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North America: Time to Pollinate - Where's the Rain?

North America: Time to Pollinate - Where's the Rain?

28 June 2012

ANALYSIS - Most parts of the US Corn Belt are significantly below the moisture level needed to ensure kernel development, and there's no near-term relief in sight, writes Sarah Mikesell, TheCropSite senior editor.

Drew Lerner, meteorologist and president of World Weather, Inc., told attendees of the Allendale Inc Ag Leader monthly webinar series that over the last several weeks we've seen nothing but problems across the Midwest due to the steady decline in soil moisture across parts of the region. The lower Midwest has been impacted most by the dryness, and expectations are for very low precipitation at least for a little while longer.


A very large portion of the US has been drier than normal amid 2 years in a La Nina cycle. Graphic courtesy of Drew Lerner, World Weather Inc.

"Over the past 30 days, we have seen rain totals across the heart of the Midwest running roughly about half of normal," Lerner said. "The moisture deficits that have crept up have been very impressive. We have moisture deficits that run from 2.5 to upwards of 6 inches, and there are a few locations that have managed to see even higher deficits."

Precipitation across the Midwest has not been significant recently. Rain amounts have been about one-half inch to 2 inches over the last 30 days.

"While that may sound OK, with the temperatures running in the 80s and 90s and occasionally in the 70s, these temps are by far too warm for the limited rainfall we've seen," he said. "That's why we have a big problem in Illinois, Indiana and parts of Missouri. We should be in the four to five inch range and in some areas we've only seen one-half inch, so that's a serious situation."

The Topsoil and Subsoil Situation


Top: Limited to dry topsoil conditions span much of the Corn Belt. Bottom: Yellow and orange areas in southeastern Illinois and Indiana and western Kentucky, show marginal and limited subsoil moisture. Graphic courtesy and © Drew Lerner, World Weather Inc.

Topsoil - that includes the top 18 inches of soil - is critically dry in the northern Delta down to the Tennessee River Basin and then northward into Indiana and part of Illinois. And even more concerning, the subsoil moisture levels are drying up too.

"We are basically out of moisture at the top and subsoil levels in southeastern Illinois, southwestern Indiana and into Kentucky," Lerner noted. "That's where the worst conditions are, but really there is no moisture in the top 18 inches of soil, so these crops are having to reach very deep into the ground to get to the moisture they need going into the reproductive phase."

And he said that's the problem - there isn't enough moisture in the subsoil to carry crops for very long.

"This is different from past years of dryness where we've had soil moisture down deep in the ground," he said. "When it's turned dry, it hasn't been an issue because there's always been moisture available that crops could tap into, but now we are depleting that moisture. As we go into the next few weeks and continue the dry bias, crops are only going to get more and more seriously stressed."

Lerner said not everyone in the Midwest has been suffering from dry conditions, noting Minnesota, Wisconsin and parts of IA have received enough rain to do well over the last 30 days. He expects those areas will continue with moisture for a little while longer, but anticipates that there will be more and more ridge development over the western Corn Belt instead of in the eastern areas and that means the dry bias is going to shift westward.

Can the Corn Pollinate?

Over the next two weeks, everyone's focus is on weather as the Corn Belt prepares for the critical pollination phase. Lerner expects to see some scattered showers across the Midwest during this time, but the odds are fairly good the rain amounts are going to be well below average and warm temperatures will continue as well.

"We will have successful pollination - the moisture will help make sure that the pollen sticks to the silks," he said. "But the problem is going to be in supporting the kernel development afterwards. We've got to have greater moisture in the soil or a regularly occurring amount of rainfall across the Midwest to ensure that kernel development will occur without a problem."

Since we know the soil moisture situation is bleak, the pressure is going to be on regularly occurring rainfall and at the moment Lerner says that's a bit of a long shot.

"We will see scattered showers increase in July - we will not be as absolutely dry as we have been but that really means instead of 25 to 50 per cent of normal rainfall for June, we're probably going to see July run 50 to 75 per cent of normal," he said. "But that's still not going to be good enough for quite a few areas - we are going to be dealing with stress throughout the period. This raises great concern about the production potential across the Corn Belt. We are already sliding down and will continue to see that for a while longer."

July - August Forecast

The outlook data for July and August suggests that the driest area is going to be in the southwest Corn Belt. Nebraska and portions of Iowa, Missouri and Kansas are going to be underneath the ridge quite often in July and August.


Graphic courtesy and © Drew Lerner, World Weather Inc.

In August, Lerner expects some important changes will take place. First, the 18-year cycle suggests a more active weather pattern in July with more frontal boundaries passing through the region and an increasing amount of cooler air over time.

"Second, the next 30 to 60 days could see the development of El Nino," he said. "El Nino will likely put moisture back into the atmosphere and give us a better chance for producing some rain across the Midwest, while at the same time creating a cooler bias in Canada and parts of the northern US Plains states. As that cooler bias evolves in late July and August, this will set the stage for more rainfall across parts of the Midwest."

He said two things to keep in mind - the monsoon season is going to kick in down in the southwestern US bringing moisture up through Mexico into the Rocky Mountain region and eventually across the northern Plains. This will help take the frontal boundaries coming out of Canada and create more rainfall into parts of the Midwest.

"Second - in any summer - it's almost impossible to get the normal amounts of rain to be great enough to raise soil moisture with temperatures near normal," he said. "Evaporation rates are so high in the heart of the summer that it's difficult to make up for moisture deficits."

He said that doesn't mean the Midwest can't have a wetter-than-normal end of the summer, but it would take a tremendous amount of rainfall over the next few weeks to make up the deficits that have occurred over the Midwest. Right now, Lerner says the odds seem stacked against that happening.

Sarah Mikesell, Senior Editor

Sarah Mikesell, Senior Editor



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