Still Cold and Dry: What About Corn Planting?

April 7, 2000
The temperature is dipping below freezing as I write this (April 4), and there has been little rain to relieve soil dryness in many parts of the state. While many corn planters are starting to roll, and some have already finished, others are still holding back, waiting until the calendar, if not the temperature, is a little friendlier. Who's right?

Without doubt, planting corn the first half of April in Illinois is riskier than planting later in the month: the soils are often too cool for germination, and even if they are warm enough, there's a good chance that they will drop back to less than 50F at some point after planting. This is especially true of drier soils, which warm and cool faster than wet soils. If this drop in temperature lasts only a few days, it will probably have little effect on seeds or seedlings. If the cool period is prolonged, microorganisms may attack and even kill emerging seeds or seedlings that are growing slowly or not at all. This problem usually occurs when soils are wet; as we've seen several times in past years, seeds generally survive well in cool soil if the soil stays dry.

The knowledge that seed can survive well in cool but dry soils is an encouragement to start planting. While the weather certainly seems to be following a dry pattern, it can also change rather quickly to a wet pattern, and corn seeds in the soil may not survive well if the soils stay cool. It is probably reasonable, though, to begin planting those fields where the soil is clearly fit to plant.

Pushing to get done by the middle of April is probably not necessary, but recent history indicates that some producers will do this so that they can start planting soybeans, in the belief that soybeans planted early also get off to a better start and produce higher yields. Remember that soybean seeds need more water than corn seeds to germinate and that they don't survive or emerge as well in cool soils as do corn seeds. Also, some soybean seeds had been reported to have lower-than- normal germination, and emergence of such seeds from cool, dry soils may be very slow or may be at very low percentages.

The continued dry weather has also caused many people to consider how they might take steps now to reduce the risk of dryness affecting the crop. While soil moisture storage has increased in many parts of the state with rainfall, many soils are not fully recharged. That is unusual, but many of our deeper soils, even if only two-thirds or three-fourths recharged, hold more water in the rooting zone than do shallow or coarse-textured soils used to grow corn in many parts of the country and the world. And, if we get normal rainfall during the summer months, the lack of full recharge at this point should have little effect on yields.

Are there ways that we can manage to help protect against the continued possibility of dryness? In the most pessimistic scenario, continued lack of measurable precipitation will mean very bleak crop prospects, no matter how we choose to manage. There is probably little that we should consider changing to protect the crop against drought, as a return to a more normal rainfall pattern is likely. Some things that probably should not be done follow:

· Don't try to return corn hybrids already in your shed for ones that are more drought tolerant, unless you have light-textured soils and you carelessly ended up with hybrids that you know to be sensitive to drought. The majority of hybrids on the market were bred to do well under a range of conditions, and they have some ability to withstand dryness without going barren. We don't have many, if any, hybrids sold for use in Illinois that are specifically developed for drought conditions; they simply give up too much yield potential to be practical on all but our sandiest soils. If you made good hybrid choices to begin with, stick with those.

· Don't lower the planted population very much, if at all. It's probably not the year to "go for broke" on the high end of population, but neither is it the time to revert back to populations we were planting 20 years ago. Most of our work shows that yields tend to level off, rather than drop, as populations rise above the optimum. This suggests that the penalty for overplanting for the conditions is mostly the price of the extra seed rather than in loss of yield. On productive soils with yield expectations above 150 bushels per acre, we suggest that harvest populations should be in the upper 20,000 to about 30,000 per acre. This can be decreased for less-productive soils, but establishing less than 24,000 to 25,000 might well limit yields on these soils as well.

· Don't try no-tilling as a way to conserve soil moisture, especially if you don't have experience or equipment to no-till with confidence. Most soils already have ammonia applied, meaning that the planter rows will cross in and out of zones where the soils are dried out, and emergence is likely to be uneven, which can reduce yields. But the most important reason to avoid emergency no-tilling is that no-tilled soils retain capillary connections to the soil surface and hence will sometimes dry out faster in the upper several inches than will tilled soils. This is not to suggest that no-till will necessarily have more problems if it stays dry, but a layer of disturbed soil on the surface does break capillarity and can help to retain water in the soil.

· Don't do that extra tillage pass unless it's absolutely necessary for leveling. Any stirring up of moist soil will expose it to drying air and might easily drop its moisture content below that needed for seeds to germinate.

· Don't plant to moisture if that means planting more than 1 3/4 inches deep. Deeper soils warm more slowly, and, if it happens to rain after planting, it's almost always the deeper-planted seeds that have problems coming up.

· Don't think about switching corn acres to grain sorghum, unless you just signed an amazingly good contract for grain sorghum. With its sensitivity to cool temperature, grain sorghum is seldom a good idea under any circumstances in the northern half of the state. Some grow it successfully in southern Illinois, especially if planting is late in warm soils, but it is a crop that needs warm weather to do well, and it also can suffer serious losses from drought.

· Don't automatically reach for additional seed treatments to add to what the corn seed already has applied. Extra treatments could pay if the soils get wet and stay wet, but we have little reason to expect that to happen at this point.

· Don't rule out the use of starter fertilizer, if you have the equipment and have been considering using it. Starter usually gets plants off to a faster start in cool soils, and this could be a year when that will be beneficial. Placement with the seed is acceptable if the amount of nitrogen plus potassium does not exceed 10 pounds per acre, but, when we see injury from fertilizer, it is usually under dry soil conditions, so do this with caution.

· Don't stop watching the markets: modestly dry weather hurts corn in states other than Illinois and Iowa and allows farmers here to take advantage of weather rallies, which we're likely to see as the dryness persists over much of the Corn Belt.

It's likely that some producers, some with "fingers crossed," will start planting in the next week, while others, particularly in the northern third of the state, will hold off until after the middle of the month. One of these options will probably prove to be the better choice, but at this point we simply don't have the information to guess which that will be. Maybe flipping a coin is as good as any other method at this point, but even if we start, it makes sense to plant in an orderly way and to avoid panic if we're not done by April 20.Emerson Nafziger

Author: Emerson Nafziger