Look at the summer picture as a whole for Indiana and it doesn't look quite so threatening or unusual. Statewide averages do place this past Hoosier summer as only one of nine since 1972 with both above-normal temperatures and below-normal rainfall. You're probably thinking that's not good for crops, and you should be right. In most of the previous eight years, yields went down from August estimate through final yield, as predicted and reported by USDA. In a couple of the years where corn yields went up after August estimates, such as '88, weather damage was already so obvious by the end of July that USDA estimated very low yields in August to begin with.
After you look at the weather data table for the June-August period, you would expect below-average corn yields. Yet most recent USDA estimates look for higher than trend corn yields, with higher yields than the five-year average in all but one crop reporting district- east-central Indiana. Soybeans are a different story, but yields are still respectable, although latest estimates dip below 40 bushels per acre in east-central and the entire southern third of the state.
To find out the reason behind these unusual linkages, you've got to downsize from the big picture and start looking at local conditions, says Ken Scheeringa of the Indiana state climate center, located at the Midwest Regional Weather Service office in West Lafayette. "Averages tend to mask out the extremes both over time and area," he says. "A 3-month average doesn't tell us much about the variability over small time periods, like weeks.
"Not only do averages smooth out time, but also area. What happens over a crop district may be much different than what happens in part of a county somewhere. That's certainly true this year. Things can be much different, and they were!"
That's why Scheeringa believes 'variability' is the bye- word in Indiana for both weather and crop yields this year. Summer thunderstorms traditionally dump more rain in some spots than others. Jim Newman reported on that many times during his tenure at Purdue, and later as an independent ag climatologist. But what occurred this past season perhaps goes well beyond normal variability, even in Indiana summers.
A glance at July only and August only weather tables begin to paint a different picture, and explain why corn yields held up, but why soybean yields likely won't, at least in southern Indiana. July was actually below-normal in temperature, on average, across all districts. On the other hand, August was above normal, by as much as 6 degrees above normal for the month, in southwest Indiana. It's common knowledge that July is the critical period for corn pollination and ear development. August is crucial to soybean reproduction and pod fill.
Northern Indiana began receiving lots of rain in August. According to the table, even district 5, in central Indiana, was above normal. But in truth, part of the district above Indianapolis received considerable rainfall, but counties south, including Johnson, Shelby and Bartholomew, for the most part saw very little rain.
Variability! What else can you say?