Ag Weather Forum

In light of last week's USDA Ag Outlook Forum discussions saying that dry soils in winter were not that meaningful relative to corn yield the following season, I thought it was worth re-running a blog entry from early January on the subject of "Low Soil Moisture And Yield Potential." Here it is.

With all the concern about drought -- even in areas that have received more moisture in the past couple months, there is a fair amount of worry about what that means for crop performance in 2013. To get some educated views on that topic, I recently sent a note to several agronomists at Midwest land grant universities with the following questions:

"Considering that it appears that the Palmer Drought Index for November was in the same category for dryness as that of 1934 -- do you have an opinion on what this says regarding corn's yield potential for 2013 -- and is it true that corn's water needs during the pollination period are only half supplied by normal summer rainfall with the other 50% coming from soil moisture reserves?"

I received a couple replies and they are posted below. The comments are maybe a little long, but I know that many of you like the details so they have not been edited. --BA

First, from Emerson Nafziger, University of Illinois--

"I know that the western Corn Belt has been very dry over the past 3 or 4 months, unlike the eastern CB, where we've had close to normal rainfall since late August. Even with maybe 15 inches of rainfall here in eastern Illinois, though, people report very little moisture when they dig deep, and no tiles lines are running.

So there is concern about soil's being dry now, though I don't know if the Palmer Drought Index is a good indicator of how much water is stored in the soil. If we get half to 2/3rds of normal precip from now through March, there should be enough water to fully recharge the soil from the drying out last season. It's quite unusual not to have full soil moisture recharge in Illinois; we last saw this in a few areas in 1989. But we'll be watching it closely. Of course, as we saw this year, even with full recharge by spring it still has to rain to make corn yield.

To answer your question about water use: it depends a great deal on where you are in the Corn Belt, but corn crop water use during the month of July here would typically be about 6 inches, and rainfall averages about 4 inches. Season-long, Our better soils can hold about 10 to 12 inches of water available to the crop, and seasonal rainfall (May through August) averages about 4 inches per month, so 16 inches or so. Water use by a 200-bushel corn crop is about 22 inches, so between the soil and rainfall there is little deviancy most year. In a year like 2012, where rainfall in June and July totaled less than 3 inches in many places, along with very high July temperatures (rapid water use), the crop couldn't extract enough water (fast enough) to make pollination work, or to work well, and kernel set was very poor.

In un-irrigated areas of Kansas and Nebraska, water use (evaporation) rates are higher than here, and rainfall is less on average, so yield loss to water deficiency is more common. In a year like 2012, soil water would have been depleted fairly early, resulting in pollination problems and low yields."

And, from Bob Nielsen at Purdue University--

"As you probably know, corn requires between 20 and 25 inches of water to produce a crop. That comes from some combination of soil reserves + rainfall + irrigation.

Soils vary in how much water they can store per foot and, of course, for effective rooting depth. Most of our non-sand soils store between 1.5 and 2 inches of water per foot of soil. If the effective rooting depth was 3 feet, that translates to 4.5 to 6 inches of water holding capability. If 4 feet, then upwards of 8 inches of water holding capability. Sandier soils may store only 3/4 to 1.25 inch per foot.

Any way you calculate it, most soils cannot supply as much as half what the crop needs. So, timing of rainfall or irrigation during the entire season is crucial.

I learned a long time ago not to try to predict a corn crop this far in advance. So all I will say is that going into a growing season with excessively dry soil reserves is obviously not desirable for achieving high yields."

Bryce

(CZ/SK)

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