Farmers adapting to heavier springtime rainfall patterns
It’s not just your imagination. It really is raining more in the springtime than it used to, according to Christopher Anderson, assistant director of the Climate Science Program at Iowa State University.
Since 1981, Iowa has received more than 11 inches of rain during May and June nearly 1 out of every 3 years, Anderson reports. That only happened 1 in 10 years, on average, during the previous 88 years, he notes.
"This is a level of risk previous generations of farmers didn’t have to deal with," he says. "It’s not just something that has happened in Iowa. It’s part of a broader shift in rainfall (across the Midwest)."
Records show that Iowa’s May-June rainfall has averaged 9.5 to 10.5 inches since the year 2000, compared to 7 to 8 inches in the 20 years before that, Anderson said.
Unusual spring and summer precipitation patterns have also occurred much more frequently since 1980, Anderson says. For example, he explains, exceedingly wet or dry springs are followed by excessively wet or dry summers with much greater regularity than before.
The increased rainfall has prompted farmers to target conservation practices to erosion-prone areas, expand conservation coverage on more acres and adapt agronomic practices to prevent excessive soil erosion and downstream sedimentation.
Cover crops and no-till slow the velocity of rainfall before it contacts the soil. Grassed waterways, buffer strips and terraces slow the movement of water from farm fields. Tile drainage increases the water holding capacity of the soil, reducing surface erosion. Fertilizer applications have also evolved, with more farmers utilizing nitrogen stabilizers and splitting applications into smaller doses applied later in the season so fertilizer remains present in the soil when crops need it.
Researchers are also examining strategies to reduce costs on lower-producing soils, such as conservation plantings or alternative crops.
"Either moving that highly-erodible land out of production, or at the very least, having a cover on it," Anderson says. "We definitely see the environmental value of putting in an extended rotation, but the business value, we have yet to see a rotation that works."
So why is Iowa receiving so much more rain during the spring months? Like many weather trends, it all starts with the ocean, Anderson explains. Warmer-than-normal Atlantic Ocean temperatures mean excessive spring rainfall in Iowa, he says. The trend, which generally occurs in roughly 60-year cycles, went from cold to warm in the mid-1990s.
"We’re close to the peak," Anderson says. "If we haven’t hit it yet, we’re going to in the next 10 to 15 years."
Warming air temperatures are also a trigger for increased rainfall, he adds. If temperatures rise by one degree Celsius from 2020 to 2045, as predicted, Iowa can expect an additional inch of rain during May and June, Anderson says. That means fewer days suitable for field work, among other consequences.
"We have about 5 to 20 years to get ready," he says.
Along with conservation practices, farmers could also cope by utilizing water management practices, Anderson says. For example, while irrigation is sparsely used in Iowa, there are opportunities to capture some of the abundant spring rainfall and hold it in a storage basin for irrigation usage later in the year if the weather turns dry, Anderson says. Studies suggest managing water to have dry soils at planting time and wet soils during the summer months could increase corn and soybean yields by as much as 13 percent compared to trendline yields, Anderson says.
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