Evaluating thin alfalfa stands can lead to critical decisions about summer annual forages. If your stand is not thick enough (approximately 40 stems per square ft according to Dr. Marvin Hall, Penn State University), consider interseeding a summer annual such as sorghum sudan or sudangrass, or rotating to King Fisher corn for silage.
Success for Summer Annual Alfalfa Interseeding
- Ensure that a residual herbicide program will not impact your summer annual choice.
- Confirm minimum daily soil temperatures have reached 60 degrees F and predicted to stay warm. In most years this usually means taking two aggressive cuts before seeding or delaying the first cutting.
- Prior to seeding, control grasses and weeds with an appropriate non residual herbicide or if organic, consider a light discing. Summer annuals do not interseed well into grasses or weeds but work well seeded into alfalfa and red clover.
- No-till approximately ½ to 2/3 of suggested full seeding rate depending on alfalfa density.
- Seeding depth is critical
Sorghum sudans – Seed into moist soil at a minimum of 1” depth and a maximum of 2”. If soil is dry, risk is very high.
Sudangrass – Seed into moist soil at a minimum of 1/2” depth and a maximum of 1”. If soil is dry, risk is very high.
Teff – Broadcasting and cultipacking may be as effective as a very shallow no-till seeding. The key is timing before a nice rain. Risk is high, but the seed cost is low.
- Time alfalfa harvest as normal, but raise cutting height to a 4” minimum.
- Assuming interseeding was successful, apply up to 25-35 units of Nitrogen and some sulfur after first cutting on the newly seeded summer annual. If soil is healthy and high in organic matter, you may not need any nitrogen. Do not over apply nitrogen or manure.
- Test forage before feeding, including NDF digestibility and nitrates.