With soils continuing to be very wet in parts of Kansas and with the 8-14 day outlook projecting wetter-than-average conditions (particularly for eastern Kansas), more questions have been coming in about the effect of delayed planting on corn yield. A series of studies at K-State looking at delayed corn planting was conducted a few years ago.
Three hybrid maturities were tested: 100-, 108-, and 112-day. Over the two years and three locations (Belleville, Manhattan, and Hutchinson) of these studies, there were three distinct environments (as related to the environmental stress):
- Low Stress – where rainfall was favorable during the entire growing season
- Early Stress – where cool temperatures and wet conditions limited early corn growth
- High Stress -- where conditions (rainfall and temperatures) were favorable early in the season, but the mid-summer was hot and dry
In the Low Stress environments, yields were reduced by less than 20% when planting was as late as mid-June. Yields were not statistically different for any planting date before May 20 (starting from early April). Maximum yield in these non-irrigated environments was 176 bu/acre. The yield responses were similar for hybrids of all maturities.
In the Early Stress environments, yields actually increased as planting was delayed until late June. This response was similar for all hybrid maturities. These environments had favorable temperatures and rainfall throughout July and early August. Maximum yield in these environments was 145 bu/acre.
In the High Stress environments (hot, dry mid-summer conditions), yields dropped by about 1% per day of planting delay, depending on hybrid maturity. The shorter-season hybrids had the best yields if they were planted before late May (maximum yield = 150 bu/acre), but all hybrids had yield reductions of more than 50% when planting was delayed until early to mid-June.
Figure 1. The top chart (LS, or Low Stress) shows how little corn yields changed as planting dates got later when growing conditions were good through the remainder of the season. The middle chart (ES, or Early Stress) shows that corn yields actually increased with later planting dates when conditions were too cool and wet early, but then became more favorable. The lower chart (HS, or High Stress) shows how dramatically corn yields decreased when conditions were favorable early in the season, but the mid-summer was hot and dry. H1 refers to the 100-day hybrid. H2 refers to the 108-day hybrid. H3 refers to the 112-day hybrid.
In many ways, the current growing season is shaping up like the “Early Stress” scenario above, with cool conditions early in the season. Will this cool spring be followed by favorable temperatures and rainfall, or by hot and dry conditions during the rest of the growing season?
While long-term weather predictions are highly unreliable, the National Weather Service Climate Prediction Center (http://www.cpc.ncep.noaa.gov/) one-month (June) and three-month outlook indicates increased chances of wetter-than-normal conditions statewide (Fig. 2).
Figure 2. One-month (left-panel) and three-month (right-panel) outlook precipitation probability (from May 19, 2016). Source: NOAA.
Using a Web-Support Decision Tool: “Useful to Usable” (mygeohub.org)
To get an estimate of what may happen in various scenarios, producers may want to try the “Useful to Usable” web-support decision tool at mygeohub.org. As an example, for the Manhattan location, if a 111-comparative relative maturity (CRM) corn hybrid was planted on April 15, it will take 2,666 growing degree days (GDD) from planting to physiological maturity (black layer). That means it will reach black layer around the last week of August or first week of September (latest black layer time, Sept. 10, in the example below). The earliest first freeze experienced at this location was early October (in 1985); thus, mid-April planting does not risk early termination of the crop by fall frost (Fig. 3). Of course, we are well past that date now.
Figure 3. Corn growing degree day tool for a 111-CRM planted April 15, 2015. From https://mygeohub.org/groups/u2u/gdd (“Usable to Useful” website).
If the planting date is this Friday, May 20, without changing the CRM, the final GDD required is similar -- 2,666. Nonetheless, black layer will be reached sometime from mid-September to first week of October. This situation increases the risk of damage from an early fall freeze, but the impact is predicted to be minimal (Fig. 4). If planting is delayed even until the last day of May (May 31, 2016) without changing the CRM (111 days), then in this case the black layer would be reached sometime during the last week of September to mid-to-late October, which proportionally increases the risk of exposing the crop to the first fall frost (earliest occurring in the first week of October for this location).
Figure 4. Corn growing degree day tool for a 111-CRM planted May 20 (right panel) and May 31 (left panel). From https://mygeohub.org/groups/u2u/gdd (“Usable to Useful” website).
If planting is delayed to June 6, the same CRM corn hybrid will reach maturity sometime from about early October to the beginning of November (Fig. 5 – left panel). This will increase the likelihood of a killing frost (high probability for late-October), which will result in a low-test weight and high moisture content in the grain due to a shortening of the grain filling and drying down period. By keeping the same planting time, but switching to a shorter CRM corn hybrid (e.g. 103 CRM) (Fig. 5 – right panel), the corn would reach black layer just a week after the 111-CRM hybrid planted May 20 (Fig. 4 – left panel). If 103 CRM corn hybrid seed was not easy to find for the farmer, even switching to 105 CRM planted on June 6 will be similar to the outcome obtained for planting the 111 CRM on May 31 (Fig. 4 – right panel). Thus, changing to a shorter CRM will increase the probability of reaching maturity with a small risk of being impacted by an early fall freeze.
Figure 5. Corn growing degree day tool for a 111-CRM planted June 6 (left panel) and for a 103-CRM (right panel) planted at the same time. From https://mygeohub.org/groups/u2u/gdd (“Usable to Useful” website).
As you move south and east from Manhattan, the risk of early termination from a fall freeze will decrease, but the risk will increase as you move north and west from Manhattan.
So, depending on your location and what you believe will happen during the rest of the growing season, delayed planting may or may not have much of an effect on corn yields. A previous eUpdate (April 26, 2013, No. 400) article on historical yield and planting date relationships confirmed that planting date is not necessarily a strong predictor of corn yield.
When making decisions on delayed planting of corn, crop insurance considerations are often an important factor, as well as agronomic considerations.
Ignacio Ciampitti, Crop Production and Cropping Systems Specialist
ciampitti@ksu.edu
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