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You Planted Corn When? How Early Is Too Early

Emerson Nafziger
Professor of Crop Production
Department of Crop Sciences
(217) 333-4424; ednaf@illinois.edu
Emerson Nafziger

In the year 2000, as in 1999 and a small number of years in the past two decades, many areas of Illinois had weather in March and April that was warm and dry enough to result in soils ready to plant by late March or early April. In 2000, planting was possible even in early March in some places. Some producers in Illinois took advantage of this unusually warm and dry spell; we heard reports of planting as early as the first week of March.

How unusual is the chance to plant in early March? In 2000, the average high temperature for the first 10 days of March was close to 60 degrees at Urbana, and we accumulated about 50 growing degree days (GDD) during that period. Even more unusual was the 62 GDD during the last nine days of February this year. Normally, we would not get any GDD accumulation until about the last week of March. Rainfall was also very low during this period, and soils were dry and warm enough (around 50° F) to plant by the second week of March.

In order to see how planting date in such an unusual spring might affect the corn crop, we made single-strip plantings on March 10, March 23, April 6, April 26, and May 12. It snowed 2 inches on March 11, and temperatures immediately dropped to more normal levels, with night temperatures below freezing on seven of the first 10 days after this planting, including a low of 16° F on March 12. Total March rainfall was only 1.77 inches. Except for a wet period mid-month, April was drier than normal (2.78 inches of rain), and temperatures were close to normal, with 202 GDD accumulated for the month.

Days to
GDD to
per Acre
March 10 April 13 34 132 26,000
March 23 April 15 23 126 31,200
April 6 April 25 19 112 28,000
April 26 May 4 8 98 28,200
May 12 May 21 9 95 29,300

Many producers took advantage of the favorable weather and planted early-by May 1, about 60 percent of the corn had been planted in Illinois, and by May 7 more than 90 percent had been planted. This much planting by May 7 was attained only once before in Illinois (in 1988) when drought devastated the state's corn crop.

Strips were planted at about 32,000 seeds per acre, using the hybrid Pioneer® 3489. The table below shows what we recorded from these plantings. Because GDD is based on air temperature and emergence is more closely tied to soil temperature, GDD to emergence took progressively fewer GDD as soils warmed, but these observations generally support the prediction that it takes about 110 to 120 GDD to corn emergence.

While the plant stand was slightly lower in the first planting than in later ones, emergence was relatively unaffected by planting date, even though it took more than a month for the earliest planting to emerge and barely more than a week for the two later plantings to emerge. As we have observed before, dry weather after planting tends to preserve seed and seedling health; as long as soils are only cold and not wet at the same time, emergence tends to be very good. The few reports we had of poor stands in Illinois tended to be from plantings made just before the cool, wet weather that occurred in the third week of April.

While this spring is one in which it "worked" to plant just about anytime, what should we expect from very early planting? Figure 1 shows the results of a planting date study that we conducted in Northern Illinois in the late 1980s. In that work, we found that planting in early or mid-April tended to reduce yield compared to planting in late April. This yield loss was rather subtle-it was not due to plant populations (plots were thinned to exact stands) or observable damage from weather or pests. Rather, we believe that this yield loss was due to the fact that plants and leaves tend to be slightly smaller when planting occurs very early, probably because early growth tends to take place when temperatures are lower than optimum. Slightly smaller leaves and shorter plants may affect the ability of the plant to intercept sunlight later in the season, thus lowering yield. Lower temperatures during early vegetative growth (six- or seven-leaf stage) may also affect the size of the developing ear.

Planting date response in Northern Illinois

Figure 1. Planting date response in Northern Illinois.

Does that fact that very early planting has "worked" more often than not in recent years mean that risks we generally associate with this practice are decreasing? Genetics, seed production and quality control, and treatments all have improved the ability of planted corn seeds to emerge and produce healthy plants. But we believe that very early planting still brings some risks, and though we have limited experience, we would have to consider March planting in Illinois more likely to fail than to succeed. It does appear, though, that in central Illinois, there may be little reason to delay planting until later in April if the soil early in April is in good condition to plant.

It makes little sense to "mud in" corn in April, since wet planting conditions combined with cool soils usually lead to stand problems. But we do expect soil temperatures to rise in April, so we may not need to wait to plant as long as soils are dry enough. (In order to get dry enough, there usually needs to be some warming temperatures as well.) As Figure 1 indicates, we may see slightly lower yields from planting in early April, but many producers will trade that for the ability to finish planting early. And, in case the weather doesn't cooperate, replanting a field that was planted very early usually can be done in time to lose little if any yield from the planting delay.

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