With soils continuing to be very wet in parts of 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 (Figure 1).
Three hybrid maturities were tested: 100-, 108-, and 112-day. Over the two years and three locations (Belleville, Manhattan, and Hutchinson), there were three distinct growing season environments (as related to the environmental stress):
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 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 (max. yield = 150 bu/acre), but all hybrids had yield reductions of more than 50% when planting was delayed until early to mid-June.
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 less reliable, the National Weather Service Climate Prediction Center (http://www.cpc.ncep.noaa.gov/) three-month outlook indicates a 40% likelihood of above-normal precipitation and below-normal temperatures for most of the state.
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.
Using Web-Support Decision Tool: “Useful to Usable”
A web-support decision tool called “Useful to Usable” (https://hprcc.unl.edu/gdd.php) can help in making hybrid maturity decisions when planting late. For example, for the Manhattan location, if a 111-comparative relative maturity (CRM) corn hybrid will be planted in May 31, 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 September. The earliest first freeze experienced at this location was early October; thus, planting in late-May presents a small risk for early termination of the crop by the first frost (Figure 2).
Figure 2. Corn growing degree day tool for a 111-CRM projected to be planted in May 31, 2019. From https://hprcc.unl.edu/gdd.php (“Useful to Usable” website).
If the planting date is delayed until June 15, without changing the CRM, the final GDD is the same, which may not hold true due to less GDD requirement since the hybrid is planted at later calendar date. Black layer will be reached sometime from mid-to-late October. This late planting situation clearly increases the risk of damage from an early fall freeze (Figure 3), 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 (June 15), but switching to a shorter CRM corn hybrid (e.g. 105 CRM), corn would reach black layer about the same time as the 111-CRM hybrid planted May 31 (Figure 4). Thus, changing to a shorter CRM would increase the probability of reaching maturity with a small risk of being impacted by an early fall freeze.
Figure 3. Corn growing degree day tool for a 111-CRM projected to be planted in June 15, 2019. From https://hprcc.unl.edu/gdd.php (“Usable to Useful” website).
Figure 4. Corn growing degree day tool for a 105-CRM projected to be planted in June 15, 2019. From https://hprcc.unl.edu/gdd.php (“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.
For a new GDD tool with more focus on Kansas information, the Kansas Mesonet has a Degree Days page – http://mesonet.k-state.edu/agriculture/degreedays/ – is designed to provide greater flexibility to our users, including options to select the time period and more built-in calculations.
Below are examples of using this tool, looking at May 31 for planting date at a Scandia location. For this scenario, looking to the 2018 growing season, corn will reach maturity close from mid-to late October.
Figure 5. Corn growing degree day tool for a corn hybrid planted in May 31 in Scandia, KS, reaching maturity by early to mid- October (Kansas Mesonet).
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.
When making decisions on delayed planting of corn, crop insurance considerations are often an important factor in addition to agronomic considerations. For more information on hybrid selection and crop insurance considerations, see the companion article in this eUpdate issue, “Late planting of corn: Hybrid selection and crop insurance considerations”.
Kraig Roozeboom, Cropping Systems Agronomist
Ignacio Ciampitti, Crop Production and Cropping Systems Specialist