AMES, Iowa — According to the U.S. Drought monitor, the majority of Iowa has endured drought conditions since the beginning of the growing season, varying from extreme or exceptional drought to moderate drought. Despite this, the USDA reports that corn and soybean yields have remained relatively steady since last year.
As of October, corn yields are expected to average 199 bushels per acre, down 1 bushel per acre from the same time last year, while soybean yields are expected to average 58 bushels per acre, down 0.5 bushels per acre from the same time last year. How can yields remain steady given the drought that much of the state has endured?
As Iowa State University Extension and Outreach experts explain, classifying the drought status of an area takes a variety of factors into consideration, making drought classification just as complex as the impacts of drought.
Daryl Herzmann, a systems analyst with the Iowa State University Department of Agronomy, works extensively with the Iowa Environmental Mesonet, which is a key resource for researchers and agronomists across the state. The mesonet is a network of automated weather stations located across the state that provide meteorological data, including rainfall, temperature and wind conditions. The ISU Soil Moisture Network, which is part of the Iowa Environmental Mesonet, is particularly important in understanding drought across the state, as Herzmann explained.
“It’s difficult to observe trends in soil moisture over long periods of time, since moisture is a physically bounded quantity, and soil can only hold so much moisture,” clarified Herzmann. “That being said, the analysis this year was that there was just enough soil moisture to start out the growing season thanks to a rather wet winter, which ultimately saved crops across the state. Because of that deep soil moisture, a lot of places in the state that didn’t receive significant rain in July and August were able to pull through.”
“Additionally, there is some benefit to crops experiencing dry conditions early in the season, since drier surface conditions encourage crops to put their roots down deeper, which allows them to be more resilient later in the season,” added Herzmann.
“We really saw some miracles this year for yield,” he said. “Talking to farmers, yields were remarkable this year even without much rain.”
If soil moisture was sufficient to mitigate the impacts of lack of rainfall, then why has the state’s drought status remained severe? While soil moisture is considered when classifying an area’s drought status, drought status takes a variety of other factors into consideration, according to Herzmann.
“The U.S Drought monitor is a project put together by a team of authors, and every week, these authors collaborate with different communities to assess a wide variety of factors,” he said. “Soil moisture is a factor, but impacts are the most important factor considered by the drought monitor. For example, even if the soil moisture in some communities prevented yields from being impacted, those same communities could be under water usage restrictions, which would place them in a more severe drought classification. On the flip side, even if a community hasn’t gotten rain in weeks, there might be a lack of impacts, placing that community into a less severe drought category.”
Setting a Trend
The fact that trends in soil moisture are difficult to observe over long periods of time has been further exacerbated by increasing variability in precipitation and weather patterns, according to Catherine DeLong, water quality program manager with ISU Extension and Outreach.
“It’s really tough to see trends anymore,” explained DeLong, “in terms of soil moisture and precipitation being above or below average, we’ve seen a lot of ‘weather whiplash’ or a quick shift between two opposing weather conditions. We’ve also seen a lot of variability across the state, with some parts of the state being above average while others remain below average.”
While it may be difficult to see trends in soil moisture and precipitation across a given season, DeLong said that the general trend this year, with soil moisture held over from a wetter winter and spring providing key moisture for crops as precipitation tapers off, may become more and more common in Iowa.
“In general, we are predicted to experience wetter springs, wetter falls, and drier summers,” she added. “Given the more extreme conditions we’ve been experiencing, agricultural stakeholders and water resource professionals need to shift from planning for more average years to planning for more extreme years.”
According to DeLong, one important way for row crop farmers prepare for more extreme years is by building soil resiliency through the use of cover crops, which increase infiltration and water holding capacity to take full advantage of precipitation at any time of the year. For more information on cover crops, visit the Cover Crop page on the Integrated Crop Management website, or contact Catherine DeLong at 515-294-5963, or by email at firstname.lastname@example.org
For more information, visit the Iowa Environmental Mesonet.
— Iowa State University Extension and Outreach