Agronomy Guide
Cooperative Extension Service, Purdue University, West Lafayette, Indiana
(Corn) AY-259
Corn Hybrid Selection for Delayed Planting
Bob Nielsen, Agronomy Department, Purdue University
Corn planting is delayed somewhere in Indiana three out of every five years because of wet spring conditions. If you are facing a later than normal planting date and you haven't planted a large portion of your corn acreage, you need to compare the risks of planting late maturing hybrids to those of planting earlier maturing hybrids. The decision to switch hybrid maturities in a late planting situation is based on: 1) how many days are left from planting until the first killing frost in the fall, and 2) how many growing degree days are expected during that time so that hybrid maturity can be matched to the anticipated accumulation.
The objectives of this publication are: 1) to discuss the impact of delayed planting on the maturation and grain yield of corn, 2) to relate traditional corn maturity rating systems to the newer growing degree day system, and 3) to provide the producer with the necessary hybrid maturity selection information for making decisions when facing delayed planting situations. General guidelines for selecting hybrid maturities at several late planting dates are provided.
Impact of Delayed Planting on Corn Maturation and Grain Yield
information gathered in Indiana over the last 20 years suggests that delaying corn planting beyond May 10 will cause grain yield losses of about 1 bushel per acre per day. Corn yields decline about 2 bushels per acre per day with delays in planting from May 20 until June 1. These yield losses are due primarily to the shortened part of the growing season from planting to tasseling. This is the time during which the corn plant is building its photosynthetic factory.
Towards the end of May, however, delayed planting can also reduce yield if the grain does not reach physiological maturity before the first killing frost in the fall. Physiological maturity is that point in time when the kernels reach maximum dry weight and a black layer of cells forms near the tips of the mature kernels. This black layer can be used to identify the occurrence of physiological maturity. Moisture content of the grain is approximately 30-35 percent at this time.
If the corn is frosted before it is physiologically mature, the grain will be lower in test weight and may not dry down properly. Frosted corn usually leads to added harvesting problems and higher drying costs. Proper hybrid maturity selection in a late planting situation will help avoid this potential problem.
Maturity Rating Systems for Corn
Before continuing, working definitions are needed for hybrid maturity and what we mean by early, medium, and full-season hybrids; days to maturity; and growing degree days.
A full-season hybrid is defined as one that uses the complete growing season. Early- and medium-maturing hybrids, therefore, require a shorter growing season than full-season hybrids Because earlier maturing hybrids do not utilize as much of the growing season to produce grain, they will usually produce lower grain yields than fuller-season corn hybrids. This is why full-season hybrids are normally recommended for planting a major share of your corn acreage. The terms “early," “medium," and “full" are relative to each other and specific to a location and a planting date For example, a medium-season hybrid in northeast Indiana may be rated as an early hybrid in central Indiana. Similarly, an early-season hybrid planted on May 1 may “become" a full-season hybrid when planted on May 27.
The days to maturity rating system is probably best known among corn producers. This type of relative maturity system does not provide you with an absolute number of calendar days from planting to maturity. For example, a 115-day hybrid may require 100 days from planting to physiological maturity during a warm growing season and 130 days during a cool growing season. The days to maturity system instead ranks hybrids in relative order of maturity based on harvest grain moisture percentage compared with check hybrids. For example, a 125-day hybrid would have a greater harvest grain moisture than a 110-day hybrid if harvested on the same day.
We need to be able to accurately measure maturity or growing season requirements to make