When smaller corn plants compete with larger ones, they’re at a significant disadvantage in the fight for sunlight, moisture and nutrients, says Lori Abendroth, Iowa State University agronomist. Meanwhile, as the smaller plants battle for whatever resources they can grab, they drag down yields of the older plants. The result: The whole field suffers.
If one-fourth of the crop emerges just a week late, yields can drop about 6%, Abendroth says. A two-week delay for half the plants sets up the crop for up to 17% loss. That’s why uniform emergence is so vital to optimum yields.
“It’s tempting to tell yourself that the crop will grow out of it [and] make up for the effects of uneven emergence later,” says Purdue University agronomist Bob Nielsen. “Uneven emergence and variable plant spacing are problems that will haunt you the whole season.”
Begin at harvest. The path toward uniform emergence starts when you harvest the previous crop and winds through the entire fieldwork and planting process. Agronomists point to several critical steps to help give every plant in the field a good shot at forming an even stand.
Manage residue. Soil under heavy residue will be colder than soil in bare patches. Using chopping corn heads and chaff spreaders at harvest can help, especially in no-till fields. In the spring, vertical tillage and row cleaners, or what Nielsen calls “trash management gadgets” — whippers, wipers, movers or fingers — can clear residue and clods out of the row so the soil warms up evenly.
Optimize drainage. One of the big payoffs of tile drainage is in uniform emergence, thanks to warmer soils, better tilth and more even soil moisture across the field.
Wait until the field is ready. Monitor both soil moisture and soil temperature. If you work or plant a wet field, it can create enduring soil compaction problems, which can play havoc with emergence. Cold soil can stall emergence and leave seed vulnerable to insects and pathogens. Bill Wiebold at the University of Missouri says waiting until soil temperatures are at least 50 degrees F is the best way to lower your risk of poor emergence. The closer you are to that critical germination temperature, the more impact temperature variability can have on emergence uniformity, adds Nielsen.
Pay attention to soil conditions. The moisture and tilth of your soil this spring should dictate your tillage decisions and how you manage your planter — everything from seed depth to speed to down pressure to adjusting your closing wheels.
Tune up your planter. Make sure your opening disks are sharp and set to the proper depth, and that they don’t smear the sidewall. Check to see that seed handling parts are in good shape, and that closing wheels are adjusted to firm the soil around the seed for good seed-to-soil contact while leaving soil above the seed loose enough for easy emergence.
Match depth to soil moisture. Check fields to see where the soil moisture is, and make sure you plant seeds into the moist zone. Depending on springtime conditions, you could end up planting as deep as
2.5 to 3 inches. Don’t plant any shallower than 1.5 inches, cautions Abendroth — shallow seed placement increases the risk of uneven germination and leaves the main root system too shallow.
Watch your speed. “Excess planter speed is the biggest killer of uniform seeding depth and emergence,” says Mike Zwingman, agronomy research leader for United Farmers Cooperative in York, Neb. Even if your planter’s brochure says it can meter seed at 7 to 8 mph, stick to speeds of 4 to 5 mph to reduce bouncing and help ensure uniform depth and spacing.
The bottom line, according to Roger Elmore, Iowa State University Extension corn specialist, is this: “Time spent carefully adjusting your planter and speed for conditions specific to each of your fields will pay!”