Factors to consider:

Potential effects on yield of late planting corn

Several studies have been done to examine the relationship between planting date, final plant population (not planting rate), and yield.

In this week's CropWatch, also see Options for using corn killed at various stages

Table 1 (below) illustrates the summary of yield responses to population for corn planted at varying dates in research conducted by the University of Illinois. Regardless of planting date, optimum grain yield occurs for most situations within a similar range of final populations.

From the table you can see that the optimum final plant populations are very similar for early and late planted corn but there are situations where one would consider a change in planting rate with delayed planting.

Situation 1
With the normal maturity hybrid since the establishment rate may be 95% for late planting vs 85 to 90% for earlier planting date one may reduce the planting rate accordingly. It also is possible that conditions may be too wet when planting and crusting etc. may occur. If one feels that establishment rate will actually decrease from earlier planted corn - one may increase the planting rate.

Situation 2
If you change to an earlier maturity hybrid, consider increasing the planting rate by several thousand. Increasing the seeding rate by up to 20% may be warranted. Consult your seed company for additional information.

Situation 3
Later planted corn is taller than earlier planted corn which also results in higher ear placement. Higher planting rates (smaller stalks) and taller corn increase the possibility of lodging. If lodging is a concern, consider reducing planting rates to the low end of the suggested planting rate.

Delayed planting does shorten the growing season. Research by Bob Nielsen (Purdue University) and Peter Thomison (Ohio State University) shows that corn hybrids adjust well to delayed planting and adapted hybrids can be planted into early June without major risks of fall frost injury. Nielsen and Thomison found that delayed planting decreases hybrid GDD to physiological maturity (black layer) by about 6.8 GDD per day. Thus, full season hybrids can be planted much later than we used to think they could be and they will still mature before the risk of fall frost is high. With the 6.8 GDD loss per day with delayed planting, a hybrid planted on May 30 would behave much like a hybrid with 204 less GDD planted on May 1.

Table 2 combines the relationship of CRM and GDD with the concept of reduced GDD requirements for delayed planting. A 115 CRM hybrid (2782 GDD) planted on May 15 would behave like a 111-CRM hybrid and when planted on May 30, it would behave like a 107-CRM (2578 GDD) hybrid. If planted on May 30, this hybrid would mature around September 14 in southeast and southern Nebraska and around September 27 in central and northeast Nebraska.

For most of the Nebraska corn production area it is not necessary to change hybrids until early June if the hybrid requires 115 CRM or less. A consideration is kernel moisture at harvest with high drying costs. With the same planting date a hybrid with a 5 unit higher RM will have 2.5% higher moisture content at any date in the fall.

There are greater differences in kernel moisture between different CRM corn hybrids planted late. For example, 108 and 97 CRM corn hybrids planted on April 21 had a 5% difference and when planted June 1 had a 16% difference in kernel moisture in the fall. If planting dates are delayed into mid-June, consider crops other than corn.

Bob Klein
Extension Cropping Systems Specialist
West Central REC, North Platte

Table 1. Expected corn grain yield due to various planting dates and final plant populations. Planting date Plant population (final) per acre   10,000 12,000 14,000 16,000 18,000 20,000 22,000 24,000 26,000 28,000 30,000 32,000  34,000 36,000   Percent of optimum yield 4/10 62 68 73 78 82 85 88 91 92 93 94 94 93 91 4/15 65 71 76 81 85 88 91 94 95 96 97 96 96 94 4/20 67 73 78 83 87 90 93 96 97 98 99 98 98 96 4/25 68 74 79 84 88 92 94 97 98 99 100 100 99 97 4/30 68 74 79 84 88 92 95 97 99 100 100 100 99 97 5/5 67 73 79 83 87 91 94 96 96 99 99 99 98 97 5/10 65 71 77 82 86 89 92 94 96 97 97 97 96 95 5/15 63 69 74 79 83 87 89 92 93 94 95 95 94 92 5/20 59 65 71 75 80 83 86 88 90 91 91 91 90 89 5/25 55 61 66 71 75 79 81 84 85 86 87 87 86 84 5/30 49 55 61 65 70 73 76 78 80 81 81 81 80 79 Souce: Nafziger. 1994. J. Prod. Ag 7:59-62.

Copyright 2006 by the University of Nebraska Board of Regents. All rights reserved.

Published by University of Nebraska-Lincoln Extension in the Institute of Agriculture and Natural Resources Cooperating with the counties and the U.S. Department of Agriculture.

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