Planters once again are crisscrossing fields, hopefully pacing themselves as in a long-distance race. Corn planting has begun in earnest – at least in central Iowa and likely across the state. As of last Sunday, 9% of Iowa's crop was planted, which is 7% behind the 5-year average (USDA-NASS, April 22, 2012). One-percent of the corn had emerged as of last Sunday.
You can expect a large increase in these numbers when they are reported by USDA in the next weekly report, which will be released Monday afternoon, April 30. That is unless the forecast rains are greater than expected. "Like sprinters, we're seemingly back to the starting blocks with normal soil temperatures and what appears to be a normal April - after a strange, abnormal, false start in March," observes Roger Elmore, Iowa State University Extension corn agronomist. He offers the following observations and information to help you evaluate corn emergence.
If you planted earlier and corn hasn't come up yet--dig around, check seed
Two fields in the Ames area reflect some of the developments of corn planted earlier in the month of April. The first, planted on April 4 for a date of planting demonstration on an Iowa State University farm is just emerging as of April 24… right on schedule (Figure 1). In an ICM article last week, Elwynn Taylor and Roger Elmore discussed how long it takes corn to emerge: 90 to 120 Growing Degree Days (GDD) for emergence. About 125 GDD have accumulated since April 4. With soil temperatures around 50 F, as they are now in most parts of the state, emergence should take about 3 weeks.
Seed in a farmer's field north of Ames planted on April 11 has germinated--the radical and seminal roots elongated and the coleoptile is stretching toward the soil surface (Figure 2). That field has accumulated around 80 GDD since the 11. "Based on forecast temperatures in central Iowa, we may accumulate nearly 120 GDD by this Sunday April 29, and with that, emergence," says Elmore. "As was mentioned in the ICM article, if more than 120 GDD accumulate since planting and emergence hasn't occurred, you need to check the seed's condition in the field."
Stand counts and stand uniformity are important factors to consider
"Once corn emergence occurs be sure to evaluate the surviving plant stand carefully, no matter if you expect good emergence and seedling survival or not," advises Elmore. "Both poor stands and plant-to-plant variability will lower the yield potential. Depending on the potential date of replant though, keeping the surviving stand – even if they have variable plant heights and development – may still be the best option." If you are seriously considering replanting a disappointing stand of corn, Elmore suggests you take a look at the decision-making guidelines in an article on his website, which you can find at Replanting Information)."Pace yourselves," he tells farmers at planting time. "This isn't a sprint. Keep your eyes open; run well. Observe the crop carefully and learn from it things to improve upon if not this year, then in 2013. The finish line is a long way off."