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Illinois Corn and Soybeans in Good Shape So Far

Little yield potential has been lost

Growing season weather in the three I states—Illinois, Iowa, and Indiana—can make or break the U.S. corn and soybean crops (and ultimately, prices, too.) 

So far in Illinois, corn and soybeans look good with little yield potential lost—so far, says 

Emerson Nafziger, University of Illinois Extension agronomist,  says the next few weeks will spell the difference between average and very good crops.

Here’s his take on Illinois crop conditions.

The corn is growing well, fueled by warm temperatures.

Growing degree day (GDD) accumulations since May 1 are running from 150 above average in northern Illinois to about 250 GDD above average in the rest of Illinois.

With GDD accumulations of 900 to 1,000 since May 1, corn planted in early May is at V10 to V14, 30 to 60 inches tall. This corn only needs 350 to 450 more GDDs to tassel and silking. With daily accumulations at about 25 GDD, much of the crop will be showing tassels and silks by the end of June and first days of July.

June 10 crop conditions as of June 10 were 83% good + excellent, one of the highest early-season ratings we’ve ever had. In most fields, the crop looks outstanding, with probably the best stands we’ve ever had. In most cases, crop canopy development and color is excellent.

It’s not all roses, though.

In some areas, afternoon leaf curling is occurring. This indicates that the water supply in the soil is not high enough to sustain maximum rates of photosynthesis now.

Much rain over the past month has been from thunderstorms, rather than broad movement of fronts. As a result, its distribution has been uneven. During the first half of June, rainfall ranged from less than one-half inch in parts of western and southwestern Illinois, to more than six inches in southeastern Illinois. 

Even in those areas showing average or above-average rainfall, places exist where the storms missed and where soil water is starting to run short. The U.S. drought monitor shows “abnormally dry” conditions in several western Illinois counties, and in a small pocket in northeastern Illinois.

Normal to below-normal temperatures will be needed later for optimum kernel set. 

While the well-watered areas with deep soils have current sufficient soil water to get the crop through pollination, normal to below-normal temperatures will assure that the crop has high potential to set the kernel numbers needed for high yields. In areas where plants are showing stress in the afternoon now, we expect that this will set in a little earlier, and last a little longer, each day temperatures remain high with no rainfall. 

Canopy development is good so far, but….

A good canopy also means faster water usage, and a crop that’s head-high has a “crop coefficient” (the proportion of evaporation that the crop takes up) of about 0.7. This value reaches a maximum of about 0.8 at full crop canopy.

That means that if evaporation (also called “potential evapotranspiration” or PET) on a warm, sunny day is 0.25 inches – PET has been high as 0.3 inches on the warmest days in Illinois in recent weeks – the crop takes up 0.25 x 0.7 = 0.18 inches of water. Our best soils can store as much as 10 to 12 inches of plant-available water in the top three feet. At field capacity, the water supply can last six weeks or more without rainfall. 

That’s under ideal conditions, though. Corn will often show stress effects before the soil water is completely depleted. It’s been dry enough in parts of Illinois that the soil water supply is not sufficient to keep the crop well-supplied now.

As pollination approaches, the effect of water stress on the crop will increase.

If it rained everywhere today, the crop could probably recover its full yield potential in most fields. But if leaf rolling starts by noon, the crop is producing less than half the normal amount of sugars through photosynthesis on that day, and the closer the crop gets to pollination the larger the effect of lost sugars will be. Today’s hybrids are bred to produce silks, pollen, and some fertilized kernels under stress conditions, but if it stays dry over the next weeks where the crop is already showing stress, kernel numbers will be lowered. Lower kernel numbers mean lower yield potential.

Corn plants that develop under high temperatures and with plenty of water tend to be taller than usual. In areas where the crop has been showing stress symptoms in the past week or two, though, we can expect plants to end up shorter than normal. Any water stress during rapid stem elongation – between V8 and tasseling – results in less elongation of cells in expanding internodes. This results in shortened internodes and plants. 

As we saw in 2017, shorter plants can still yield well. However, this requires adequate water by a week or so before tasseling to assure that the pollination process can proceed normally.

Dry weather has its benefits.

It encourages good root system development, a good supply of soil nitrogen, and little disease development. Dark green leaf color shows that the N supply has been adequate. Soils that have not stayed wet following rain (except in low-lying areas) have little potential for N loss. Some rains have been so intense that much of the water ran off. The dry period before the rain meant that the soils could absorb several inches of water before becoming saturated. 

Corn that is or has endured standing water will have damaged roots and some denitrification. This could potentially incur considerable yield loss in those areas. Fortunately, this area is not as large in size as it’s been in some recent years.

Good news—you likely can save your money for supplemental N.

Those who applied a normal amount of nitrogen (N) early with the idea that they’d come back to apply more if the yield potential looks good can skip the additional application this year. If leaves are dark green now, it’s unlikely to run out of N. Our N-tracking results from this spring confirm what the crop is telling us – that it has plenty of N. 

Soybeans are looking good, too. 

Illinois soybeans in mid-June have the same high crop condition rating as the corn crop. Stands are good in most fields, and plants have begun to develop rapidly, after the usual lag that we often see from application of certain herbicides. 

In a planting date study we have here at Urbana, early varieties planted on April 25 are at V6-V7 and 15-18 inches tall, with many flowers. Canopy health is good. Growth so far has been good even in dry areas, as small soybean plants use water sparsely. Thus, more water remains in the soil.

Early-planted soybeans have flowers before the longest day of the year—June 21—and also when temperatures are warm. The appearance of flowers requires a certain night length.  and if it takes 10 days after the longest day (June 21) to reach that night length, then that night length also occurs 10 days before June 21. 

However, if plants aren’t past stage V3 or if nights are relatively cool, soybean plants won’t flower before the summer solstice. Even when they do flower in mid-June, limited numbers of flowers might turn into pods. We will need a lot of flowers appearing after June 21 along with good growing conditions in order to set the number of pods needed for high yields.

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