Timing for Aerial and “Over-the-Top” Cover Crop Applications

This time of year we begin advising on proper seeding times when using aerial equipment. When aerial seeding, consider the ideal planting window for the cover crop being planted. For example, brassicas and most non-overwintering legumes typically need 4-6 (and preferably 8-10) weeks of growth prior to winter termination to reach their full potential.

Map shows average first 28⁰ date across the country. Continued temps in the 20’s will stop many cover crops from continued growth. See pg. 17 of our Management Guide for USDA Hardiness Zones of different cover crop options.

This planting period must be taken into account to coincide with the proper maturity stage of the crop in the field. Moisture or irrigation is critical when surface seeding to make up for lack of seed-to-soil contact. When time could be a hurdle, aerial and “over-the-top” seedings offer a worthy alternative. Assuming seeding intervals match, the ideal time to aerial seed into cash crops are:

  • Corn: Formation of black layer, or when at least 50% of sunlight reaches soil surface. This can be adjusted earlier if needed, as we’ve seen more timing flexibility into corn than soybeans. Sunlight is imperative, but moisture is even more important as the calendar turns to late Aug. and Sept.
  • Soybeans: Between leaf senescence and 5% leaf drop, but that depends to some degree on row width and soybean architecture. Delaying applications into soybeans decreases seed-to-soil contact and increases risk of poor moisture retention needed for maximizing germination. Getting cover crop seed below the leaves that drop is crucial for success!
  • Sunflowers: Back of the seed head turns yellow

When crop stage and seeding calendar do not align, always err on the side of earlier applications, especially when a moisture event is forecasted or irrigation can be planned. It’s better to have the cover crop seed in the field to begin the germination process vs. planting later, where seed may have to compete with excess cash crop residue from harvest.

Other Considerations:

  • For other cash crops, concentrate on sunlight infiltration to the soil surface. Sunlight and moisture are the limiting factors for bare surface applications.
  • Seed size and density is important as well. Larger seeded cover crops like peas present more challenges getting proper seed-to-soil contact.

Residue and overall irregularity of the soil surface also has an effect. We’ve noticed that some level of residue on the soil and “roughness” of the soil surface significantly increases the ability of cover crop seed to “catch”. The quicker we get adequate seed placement, the greater our chances of success.

Hypoxia Zone the Biggest Ever?  In case you missed it, National Oceanic and Atmospheric Administration (NOAA) scientists determined this years’ Dead Zone in the Gulf of Mexico is the largest ever, reported last week. Depending on media source, the context of these articles are drastically different. Google “hypoxia gulf of mexico” or see the stories below:

While it’s unclear what potential short term impact this news may have, it reinforces the need for our agricultural industry to accelerate the adoption of nutrient management practices. Cover crops are a key tool in the toolbox for doing so.