We worried our way through the cool month of April, with 32 percent of corn and only 7 percent of soybean acres planted by April 29, and nothing emerged. During the first two weeks of May, the weather was warmer and drier than normal, and adding together corn and soybeans, Illinois farmers planted more than a million acres for each of the 10.3 “days suitable for fieldwork” between April 29 and May 13.
By May 13, 90 percent of the corn was planted and 63 percent had emerged; the numbers for soybean were 66 percent planted and 24 percent. The soybean stands I’ve seen so far are good, and corn stands are truly outstanding – among the best we’ve seen in Illinois. Warm temperatures brought the crop up quickly and uniformly, and one would have needed a stopwatch to find differences in emergence time between plants down the row this year. If, as some like to claim, uniform emergence is the key to high yields, we’re in for a great year.
Cool soils dry slowly, and soils did not have enough time to dry out very much between tillage and planting this year, even with warm and windy conditions. This helped fields emerge quickly and uniformly despite lack of rain. The once-upon-a-time worry that soils will dry out fast enough to delay emergence is almost a thing of the past due to fewer tillage trips, less time between tillage and planting, and better seed placement by today’s planters.
Temperatures have been above average every day in May so far, with an average of more than 18 GDD per day accumulating in Illinois. The average under normal temperatures is only about 12 GDD per day for the first half of May. So corn planted on May 1, that would normally take 10-11 days to accumulate the 115 or so GDD needed to emerge, took less than a week to emerge this year. That temperature trend continues, and we’re on track to reach about 600 GDD for the month of May. That will have most corn fields at the V5-V6 stage by the end of May, ready to begin rapid growth. If June brings the normal 650 to 700 GDD, we’ll see tassels and silks in many fields before the July 4 fireworks.
Some might have noticed that the 5-year averages used as the basis for comparing this year’s planting and crop development progress seem to have changed since last year. That’s because the past five years (2013-17) no longer include 2012, which was the year with the earliest planting on record, followed by rapid crop development, but also drought and low yields. So we can expect to be ahead of average a little more often over the next few years.
Warm weather after planting can increase the potential for so-called “high-crown syndrome” in corn. We think this comes from having the coleoptile (the pointed structure we see when the corn is “spiking through”) growing so quickly that it grows above the soil surface before the coleoptile gets the signal – from sunlight striking its tip – to stop growing. It might even make a difference if emergence begins near the end of the day and the night is warm, in which case the tip of the coleoptile might be a half inch or more above the soil surface by the time sunlight hits it the next morning.
When the coleoptile stops growing, the crown (the base of the stem) establishes about an inch below the tip of the coleoptile. Normally, the tip of the coleoptile may be an eighth to a quarter of an inch above the soil surface, and the crown sets at least three-quarters of an inch below the soil surface. If the coleoptile tip is a half inch above the soil surface instead, the crown may set only a half inch deep – the “high-crown syndrome.” I have not heard of any of this in 2018 so far, but the temperatures have been favorable for its development, and it’s not something we see unless we look for it.
The major concern when the crown is shallow is the possibility that the nodal roots, which originate at the crown, might be unable to grow out into the bulk soil soon enough to provide water, nutrients, and support for plant growth. If the surface soil is very dry and loose, or a no-till furrow remains open with dry, hard surfaces, nodal roots can struggle, or even fail entirely, to grow; the result can be “rootless” corn. Plants may stay alive to stage V4 or V5 with just the seminal root system that grows from the seed at germination, but they need a nodal root system – the “permanent” root system – in order to continue to grow. In the worst cases, plants without nodal roots fall over and can detach from their roots and die.
I don’t want to raise an alarm about the potential for high crown placement this year – we’ve more often anticipated this problem than we’ve actually seen it. Enough rain that comes early enough to get the nodal roots to take hold and start growing will often mean no noticeable yield loss from this. Short of replanting, which no one wants to (or probably should) consider with a near-perfect stand, rain to get the roots growing is the only cure. Today’s fast-growing hybrids can do the rest.
One question I’ve heard a few times in recent weeks is whether there’s any need to worry about how much nitrogen remains in the soil as the crop approaches the stage of rapid N uptake. With below-normal rainfall in April and so far in May, and below-normal temperatures in April, and no extended winter thaw, we think that N that was properly applied anytime since last fall should be present. The only wet period we’ve really had in Illinois was odd mid-February system that dropped 5 inches or more in places, but that was during a time of cool soils and water did not stand very long.
Samples taken over recent weeks confirm that the applied N is still there, and also hint that mineralization began early, as we’d expect given the conditions this year. According to data from the WARM network of the Illinois State Water Survey, current soil moisture at the 4-inch depth is in the mid-20s (% of soil that’s water – less that 20% is starting to get dry, more than 35% is wet) over much of the state except for the northern and southern ends of Illinois, which are wet. Soil temperatures at 4 inches are in the upper 60s to lower 70s, well above normal for mid-May.
An early start to mineralization and lack of saturated soils are indicators that roots starting to develop on corn seedlings should get early (and easy) access to N in the soil. There will still be some lag in leaf color as growth gets underway, but if the sun shines and temperatures stay warm, we should see the leaves start to darken by the time plants have 4 or 5 leaf collars visible. And when the supply of N from the soil is good, that usually means good root growth and good supplies of other nutrients as well.
Source: Emerson Nafziger, University of Illinois