Dryland Corn Population Decisions

Choose seeding rate based on average, local rainfall.

Dryland corn growers are faced with the question, "How many seeds should I plant per acre?" Plant population choice is a critical decision because it affects eventual grain yield potential, and because corn seed costs are a relatively large component of the overall production budget.

Corn yield potential is primarily a function of July and August rainfall (Fig. 2). Each 1" of rainfall received between 15 July and 25 August increases corn yield by 7.5 bu/acre (Nielsen et al., 1996). Stored soil water is a "bank" the corn crop draws from to keep growing between rainfall events. The "water bank" remains important throughout the critical reproductive stage that occurs in July and August, but stored soil water is never sufficient to produce a crop. The critical 15 July - 25 August rainfall determines yield potential. Each grower can estimate their long-term yield potential by using the rainfall records from the weather station nearest their farm (Click on Data Access on the Colorado Climate Center webpage at http://climate.atmos.colostate.edu/). Yield potential will influence the corn population decision.

Data in Figure 3 indicate that 12,000 to 16,000 plants/acre maximized corn grain yield across a wide range of growing season rainfall levels in eastern Colorado (Fithian, 1992). These data provide insight as to what will happen if the grower plants a high population, say 16,000 plants/acre, and the growing season rainfall is dryer than expected. Note that, in the growing season, with only 6 inches of rainfall, the plant populations above 12,000 plants/acre did not affect yields either positively or negatively. This indicates that the grower can plant populations adequate for their expected yield potential and not be penalized if less than average rainfall is received. To maximize long-term profits it is important to plant populations that are adequate for the expected average year, and not for the possible low rainfall year. Dryland farmers maximize their profits by planting a plant population that can take advantage of the higher rainfall years when they occur.

References:
Fithian, W. 1992. Dryland yield book. Pioneer Hi-bred International Inc. Plains Sales Area.
Nielsen, D., G. Peterson, R. Anderson, V. Ferreira, W. Shawcroft, and K. Remington. 1996. Estimating corn yields from precipitation records. Cons. Tillage Fact Sheet #2-96. USDA-ARS. Akron, CO.

Gary Peterson, Professor,
Soil and Crop Sciences