Ag Weather Forum

Yield Questions With Iowa Dryness

Bryce Anderson
By  Bryce Anderson , DTN Senior Ag Meteorologist
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More than half of Iowa is in some phase of dryness or drought. That includes all or parts of 21 counties in severe drought. (National Drought Mitigation Center graphic)

Dryness keeps expanding in Iowa. The U.S. Drought Monitor as of July 28, 2020 shows close to two-thirds -- almost 63% -- of the state in some phase of dryness, at least D0 or abnormally dry. To further refine the situation, about a third of the state -- 33% -- is in at least D1 or moderate drought; and 13% of the state is in D2 or severe drought. That area in severe drought D2 includes all or part of 21 counties in the western half of the state.

In the Drought Monitor class definition, here's what happens with these categories:

D0 -- Corn shows drought stress; soil is dry.

D1 -- Soybeans abort pods; corn test weights are struggling; grasses are brown; more grass fires occur; burn bans are issued; pond levels decline.

D2 -- Dryland corn has extremely low yields; commodity shortages are noted; livestock is stressed; fire danger is high; fewer mosquitoes are observed; surface water levels are low; algae blooms increase; voluntary water conservation is requested.

From a crop production standpoint, some high-production land is getting hit by this dryness. Most of the 21 counties affected by severe drought are in the West Central crop reporting district, which was the top producing district for corn in all of Iowa in 2019 with 420 million bushels (statistics from USDA NASS). All of the top five counties for total corn production are affected by dryness or drought: Kossuth, Plymouth, Pottawattamie, Crawford and Woodbury. Dryness is hitting the top five yield counties also: Crawford (234.7 bushels per acre in 2019); Linn; Marshall; Sac; and Carroll, all with yields of more than 219 bpa in 2019.

The 21 counties in severe drought accounted for 26% of the total Iowa corn output in 2019 at an estimated 680.0 million bushels. That total amounted to an estimated 5% of the U.S. total 13.7 billion bushel corn crop.

Dennis Todey, director of the USDA Climate Hub in Ames, Iowa described the situation this way in an email to DTN.

"Corn is pretty bad in a chunk of that area. Soybeans are showing some issues too already. Grasses and forage cuttings are not very good in 2nd/3rd cuttings of the year. There is definite corn yield loss and we have lost a little in beans.

"The interesting situation is that the driest area of the state has shifted a little over time. Southwest was the worst early on. There has been a shift a little north and east to the current D2 big blob and now a little more in central Iowa. Marshall County is running about the driest in the state now," said Todey.

A look at precipitation totals for the state since Jan. 1 shows that the western and central portions of the state have had mostly 50% below normal precipitation. The eastern one-third of Iowa has taken in from 10 to 50% above normal, much of that from the rare occurrence of tropical system-related rainfall in June when Tropical Storm Cristobal traversed the eastern third of the state from south to north.

Dryness continues in the forecast for these parched counties. DTN precipitation forecasts through Aug. 7 call for no more than one-quarter inch (6 millimeters) total precipitation in the driest areas of western and central Iowa. That's a long way from easing the drought situation. This extensive dryness also perhaps calls into question whether the impact on Iowa crops may be enough to nudge U.S. 2020 yields away from the prospect of record levels.

Bryce Anderson can be reached at bryce.anderson@dtn.com

Follow him on Twitter @BAndersonDTN

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