Recommended planting rate for irrigated corn

Table 1. Suggested corn seeding rates/acre with 87% and 94% establishment with potential yields of 160 to 280 bu/ac.

Potential yield bu/ac	lb. Ear corn/A 70lb/bu	Number of 0.5 lb ears/ac	Early seeding date; 87% establishment	Late seeding date; 94% establishment rate
280	19,600	39,200	45,000	41,700
260	18,200	36,400	41,800	38,700
240	16,800	33,600	38,600	35,700
220	15,400	30,800	35,400	32,800
200	14,050	28,000	32,200	29,800
180	12,600	25,200	29,000	26,800
160	11,200	22,400	25,700	23,800

The National Corn Growers Association suggests a planting rate of 19,800 plus (50 times the expected yield in bushels). For example a yield goal of 240 bushels would be 19,800 + 50 x 240 = 31,800 seeds per acre. (How many more seeds than this need to be sown depends on the establishment rate.)

The following abstract is from a paper titled the On-Farm Assessment of Growers’ Current Corn Planting Rates by Thomas A. Doerge and E. Arnie Imholte from Pioneer Hybrid International. The paper was given at the 2005 American Society of Agronomy – Crop Science Society of America – Soil Science Society of America International Annual Meeting.

“North American farmers are planting an average of about 5,000 seeds/acre less than hybrid-specific suggested planting rates derived from small plot research. To evaluate whether this “Planting Rate Gap” is justified, agronomists conducted 353 on-farm planting rate trials throughout the Corn Belt of North America in 2003 and 2004 with the following objectives:

1. to better understand the risks and benefits of planting above and below the farmers’ current planting rates, and

2. to test whether small plot plant population research results are applicable to on-farm conditions.

"Using on-farm strip plots, cooperators planted a hybrid from Pioneer Hybrid International at their “Current Planting Rate” and at 4,000 seeds/acre above and below that level. The planting rate gap was defined as the difference between their current planting rate and the optimum plant population for their hybrid as determined by seed company research. On average, growers predicted a 6.5 bu/ac yield increase when planting 4,000 seed/ac above and a 8.8 bu/ac yield decrease when planting 4,000 below their current planting rate. For locations where soil moisture was adequate, the income advantage for planting at the higher rate was consistent with findings from small-plot research. Namely, the larger the planting rate gap, the greater the income advantage for increasing plant rate 4,000 seeds/acre.

Figure 1. Potential corn yields with varying seeding rates, planting dates and growing degree days with optimum irrigation in selected locations in Nebraska. (Link to larger version.)

"Under dry soil conditions, there was no advantage for increasing planting rates, even when growers were planting well below suggested levels. Under no circumstances was decreasing the growers’ current planting rate profitable. Growers consistently over-estimated the effects of plant population on stalk and root lodging. Small plot and on-farm trials gave comparable results at locations with adequate soil moisture. Some consideration of soil moisture status, particularly during the grain fill period may be needed to more accurately identify optimum planting rates for a given hybrid.”

Figure 1 shows the results of using the 2006 version of Hybrid Maize and the potential corn yield with optimal irrigation. Note that the populations are final plant density at maturity and not the number of seeds sown per acre. If the stand counts are not known, they suggest using a plant population that is 94% of the number of seeds sown.

In using this information one should estimate the corn yield potential for their situation. For example if you farm near McCook and will be planting a growing degree day hybrid of 2800 on April 22 and estimate your field potential at 220 bu/ac you should plant the number of seeds which will give you a population at maturity of 30,000. For example, if you use their recommendation, divide 30,000 by 0.94 and you would seed 31,900.

Bob Klein
Extension Cropping Systems Specialist

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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