MANHATTAN, KANSAS, U.S. — A bout of temperatures in the high 90s and low 100s descended on much of Kansas the week of July 8, with heat advisories from the National Weather Service covering all but the most western areas of the state. 

At this point, the Kansas corn crop is already exhibiting signs of “mild distress,” said Ignicio Ciampitti, crop production and crop system specialist in the agronomy department at Kansas State University. The key stage of pollination is expected to start in mid-July, when excessive heat on dry soil can inhibit the process and create ears with damaged kernels. 

Despite some indications of problems, Dr. Ciampitti said, “I am seeing really good corn crops” in different areas of the state. 

“What will be really critical between now and the end of the season is how much rain will we be able to get in the next few weeks,” he said. 

He said the need for additional rain along with the summer heat underscores the potential damage inherent in “the combination of high heat with low soil moisture.” 

As of July 7, only about 12% of the Kansas crop had reached the silking stage, down from a 37% five-year average, the U.S. Department of Agriculture (USDA) said in its July 8 Crop Progress report. That means an overwhelming majority of silking this year will occur when temperatures are likely to be quite high and rainfall may be sparse. 

Dr. Ciampitti said he has seen signs in central and western Kansas of effects of soil moisture deficits — leaf rolling, poor root development, unusually small specimens and plants where the tassels are visible but there is little development of the ear and silk — a lack of “synchrony” between the male and female parts of the plant. He defined this year’s window for pollination as, on average, the time period from the middle to the end of July. During that time, temperatures in the mid to high 90s, especially with little night-time cooling, for as little as five consecutive days, can start to erode yields, he said. 

“Everything depends on the soil moisture and root system,” Dr. Ciampitti said, adding, “If the corn has deep roots, that makes a whole lot of difference. Every day after four or five days of high temperatures, maybe above 95 or 96, without much change at night, we will probably see about 1% of yield lost.” 

On July 8, the USDA’s Kansas field office described average topsoil moisture in the state as 68% very short or short and subsoil moisture as 66% very short or short, with areas west of Wichita bearing the brunt of the dry conditions. Though wheat is the main crop in Kansas, corn is widely grown; irrigation makes successful corn cultivation possible in the state’s High Plains, where yields can be as much as 200 bushels an acre. Dry land corn there is a much riskier proposition, Dr. Ciampitti noted. He said growing corn is economical in Kansas as long as the producer can harvest at least 60 to 70 bushels an acre. Kansas was the tenth largest corn producing state with 379 million bushels (total U.S. crop of 10.78 billion bushels) in 2012, but was as high as sixth with 581 million bushels (U.S. crop of 12.447 billion bushels) in 2010, according to the USDA. 

“We know we will have high temperatures but we also need to see if the temperatures will be accompanied with some kind of rainfall,” Dr. Ciampitti said, acknowledging the near impossibility of predicting accurately when rain will come this July. In the current weather forecasts, “We are not seeing really big thunderstorms. We are seeing isolated thunderstorms.”