Delayed Corn and Soybean Planting and Replant Decisions

May 31, 2016
Author Ryan Spurgeon

Every year, when the calendar gets close to June, the question of whether to back off on relative maturity or not arises at least somewhere in the Hoegemeyer footprint.  Some areas this spring have been continually hit with significant rain events that have not allowed corn planting to progress. No matter what date you planted your corn, it still takes about 125 growing degree units (GDU’s) for corn to emerge. In addition, research has shown that full season corn hybrids can also adapt to GDU’s needed for growth and maturity when planted later.  For example, a corn hybrid will adjust to late planting by reducing the GDU’s necessary to reach black layer by about 6 units per day. An example would be a hybrid planted on May 20th that would require about 150 fewer GDU’s than the same hybrid planted on April 25th. Although the time required for a late planted hybrid to go from silk to black layer is increased, the time period from planting to flowering (tassel) is actually significantly reduced.  Although later corn planting dates are not beneficial overall in terms of yield response, later planting dates will help accelerate emergence out of the ground and the plant will benefit from more measurable GDU’s per day after emergence compared to significantly earlier dates.

There is a point when backing up in maturity does make sense, especially as one moves north. In general, the best chance to approach optimum yield vs. planting date is still achieved by sticking with the normal adapted corn maturity for that area until the last week of May. After that, reducing maturity by about 5 days is justified as we approach June 1st. As we enter the 2nd week of June, reducing maturity by another 5 days is justified. Beyond the 2nd week of June, planting corn is usually not advised. Note that these estimates vary some depending on the individual situation and geography. If we were able to predict a cooler than normal grain filling period (August and early September), then one might error on the side of caution and plant an earlier hybrid the closer we get to June. 
Questions regarding corn replant? Several factors come into play but as the calendar moves into the 1st week of June, more times than not, the best choice is to leave your remaining stand. Table 2 from Iowa State University gives estimated yield potential for corn at different final plant populations and planting dates.

Heavy, persistent rains have also delayed soybean planting for several areas of the Hoegemeyer footprint. Take a look at this article from UNL extension in regards to delayed soybean planting decisions and practices.
http://cropwatch.unl.edu/delayed-planting-in-soybeans  This article uses June 15 as a potential date to consider a 1/2 maturity group reduction (example would be reducing from a 3.5 RM to a 3.0 RM). However, we feel June 20 is a more relevant date for locations south of Interstate 80. As one moves north of Highway 20 in Nebraska and Iowa, June 1st can be used as a potential date for a ½ maturity group reduction (example would be reducing from a 2.5 RM to a 2.0 RM). Past situations would show that fuller season soybeans give the best chance for yield, especially as we move south, for several reasons:

1. Late planted full-season soybeans south of I-80 are not at the same risk of a fall freeze as those planted further north.
2. For the most part, short season soybeans do not move south well. Soybeans are triggered to go into reproductive mode based off daylight. They are more sensitive to photoperiod than corn. There is typically more heat as you move south, but also longer nights. Soybeans that are very early in maturity, that are planted late into a southern zone will potentially be very short and will not produce much for pods or canopy.
3. Fuller season soybeans still have the best potential to capitalize on late season rains come September and early October.

If you have specific questions about your farm, please don’t hesitate to contact someone on our Agronomy team.  We are here to ensure the long-term success on your farm!


Categories: Corn, Management, Planting, Ryan Spurgeon, Soybeans     Tags: 2016 Planting, corn, Hoegemeyer Agronomy Team, replant, replant guidelines, Ryan Spurgeon, soybeans    

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