By Dr. Harold Willis
When planting corn, it’s important to understand best practices for your highest yields.
Where and How to Plant Corn
There are many factors that govern optimal population and row width, ignoring the obvious one of the type of machinery you own. Very important are moisture and nutrients, for high population corn needs high fertility soil and adequate moisture. In general, with average rainfall, you can plant higher populations in the northern and eastern U.S. than in the southern and western areas of the corn belt, unless you can irrigate.
If moisture and nutrients are adequate, narrower rows and higher populations give higher yields. Drilling, with accurate within-row spacing, gives better yields than hill-dropping or check-planting. Higher populations can be planted if corn is grown for silage or fodder than for grain. Average populations are about 17–18,000 per acre, low populations are about 12,000 per acre, and high populations can run up to 25–30,000 per acre. Typically, only about 85% of planted kernels reach maturity, so here is a table giving kernels per acre to plant and kernel spacing for drilled corn (adapted from R. J. Delorit, L. J. Greub, & H. L. Ahlgren, Crop Production, 4th ed., 1974, p. 105):
Although higher populations give higher yields under ideal conditions, if there are stresses from adverse weather or if the soil runs out of readily available nutrients, yield and test weight will be reduced, as will ear size, leaf area, number of ears, and protein and oil content. Silking will be delayed, leading to poor pollination. Lodging, stalk rot, corn borer, and other problems will be increased.
Nutrient deficiency throughout the growing season can often be corrected by side dressing and/or foliar feeding. But considering the unpredictability of the weather, it may be best to avoid the temptation to plant very high populations and risk getting a poor crop.
When to Plant Corn
In general, earlier planting produces better yields, but that can be carried too far. Everyone wants to be “first on their block” to get their corn planted, and often the soil is simply too cold for germination, or a late cold spell injures seedlings or slows growth. Corn will hardly germinate below 50°F soil temperature, and the best temperature is about 68°. Tests have shown that at 50–55°, corn takes 18–20 days to emerge; at 60–65° it takes 8–10 days; while at 70° it only takes 5–6 days.
Best seedling growth occurs at 86°F. It is best to check the soil temperature at a two-inch depth to be sure the soil is warm enough. Checking in the morning will give a truer reading, since the soil temperature at that depth may rise 5–15 degrees on a sunny day. When soil temperatures reach about 55–59° for several days — plant. Planting should not be delayed if the soil is warm enough, so that the corn can make its vegetative growth before hot, dry weather, which can interfere with silking and tasseling. However, later planted corn, especially open pollinated varieties, can often catch up with early planted hybrids if soil fertility is high enough.
Seed should be planted deeper (2–4 inches) in light or lumpy soil, and shallower (11/2–3 inches) in heavy soils or a good seed bed. Proper moisture at planting depth is most important, then comes temperature. In dry soils, you may have to plant as deep as 3–4 inches in clay or 5 inches in sand to have enough moisture. For very early planting, plant 1/2 to 1 inch shallower than normal (if moisture is adequate) to avoid cold temperature.
Source: How to Grow Top Quality Corn