?Sweaty? corn exists, but meteorologist says Gulf moisture brings more humidity

BY BROOKS TAYLOR

Mt. Pleasant News

With just three days remaining in July, most people?s reflections of the month would fall into the hot and humid category.

But is that accurate?

Not necessarily, said Ray Wolf, a meteorologist with the National Weather Service?s (NWS) Quad Cities office.

Wolf said, thus far, temperatures in southeast Iowa rank a degree or two below the normal temperature in July. ?We tend to think it was hot (in July), but statistics don?t necessarily bear that out.?

The NWS does not chart humidity, Wolf said, so he has no idea how this July fared to past Julys. ?Although we don?t keep records of humidity, it seems like this summer was more humid.?

In recent weeks a new term ? ?sweaty corn? ? has appeared in articles. The term actually means evapotranspiration, or the natural process of water evaporating from the plants into the air.

All plants ?sweat,? Wolf said. ?Crops and grass sweat. When there is dew or rain on the plants, water evaporates. Meanwhile, water coming through the roots of a plant is called transpiration. So, when you mix the two together, you have evapotranspiration.?

He said that the greatest amount of evapotranspiration from corn is in July when the plans are reaching maturity and pollinating. For soybeans, the peak evapotranspiration is in August.

Virgil Schmitt, regional Iowa State University Extension crop specialist, agrees with some recently published reports that suggest during the growing season, an acre of corn sweats off 3,000 to 4,000 gallons of water each day. The same report also said that in Iowa, corn puts 49-56 billion gallons of water into the atmosphere each day. That water can add 5-10 degrees to the dew point, which is the measure of the humidity in the air on a hot summer day. Dewpoints in Iowa during July, according to Wolf, were in the upper 70s last week. Anything above 70 is considered oppressive.

Wolf, though, said he doesn?t agree completely with the aforementioned statistics. ?Part of the humidity in the summer is caused by evapotranspiration,? the meteorologist said, ?but the primary moisture source in the summer is from the Gulf of Mexico.?

Schmidt said that every green plant that has roots is pulling water and nutrients through its root system and loses it through its leaves. The water loss increases as crops near maturity, he noted. ?The more leaf area, the more water the plant will lose. A corn plant can use a third of an inch of water per day. Once pollination occurs, the water consumption goes down. The same thing is true for soybeans. The closer they are to maturity, the less water they are consuming and losing.?

Wolf did not have July rainfall statistics for Mt. Pleasant, but said Burlington has received 6.45 inches thus far in July, as of July 24. Normal rainfall in July is 3.34 inches. Last year, Burlington had 6.78 inches of moisture in July.

?It has definitely been on the wetter side this July,? Wolf stated. ?We have been getting more heavy rainfall events during the month.?

He also noted that the El Ninó weather pattern that has gripped the United States since last fall is weakening and a La Niná is a possibility this winter.

?We are kind of in a neutral pattern now,? Wolfe said. He added that a La Niná generally means a cold, dry winter. ?However, that is by no means a guarantee of that type of weather. It is just a part of many factors that impact winter.?