Optimum Corn Population. Corn population should be between 29,000 and 31,000 plants per acre at harvest to produce the maximum grain yield. Grain yield is lower for populations below this. Table 1 gives the relationship between yield and harvest plant population. To achieve this harvest population, I suggest increasing the seeding rate by 15% when corn is planted prior to May 1 and 10% when corn is planted after May 1. Soil temperatures are lower in late April and there is a greater risk that some kernels nay not successfully germinate and emerge so one should increase the seeding rate to obtain the desired final stand to produce the maximum grain yield.

Table 1. Relationship between harvest population and corn grain yield.

Economic Optimum Plant Population. Seed costs have continued to increase especially with technology fees and one might ask if this recommended population is economically sound. That is, will the increase in yield pay the extra seed cost to achieve a final stand of 30,000 plants per acre (ppa). The increase in yield with each increase in plant population becomes smaller as the optimum population of 30,000 ppa is reached (Table 1). So if the 2% yield increase for 28,000 versus 30,000 ppa pays for the extra seed cost, then the higher population is an economically sound investment. Yield level, seed corn price and grain selling price are factors in the economic analysis. Table 2 gives the extra return in dollars per acre for the 2% extra yield increase for a stand of 30,000 versus 28,000 ppa for various yield levels and seed corn prices.

At 100 bushels per acre one can pay up to $130 per bag of seed and have a slight return for the higher plant population with a grain selling price of $2 per bushel (Table 2). At 120 and higher yield levels, there is a positive return for the higher plant population for seed costs of as high as $150 per bag. Table 2 shows the obvious – the economics of high plant populations (one makes more money) are better at low seed prices and high yields at any grain selling price.

The value of the extra yield is greater than the extra seeding cost for increasing the plant population up to 30,000 ppa at grain prices of $2/bu and higher. Therefore, one doesn’t need to evaluate the economics of plant population changes below the 28,000 level because the increases in yield for incremental population changes below 28,000 ppa are greater than the 2% we just evaluated for various seed corn prices and yield levels.

The economics of higher plant populations are even better at any yield level and seed corn price as the grain-selling price goes up. Returns are given in Table 3 for yield levels and seed prices for a grain-selling price of $2.50 per bushel.

Summary. While one should strive to minimize seeding cost, there are other more important factors to consider when buying seed corn. They include yield potential, maturity, moisture at harvest, resistance to diseases, insects, and herbicides, stalk quality, and other plant traits. Seed cost should be the last consideration after hybrids are chosen based on these performance characteristics.

Table 2. Returns ($/A) for the 2% Higher Yield For 30,000 Compared With 28,000 Plants Per Acre For Various Seed Corn Prices and Grain Yield Levels and Grain Selling Price of $2 Per Bushel.

Table 3. Returns ($/A) for the 2% Higher Yield For 30,000 Compared With 28,000 Plants Per Acre For Various Seed Corn Prices and Grain Yield Levels and Grain Selling Price of $2.50 Per Bushel.