A roller coaster season

Like most years for Iowa farmers, 2006 was a weather roller coaster ride. The graph shows the weekly departure from 30-year average degree day accumulations from May through September. One way to read the chart is to consider a 1- to 3-week time period and look at the slope of a line at that time. If it was warmer than normal, the line rises; if cooler than normal, the line falls; and if the weather is at the average, it will neither rise nor fall.

2006 Degree Day Departures by Iowa Crop Reporting District
From 30-year averages, 1970-2000.

The first quick observation is that from about July 3 to July 17, northwest Iowa (district 1) was warmer than the rest of Iowa (relative to normal). That said, the pattern of weather through time there was like the rest of Iowa.

Although Iowa weather was far from ideal, we did generally dodge a few bullets during key crop developmental periods in 2006. We entered the growing season with reasonably good crop available moisture, due to good rains in the late winter and spring. Iowa experienced average to above average rainfall and cooler-than-average temperatures statewide the first three weeks of May, which sometimes delayed germination. However, around the last week of May, considerably warmer-than-normal weather got crops up and growing in most areas. Although May, June, and July were exceedingly dry statewide, crops progressed well, relying largely on soil moisture reserves. June and July temperatures were nearly normal. Reasonably moderate weather during pollination helped crops handle the moisture stress, but unusually hot weather (mid-July to mid-August) followed during early grain fill that stressed crops and hindered development. By about mid-August, temperatures cooled and were accompanied by the return of rains, allowing for some recovery in grain production, particularly soybeans (see graph on the back page).

We are now reaching physiological maturity. Individual conditions, and therefore yields, could vary considerably from field to field because of local rainfall intensity patterns, differing varietal abilities to withstand weather stress, and cultural practices, including planting date, cropland tillage and residue cover, and other factors that affect moisture availability. Documenting the season-long conditions at the field and how they affect yield and grain quality can provide valuable management information for future crop season management.

2006 Rainfall by Crop Reporting District
Monthly departure from 30-year averages.

This article originally appeared on pages 239-240 of the IC-496(24) -- September 18, 2006 issue.

Updated 09/20/2006 - 9:59am