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April 10, 2013

Why do Corn Yields Decline with Delayed Planting?

A lot of bad things can happen to the corn crop if the planting is delayed past the normal planting period. Generally, late-planted corn yields less for a number of reasons including:

  • Late-planted corn pollinates later in the summer when weather conditions may be hotter and dryer. The success of pollination can be directly correlated with the temperatures and the amount of moisture available to the corn plant at the time of pollination.
  • Pollination generally occurs for about a ten-day period. If the temperatures are extremely hot (upper 90's low 100's) the pollen may become sterile and the pollen may flow for less than ten days.
  • Under that same extreme heat, the silks may dry out to such an extent that they are not receptive to the pollen grains that land on the silk. Each potential kernel has a silk attached to it that grows out the tip of the husks and each one of those kernels must be fertilized by a pollen grain that lands on the silk and grows down to fertilize the kernel.
  • If the moisture is limited at the time of pollination, then the timing of the "nick" may be off. The nick is the timing between when the silks are receptive and when the pollen is being shed. Under drought situations, the emergence of the silks may be delayed and the pollen flow may be accelerated so that by the time the silks start to emerge, most of the pollen has already been shed.
  • All of these pollination issues are generally more of a concern in the southern production regions where the summertime weather may be hotter and dryer than in the northern locations.
  • Any potential pollination problems are impacted by the interaction between temperature and moisture availability. In other words, if there is ample soil moisture, then pollination is less impacted by extreme heat. Conversely, if the soil moisture is limited, then less extreme heat can result in pollination problems. The worst combination would be extreme heat and a drought, which is exactly what happened during the 2012 U.S. growing season.
  • Late-planted corn also runs the risk of not having enough time to mature before the first killing freeze in the fall. This of course is a bigger problem in the more northern locations.
  • Late-planted corn can also yield less due to the fact that it receives less total sunlight during its growth cycle. Think of a corn plant as a factory - the bigger the factory, the greater the potential production. The maximum amount of sunlight will occur on June 21st, which is the Summer Solstice. From that day forward, the amount of sunlight will diminish on a daily basis. Ideally, you want the corn plant to be as big as possible as early as possible so that the maximum leaf area coincides with the maximum sunlight. If corn is planted later than normal, the maximum leaf area only occurs after the amount of sunlight has started to decline. Therefore, regardless of how good the growing season is during the later summer, late-planted corn will have less sunlight to conduct photosynthesis than earlier planted corn. As a result, late-planted corn generally yields less than corn planted at the normal time.

Having listed all the problems associated with late planted corn, it's not a guarantee that late planted corn will yield less than earlier planted corn. It all depends on the summer weather of course. Late planted corn can do just fine if the summer weather cooperates and we have a late fall. Conversely, early planted corn may not be the best yielding as exemplified by last year when the corn was planted at a record pace, but the nationwide corn yield fell to 123 bu/ac.