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Uneven or variable corn stand establishment can cause a significant reduction in corn yield potential, primarily because the effects begin early in the season. Variable stands may be the result of skips between plants or delayed emergence.1 Poor within row plant spacing or delayed emergence are hard to remedy because corn has a limited ability to compensate adequately for missing, late developing or crowded plants. Therefore, checking seeding depth, seed drop, and seed spacing in each field as planting begins to make sure seed placement is right for the soil conditions is one of the most important tasks a grower can do to protect corn yield potential.
Figure 1. Plant-to-plant variability from unfavorable conditions during emergence.
Non-uniform plant spacing can result in 5 to 7.5 bu/acre yield loss according to research done in commercial corn fields in Indiana.1 To determine plant spacing in a field, visit several locations and measure plant spacing in 50 feet of each planter unit. For example, a 6-inch average plant spacing is equal to 34,800 plants/acre in 30 inch rows. Make note of the number of skips or gaps between plants due to multiple seeds dropping at once. Planter adjustments or maintenance may be required to restore uniform seed placement.
Determining the correct seeding depth can be one of the biggest decisions a corn grower makes in each field during planting.1 The correct seeding depth for any given field should be based on the current soil moisture conditions and the 5 to 10-day weather forecast.
Delayed seedling emergence in corn can be caused by soil moisture variability within the seed depth zone, poor seed to soil contact, soil temperature variability within the seed zone, soil crusting prior to emergence, or herbicide, insect or disease injury to seeds. Emergence delays of about 10 days scattered throughout the field were shown to reduce corn yield by 6 to 9%, whereas emergence delays of about 21 days reduced yield 10 to 22 %, depending the number and distribution of late emerging plants were in a field.1
The bottom line is that uneven stand establishment in corn can reduce a field's yield potential from the first day you place seed in the ground. Yield losses can easily be as much as 7 to 15 bushels per acre due to combinations of uneven within-row plant spacing or uneven seedling emergence.
To determine the plant population in a field, count the number of plants in a length of row equal to 1/1000th of an acre based on row width (17 feet, 5 inch for 30-inch row spacing). Multiply the number of plants by 1,000 to get plants per acre. Repeat the process in several locations in the field for an accurate estimate.
1 Nielsen, R.L. 1997. Stand establishment variability in corn. AGRY-91-01. Purdue University. 160413160134