There's still plenty of discussion when growing corn is the topic of the day about how thick to plant. Results from Corn Illustrated plots and many other tests around the Midwest during the last couple of years point to 28 to 30,000 plants per acre as a good goal for most hybrids in most, but not all, conditions. Droughty areas without irrigation obviously may not be able to handle these populations year in and year out.
Ah, population, that's the rub! More and more agronomists and even farmers are talking populations, not seeding rates. So if you plant 30,000 seeds per acre, that may or may not be the same as having a population of 30,000 plants per acre. Dave Nanda, plant breeder and president of Bird Hybrids, Tiffin, Ohio, says it likely won't be. He usually allows 1,000 to 1,5000 extra seeds to account for losses during germination and emergence. So if he wanted 30,000 plants per acre, he would plant 31,000 to 31,500 seeds per acre. Note this isn't what he would recommend necessarily- it's just an example of how he would boost seeding rate to still wind up with the desired population.
What that factor between seeding rate and populations should be is only partially in your control. Weather can have the final say, as it did in the Corn Illustrated plot near Edinburgh, Ind., in '08. One hybrid didn't emerge well after a cool, wet spell in May, directly after planting, and wound up some 4 to 6,000 plants short of the goal in nearly every case. The other hybrid, which was smaller in seed size and apparently planted thicker than it should have been, either met, beat or came very close to the target plant population in every case. The results were reflected in final yields. This was one of the few instances last fall where the thicker hybrid in this plot outperformed the hybrid that didn't handle the early germination problems, at least in terms of yield.
What you can control are soil conditions at planting, to some degree, by deciding when to plant and how to prepare the seedbed, and planter settings that affect seed placement in the soil. Remember what's important is positive seed-to-soil contact, Nanda says.\
Here's an example that has nothing to do with corn, but that makes the point. One year ago a gardener decided to start tomato plants from seed. He used an artificial soil mix, but didn't cover the tray after seeding. Germination was sporadic. The soil kept drying out day to day.
This year, he found half of a 1,000-seed packet left from last year. He planted the seeds using the new technique he learned this year- starting with uniformly moist soil and covering the germination tray with a plastic dome until seeds germinate and emerge. Nearly every seed must have germinated, even though the seed was a year old. He filled 9 flats, some 430 or more plants, all with healthy root systems, from that one tray- that one-half packet of seed!
The difference was in how he handled the seed after germination, not in the seed. Translate that into your planting operation and the point is to do whatever it takes to give seed the best chance to germinate in the field. Then base your adjustments between seeding rate and your plant population goal on the percentage you think is possible to achieve. Admittedly, the hardest factor to anticipate may be the weather. Make your best guess, and give it a try.