Reports are coming in from farmers who cannot find seedlings in fields that received aerial application of cover crop seeds in late summer.
"This is not an uncommon phenomenon. Broadcasting seed on the soil surface is a very risky undertaking, and the more so in long-term no-till," says Sjoerd Duiker, Penn State soil management specialist. "While the idea sounds good, and there are reports about successful establishment of cover crops with aerial seeding, the lack of seed-to-soil contact and soil coverage may lead to stand loss or failure."
Duiker says activity of ground-dwelling organisms is high in no-tillage, and there could be a host of seed predators, as well as slugs. Additionally, if there is heavy dew or some limited rainfall, he says the seeds could germinate and subsequently dessicate when they don’t find moisture in the soil.
There are also reports about increased heaving of winter grains broadcast on the soil surface due to limited anchoring in the soil.
Duiker offers the following tips for increased success with broadcast application of cover crop seed:
1. Frost seeding red clover or perhaps yellow sweet clover in February to March in small grain. Soil moisture is generally sufficient for germination and early growth and perhaps ground dwelling herbivores are not yet very active.
"However, even here we often see spotty clover stands," Duiker says. "Yellow sweet clover can be quite aggressive and may be as high as the small grain at harvest, which can add to the challenges."
2. Some limited tillage, such as with Turbo-Till or Aerway implements, or light discing may give the seed-to-soil contact needed, but this is not an option in standing crops.
"Considerable effort has gone into developing and fine-tuning planters and drills," Duiker says. "The reason is that precision placement of seeds pays. Unfortunately, there are limited options to drill through a standing corn or soybean crop."
Meanwhile, Ron Hoover, on-farm research coordinator for Penn State, has reported preliminary results of cover crop strip plots conducted this year.
Two plantings of most of them, single species and mixtures of species, were recently completed at 11 locations across Pennsylvania. Here are a few of the early observations.
Cereal Rye — While the rye plots aren’t as tall as oats, wheat or triticale, they are found to be exhibiting some allelopathy against other species growing with the rye. The tillage radish that is being grown with rye in one strip is markedly shorter than the radish being grown with spring oats, Hoover says.
Both plots have tillage radish drilled at the same 5 pounds of seed per acre. The growth of weeds in and around the rye is often noticeably less than those same weed species found outside the plots. Small flower galinsoga growing under rye at one location is one-third to one-half as large as plants growing where there is no rye.
Wheat — "We may need to rethink using this species for an early planted cover crop," he says. "This species planted as early as late August could serve as a host for Hessian Fly. While it is true that fly damage in a wheat cover crop is not much of a problem, the fly may travel in the spring to wheat fields being grown for grain production."
Tillage Radish — This entry is looking very good, Hoover says. Drilling 5 pounds per acre in combination with either rye or oats has resulted in plots where there isn’t excessive competition between the radish and small grain.
"Earlier work indicated that radish, with its rapid growth and characteristic large leaves, can easily dominate a mixture," Hoover says. "Ten pounds of radish drilled alone is showing signs of nitrogen deficiency, indicating this species’ ability to take up and hold on to nutrients soon after establishment."
Crimson Clover — This species looks very good at all locations. It was drilled at 15 pounds per acre into plots with oats (40 pounds per acre) and into other plots with annual ryegrass (10 pounds per acre).
"Early indications are that, at least for earlier seedings, we may be able to reduce the seeding rate below 15 pounds per acre," Hoover says. "It will be interesting to see how good the 15-pound rate looks when drilled in late September.
Red Clover — While Hoover says he is normally not a fan of red clover planted much after early August — plants often don’t get large enough to provide the soil cover needed to minimize winter soil and nutrient losses — this year, with ample moisture at most locations, this species is showing itself very well.
"Plants are already large enough that overwintering will not be an issue, and with a few more weeks of growth, should provide an acceptable amount of biomass to protect our soil resources," he says.
Hairy Vetch — This species also looks unusually good at most locations, Hoover reports. The 15-pound seeding rate has provided good plant density, and early plant vigor is great.
"Will an abnormally late killing frost at some of the southern locations result in so much fall aboveground biomass that overwintering ability may be compromised? We’ll know in the spring," he says.