.
4. Select the Right Variety for Your End Use
Variety traits directly affect digestibility, regrowth, and feed value. Two key traits are:
-
BMR (Brown Mid Rib): Reduces lignin, increasing fiber digestibility.
-
Brachytic Dwarf (BRI): Shortens internodes, producing leafier plants with better standability and regrowth.
Variety Selection Tips:
-
For dry hay, choose dwarf, BMR, or BRI-BMR types for higher palatability and manageable stems.
-
For silage, select tall forage sorghum or sorghum-Sudan hybrids designed for single-cut high-tonnage yields.
-
For grazing, consider sorghum-Sudan with strong tillering and regrowth characteristics.
Actionable Insight:
Higher seed cost is often offset by lower seeding rates and better feed value. Instead of planting 100 lbs of cheap seed, plant 25–30 lbs of a BMR-BRI hybrid and increase digestibility and intake.
5. Watch Your Cutting Height
Warm-season grasses have growing points that move upward as the plant matures. Cutting too low removes the regrowth potential.
Height Recommendations:
-
Millet: Cut at 6" minimum to avoid damaging regrowth points.
-
Sorghum-Sudan (non-dwarf): Cut at 6–8".
-
BRI-Dwarf Sorghum-Sudan: Can be cut at 3–4" while leaving two nodes above the soil for regrowth.
Actionable Insight:
Train crews and set equipment for higher cutting heights. Leaving a few inches now prevents disappointment later.
6. Harvest Timing and Method
Stem diameter and moisture content influence how—and when—you harvest.
-
For dry hay, use a crimper and avoid cutting beyond 40–45 days growth.
-
For baleage, wilting for 24–48 hours post-swathing improves fermentation.
-
For silage, harvest at flag leaf to early head for optimal tonnage and quality. Swathing to manage moisture may be necessary in high rainfall areas.
Actionable Insight:
If you're in humid or northern climates, favor millet for hay or invest in bale wrappers. Sorghum-Sudan often resists drying due to stem thickness.
7. Seeding Rates: Don’t Trust the Internet
Seeding rates vary wildly online. Choose rates based on variety and goal:
-
Millet: 12–15 lbs/acre (lower in dry areas).
-
Sorghum-Sudan: 25–30 lbs for modern hybrids; older varieties may need 50–100 lbs for thin stems.
-
Forage sorghum: Typically drilled at 8–10 lbs/acre for silage.
Actionable Insight:
Don’t overplant in dry zones—it increases plant competition and reduces drought resilience. Ask your seed rep for local trials before choosing a rate.
8. Plan for Rotation or Rescue Crops
Warm-season grasses are ideal after a failed spring crop or as a final cutting in aging alfalfa stands.
Practical Example:
Plant millet in June after your first alfalfa cut. It uses summer heat efficiently and gives fields a rest from declining alfalfa stands. Bonus: you can leverage the nitrogen credits from the previous legume.
Actionable Insight:
Pair millet or sorghum-Sudan with your crop rotation—not against it. These grasses won’t replace your core forage program, but they can fill critical seasonal or weather-driven gaps.
Final Thought: C4 Crops Deserve a Place on Your Farm
As climate variability and water restrictions increase, warm-season grasses offer flexible, reliable forage. Whether you’re chasing hay, baleage, or silage—or looking to graze efficiently—understanding the biology, planting strategy, and harvest timing of millet, sorghum, and Sudan grass can yield big rewards.
And as Jeffrey “Alfalfa” Jackson says: “If you like to haul manure, go ahead. If you want more efficient feed, think fiber digestibility.”
🎧 Listen to the full episode: The Warm Season Grass Guide (S7:E5)
📌 Sponsored by Krone – Dedicated to Hay and Forage Producers.