Impact of cold, wet weather for Iowa corn production

Encyclopedia Article

By R. Elmore and L. Abendroth

11 Apr 2007 -

Rain and snow across all of Iowa on the 10th and 11th of April, along with the prior week’s cold and wet weather is causing some concern among corn producers. In addition, more rain/snow is forecasted for later this week. How does the recent weather impact corn planting progress, yield potential, and other agronomic factors? The possibility of delayed planting is a legitimate concern, considering that Iowans intend to plant 10% more corn in 2007.  

Iowa corn planting dates have become progressively earlier over the last 3 decades. Half of the 2006 crop was planted by 25 April, more than 2 weeks earlier than during 1975-1979. The time required to plant all of Iowa’s corn acreage in 2006 was approximately 6 weeks, from 16 April – 28 May. Using a linear scale, this equates to about 315,000 acres planted per day. If 2007 planting intentions are carried out, Iowa producers will need about 4 more days to plant the expected increase of 1.3 million acres of corn, if using last year’s pace of planting.  

Four days does not sound like much of an addition, given normal weather in the spring. Yet this year, it appears that the best we might expect to start planting is during the week of 23 April; a week later than last year. If producers keep the same planting pace as in 2006, we could expect planting to be finished during the first week of June.  

In a recent issue of the Integrated Crop Management (ICM) newsletter, the most recent planting date response data is discussed. Optimum yields were obtained between 15 April and 15 May. Using a conservative estimate, yields decreased approximately 0.75% per day after this optimum period.  At a yield level of 180 bushels per acre that is equivalent to 1 1/3 bushel yield reduction per day. The percent loss value is an estimate, and will vary based on location, year, etc. If planting starts during the week of April 23rd and proceeds at a pace similar to that of 2006, then 80% of Iowa’s corn should be planted by mid May, thereby realizing full yield potential. 

There are two cautions to consider. First ‘mudding’ in corn will decrease yield potential not only in the short term (through reducing plant stands and resulting in more variable plant emergence rates), but also can have long-term impacts such as poor root development ensuing from soil compaction. The long-term impacts from soil compaction can plague growers for years. Second, most seed companies have reported that the more popular hybrids are already sold; many of these are transgenic hybrids. If large areas of corn need to be replanted this year, supplies of the popular hybrids will be limited, if available at all. The best plan is to keep the seed in the bag and the planter in the shed until seedbed conditions are conducive for planting corn.

Iowa State University Agronomy Extension Corn Production