Late Corn Planting: Don’t Get Nervous Yet
By Bill Mahanna
Not a day goes by in late-April to mid-May that I am not asked how corn planting is coming along in Iowa.
The U.S. Department of Agriculture's crop reports show that this is the slowest start to corn planting in Iowa in 20 years. As of mid-May, only 15% of Iowa's corn acreage was planted, compared with 86% in the unusually mild spring of 2012. The current cold, wet spring resulted in USDA lowering yield estimates by 5.3 bu. per acre from the 163.5 bu. the agency had predicted in February.
The good news is that the planting delay due to snow and rain has left most of Iowa in good shape regarding soil moisture.
Despite the potential yield loss due to a wet spring, planting intentions suggest a harvest of more than 97.3 million acres of corn, the largest since 1936, when 102 million acres were planted.
The increased acreage means that a below-average yield will result in a record crop that is upwards of 30 bu. per acre better than last year's average across much of the drought-affected Corn Belt.
Late is Better?
Iowa State University recommends planting corn in Iowa between April 12 and May 18 to achieve 98-100% of the crop's grain yield potential (Pierson and Elmore, 2013). The advent of bigger planters, larger, well-tiled fields and global positioning system technology allows growers in Iowa to plant more than 1.4 million acres per day against about 14 million corn acres (Elmore, 2011a).
Many producers use soil temperature (greater than 50 F) as a guide for to start planting. Time to emergence in the field ranges from more than 3 weeks for soil temperatures of 50-55 F to less than 1 week for soil temperatures of greater than 70 F.
Soil temperatures are typically not a factor if planting in May, when the condition of the seedbed becomes more of a limiting factor (Iowa State University "Corn Planting Guide," 2001).
Advances in evaluating seed genetics and seed coating treatments have allowed for reduced negative effects of planting into cold, wet soils.
Iowa State University Extension corn agronomist Roger Elmore went on record as saying that 2013 may be the year when late planting is just as good as early planting. This is because corn planted in early May will have delayed emergence that potentially causes reduced viability and stand counts, as opposed to later-planted corn that will germinate and emerge in as few as 7 days.
Elmore also reported that newer genetics and a streak of warm, dry weather can turn things around in a hurry (Curtis, 2013).
Much of the later-planted corn also did better last year.
According to Iowa State University, on April 26, 2012, Iowa soil temperatures ranged from 58 F to 64 F but dropped to a range of 49-53 F by April 29. This swing in 2012 temperatures, coupled with rain, resulted in many reports of lower yields for corn planted April 22-26 than fields planted much later (Pierson and Elmore, 2013).
It takes a coordinated effort for proper emergence to occur so that the coleoptile - the pointed protective sheath covering the emerging shoot - is pushed above the soil surface, allowing the first leaf to unfurl. This sequence of events can be compromised due to fluctuations in soil temperatures that cause the seed to absorb (imbibe) water at less than 50-55 F.
This is termed "imbibitional chilling damage," where brittle cell membranes can rupture and cause abnormalities such as corkscrew or fused coleoptiles, which is further aggravated by leaked cell contents inviting pathogen invasion (Mahanna and Thomas, 2013).
The potential for cold-water damage decreases as seedlings emerge and if initial imbibition occurred above 50 F. This partially explains why early-planted corn followed by warm weather tends to emerge better than later-planted corn emerging into cold weather or snow cover.
Emergence damage caused by cold, wet soils is generally irreversible and difficult to detect because it take several weeks for the problems with stand density/ uniformity to become visible (Mahanna and Thomas, 2013).
Critical Growth Stages
Delaying planting until soil temperatures and seedbed conditions are optimum encourages higher, faster and more uniform emergence, followed by more rapid growth and development.
However, the planting date is only one of many yield factors. Seed genetics, field management and growing conditions for the remainder of the season can be even more important to yield.
Sometimes, it is just dumb luck that results in higher yields, as was the case in some of the later 2012 plantings that missed high temperatures during pollination. High temperatures will not severely stress corn pollination if soil moisture is adequate, but last year was unusually dry.
In corn reproduction, the silks grow about 1.0-1.5 in. per day and continue to elongate until fertilized. Drought stress slows silk elongation but accelerates pollen shed. This can result in pollen shedding before the silks emerge.
