2005 Year in Review

How Will Weather Affect This Year's Crop Yields?

Source: Robert W. Frazee, Extension Educator, Natural Resources Management, rfrazee@uiuc.edu

With each passing day of prolonged heat and moisture stress, farmers throughout Illinois are becoming increasingly concerned about how this year's weather will affect their corn and soybean yields, reports Bob Frazee, University of Illinois Natural Resources Educator.

The effect of moisture stress on corn at various growth stages has been studied by University of Illinois Agronomists. Generally, university research has found that corn wilting from moisture stress over a 4-day period caused a 10 percent yield reduction up until two weeks before tasselling. Stress prior to pollination can also reduce the leaf area and potential ear size.

In 2005, most cornfields in central and northern Illinois will be pollinating during the July 5 through July 15 time period. The periods when weather stresses have their greatest effect on corn growth are associated with the length of the flowering period. Corn plants flower over a relatively short period with pollen shed lasting only 5 to 8 days. Frazee reports that university research shows that weather stresses in corn cause the greatest yield reduction when they occur during the two-week period before and the two-week period after pollination. During this period, he emphasizes that it is critical that the silks on the ear emerge in time to catch the shedding pollen. Severe stress during pollination can cause yield reductions of over 50 percent.

During the later stages of maturity, corn yields were reduced, but to a lesser degree than at the end of pollination–up to 40 percent during soft dough, then becoming less significant as the corn matured. Stress after pollination may cause kernel abortion and reduced kernel size.

In contrast to corn, Frazee reports that soybeans have a longer flowering period that generally lasts from 25 to 40 days. Thus, weather stress during soybean flowering is less detrimental to grain yield for soybeans than for corn. The fact that from 25 to 75 percent of soybean flowers normally abort also indicates that short-term stress during flowering is of less importance to the total number of grains produced. According to Frazee, soybean grain yield is reduced most when weather stresses occur during late pod set and early grain fill. Stresses at this time can reduce pod number and weight per seed. Thus the critical time for weather stress in soybeans generally occurs about two weeks later than in corn.

by  Editor, theCity1.com
July 19, 2005