Preliminary research: seeding cover crops early into standing corn
A common theme I am hearing when speaking with farmers across the state has emerged: can we try to seed cover crops into corn earlier in the season? A conversation about seeding cover crops into corn around the V7 stage of corn development even sprung up earlier this week on the Practical Farmers of Iowa cover crops email discussion list. The two major issues are: 1) What will establish and persist beneath the corn canopy? and 2) How might seeding a cover crop this early affect crop insurance coverage?
Last summer, John Gilbert, who farms near Iowa Falls in Hardin County, set out to test a wide array of cover crop species seeded into corn at five different dates through the growing season. As John would tell it, “The general outline was to use three cover crop mixes in standing corn, with small plots hand seeded at two week intervals to evaluate stand establishment potentials, survival and timing.”
The mixes John evaluated were:
- Cereal rye, oats, hairy vetch, and alsike clover (fall and spring cover)
- Oats, cereal rye, rapeseed, and mammoth red clover (forage to supplement cornstalk grazing)
- Annual ryegrass, oilseed radish, and crimson clover (fall cover only, commercial mix from Albert Lea Seed House)
The cover crop seeding dates were:
- Mid-July (corn fully tasseled)
- Early August
- Early September
Before the first seeding date, corn was cultivated and received a side-dress N fertilizer application. John explains, “Each of the three mixes was seeded twice (two reps) and covered six rows width by about 15 feet long (roughly square), using a checkerboard type pattern to leave unseeded areas between plots in the rows, and in adjacent rows. Seed was spread using a hand-crank, spin type seeder under the canopy. No attempt was made to keep seeding rates even, or to match amount used in field scale planting. The objective was to insure enough seed was applied to be enough for evaluation.”
According to John: “After each seeding, enough rain fell to germinate the seed before the next seeding date. Corn harvest was made about Oct. 23. A hard killling freeze came on Veterans Day, ending the growing season for all plots. Evaluations of stands and species were made after the freeze. General observation was the grasses (small grains) were predominant except in the earliest corn seeding, which by harvest was mainly rape. In general it’s hard to determine whether any of the perennials established well, but it appears early seeding may be too shaded for good survival.”
In November, after the hard freeze, John snapped photos of one rep of each mix at each seeding date. Row 1: Mix #1 (yellow flags); Row 2: Mix #2 (blue flags); Row 3: Mix #3 (orange flags). Column 1: Mid-July seeding date; Column 2: Early August seeding date; Column 3: Mid-August seeding date; Column 4: Early September seeding date; Column 5: Mid-September seeding date.
John rated each of the three mixes:
- Mix #1: Good small grain germination, fair hairy vetch germination and marginal alsike establishment. More evidence of the vetch and clover was present before harvest than at freeze-up. Spring will be the test to see if any broadleaf species survive. At freeze-up there was little difference visually between seeding dates, although growth seemed slightly more dense under corn stalks.
- Mix #2: Although the small grains germinated with the earliest seeding, they had poorer survival at harvest than later dates. Rape did persist in the absence of the small grains. Little clover appeared in seedings from early and mid-September. The forage value would have been disappointing for fall grazing, but spring potential is an unknown.
- Mix #3: Establishment of the ryegrass was good, but little evidence of the other species under the crop canopies. The earlier seeding dates tended to grow taller, but quite spindly ryegrass. This mix was also used to over seed a field of beans and to keep ponds where beans drowned out from growing up to weeds. In beans the results were similar to our plots with good germination but not a lot of biomass growth. In ponds where seeding was done in late July without any competition (lightly disked in), all species showed good expression, with ryegrass reaching about three feet and radishes being significant.
This summer, John is going to use the information he gleaned from these small, hand-seeded plots to choose cover crop species to seed into corn in larger strips. Stay tuned for more on this, including a PFI Cooperators’ Program research report this fall!
Disclaimer: if considering seeding cover crops early into corn, contact your crop insurance agent about how this may or may not affect your coverage! Right now this appears to be a gray area as seeding cover crops this early is a new technique in this region.