Temperatures greater than 95 F with low relative humidity will desiccate exposed silks. Pollen is no longer viable once temperatures reach the mid-90s or greater, especially with low relative humidity. Pollen shed usually occurs from early to midmorning, when temperatures are lower. Couple this with the fact that the pollen shed from 1 plant is sufficient to pollinate 10 other plants, which improves the odds of success in a stressful environment (Elmore, 2011b).
This is another reason why growers plant hybrids with varying maturities - or growing degree units - until silking to spread out risk during pollination (Table 1).
Starting at about the V6 stage of growth (6 visible leaf collars), a corn plant will begin to determine yield potential. It is during this period when the number of kernels around the ear, or ear girth, is determined. For this reason, minimal stress at this time is essential for plants to maximize ear girth potential (Mahanna et al., 2013).
V6 to tasseling (VT) represents the rapid growth period when the plant will be utilizing nutrients from the soil at the maximum rate. Soon after VT, the "overall" ear size is determined. This includes girth that was determined at V6 and the number of kernels per row, or overall ear length. Ear length is set during a period of rapid growth for the plant. Water and fertility requirements are significant during these stages, and shortages can reduce yield (Mahanna et al., 2013).
Once the pollination stage begins, the maximum yield potential has already been set within the plant, and only environmental factors such as drought, late-season insects, disease and environmental events (e.g., hail, high wind) will negatively influence the final harvestable yield.
Corn raised for silage will usually be harvested during the R5, or full dent, stage but prior to black layer formation, or physiological maturity, of the kernels (Mahanna et al., 2013).
Despite the fact that later planting dates may not have a huge yield impact, northern Corn Belt growers also could face the economic impact of increased drying costs. Assuming that it requires about 0.02 gal. of liquid propane gas to lower the moisture level of 1 bu. of corn by 1 percentage unit, drying costs can approach approximately $1.00/bu. (Lauer, 2013a).
Couple this with seed and fertilizer costs that have more than tripled and cash rent that has more than doubled since 2000, and the total cost of corn production, based on information from Iowa State University, rose from $351 per acre in 2000 to $777 in 2013 (Hofstrand, 2013).
Research conducted over 10 years in southern Wisconsin (Lauer, 2013) shows that the planting date that maximized forage yield occurred on April 24, nearly 4 days earlier than the planting date that maximized grain yield in the same plots. However, the planting date window is wider for silage than for grain, with forage yields still within 95% of maximum yield on May 15 (Lauer, 2013b).
The size of the plant is not affected by the planting date. The number of leaves and the size of the stalk, shank and husk are largely genetically controlled. The digestibility of the stover was close to a flat line across the range of planting dates; however, starch content did decrease with a later planting date.
When yield and quality were combined using the University of Wisconsin Milk2006 performance index, milk per ton (quality) was not affected as much as milk per acre (quantity) due to the forage yield loss resulting from reduced starch deposition (Lauer, 2013b).
The Bottom Line
Many factors besides planting date influence corn grain or silage yields. If corn is in the ground by about May 20 in most of the Corn Belt, grain yields should be close to 90% of their potential - assuming that weather for the remainder of the growing season is forgiving.
The planting date window is even wider for silage than for grain in order to achieve yields close to the plant's genetic potential (Table 2). Increased planting intentions coupled with rejuvenated midwestern soil moistures are positive factors heading into the 2013 growing season.
Curtis, P. 2013. ISU expert says slow start to corn planting may be a good thing.
Elmore, R. 2011a. How much corn can we plant on a good day in Iowa.
Elmore, R. 2011b. How high temperatures and stress affect corn pollination.
Hofstrand, D. 2013. Cost-price squeeze emerging for corn farmers. AgMRC Renewable Energy & Climate Change Newsletter. April.
Iowa State University Corn Planting Guide, 2001. PM 1885.
Lauer, J. 2013a. The "double-whammy" of delayed corn planting.
Lauer, J. 2013b. Planting date effects on corn silage yield and quality.
Mahanna, B., B. Seglar, F. Owens, S. Dennis and R. Newell. 2013. DuPont Pioneer Silage Zone Manual.
Mahanna, B., and E. Thomas. 2013. Is early planted corn worth the effort? Hoard's Dairyman. April 10. p. 256.
Pierson, W., and R. Elmore. 2013. Planting corn late does not foretell low yield. Iowa State University Extension.