You've seen the maps and charts displaying the severity of the 2012 drought. Meteorologists pour over weather statistics providing graphs that show number of days over 100 degrees Fahrenheit or number of days without precipitation. Based on those number, they compare this year to past events. Then some weather experts give it a tagline of "worst drought in since 1956."
However, Bill Wiebold, MU soybean specialists said that crop productivity is a good indicator of drought intensity. Wiebold combed through data from over the decades to determine just how well crops performed during the early drought years versus how well they performed this year. He outlined his results in a recent Integrated Pest Management article from the University of Missouri.
What he concluded was that "drought severity, as calculated by corn yield loss, was greater in 2012 than for any year within the past 50 years."
"Crop productivity is also an excellent indicator of drought intensity," he said. "Most grain crops have specific stages of development when their yields are most sensitive to drought stress, so timing of stress also influences the amount of yield loss
According to Wiebold's findings, corn's most sensitive stage is a three-week period centered on R1 or commonly known as "silking." The stress placed on plants at this stage reduced the number of fertilized flowers. Stress after silking, he states, will result in increased kernel abortion, and if the stress has not been relieved, reduced seed size.
During mid-vegetative stages, corn may be so stressed that it reduces ear size, plant height and leaf size.
For soybeans, the most sensitive stage is during pod development. Stress at this time reduces the number of flowers and small pods that are retained on the plant. According to Wiebold, these R3 and R4 stages usually occur in late July and early to mid-August in Missouri. Stress during seed filling can result in additional pod abscission, arrested development of one or more seeds in retained pods, and reduced seed size.
During vegetative stages and early reproductive stages, stress may reduce plant height, branch elongation, and leaf size. Usually, drought stress during early vegetative stages has little effect on grain yield. In 2012, some Missouri soybean fields were planted while soils were too dry to promote germination and emergence. Unfortunately, in many of these fields, spring rains never occurred and emergence was spotty.
"Unfortunately in 2012," Wiebold explained, "corn plants, at least in some parts of Missouri, were affected by drought stress from shortly after emergence through the end of grain filling." In September, USDA estimated the state average corn yield would be 75 bushels per acre, which is 46% below a trend line yield that he calculated starting in 1963.
Using data from the National Agricultural Statistics Service, Wiebold found that during the drought of 2012 weather parameters were often compared to previous years such as 1980, 1983, and 1988. During those years, state corn yield averages were 39%, 45%, and 24% below trend line in those years, respectively, he noted.
Wiebold noted that many farmers he talked with said that the weather in 2012 reminded them of 1988. However, statewide, the yield loss in 1988 was only half of the estimated yield loss in 2012. The 1988 yield loss ranks 6th among yield losses for the past 50 years, Wiebold pointed out. The stressful weather and yield losses in 1988 were located mostly in the northern third of the state.
In August, USDA/NASS estimated the state average soybean yield would be 30 bushels per acre. "That estimate was reduced to 28 bushels per acre in September, which is 28% below trend line yield," Wiebold stated.
According to his research, the greatest yield loss from drought for soybeans came in 1983, 1984, and 2012. Soybean yield loss in 1980 was only 12%, which ranks 9th among all years.
Wiebold noted that corn and soybean respond somewhat differently to drought. "Part of the reason could be the timing of stress in any one year," he said. "Indeterminate soybean varieties possess a development cycle in which vegetative and reproductive growth overlap. And, within a soybean plant development stages among nodes can differ greatly."
Like those corn farmers, soybean farmers also stated that this year's weather reminded them of the weather back in 1988. Again, statewide yield loss for that year was only half of the yield loss in 1983 and 1984. The 1988 yield loss ranks 8th among yield losses for the past 50 years. The stressful weather and soybean yield losses in 1988 were located primarily in northwest and eastern Missouri.
For farmers, the drought of 2012 will undoubtedly go down as one to remember. Not only was it weeks without moisture, unrelenting temperatures, but as Wiebold points out a loss in production that surpasses any drought in the last 50 years.
Source: MU Integrated Pest Management