Farmers across the country would do well to condition their soils to weather rainfall and temperature extremes. That's what Jerry Hatfield says of a pattern of ever-wetter springs in the Midwest and in other areas drier, warmer summers -- a pattern he only expects to get worse.
The Midwest is seeing a shift to more intense spring rains, and more rain overall in the spring and summer, with some dry and hot summers mixed in, says Hatfield, Director of the USDA-ARS National Laboratory for Agriculture and the Environment in Ames, Iowa.
“Our trends in climate are towards the extremes,” he says. “Extreme wet, extreme dry, very cold, and very hot. This isn't a projection; it's what's happening.”
Increased precipitation in spring caused the number of workable field days to drop by three and a half days in the fifteen year period from 1995 to 2010, compared to the previous 15 years. "I project it will get worse in the next 20 years,” adds Hatfield.
In Iowa last year, State Climatologist Harry Hillaker says April and May were the wettest in 141 years -- then July, August, and September were very dry.
Soil water storage is key
More intense rainfall events in spring, followed by hot, dry summers, will have a negative impact on crops unless soil water storage capacity is increased, Hatfield says.
“I've spent 40 years measuring soil water capacity, and learned that the more we can build soil structure, the less water is needed for the crop," he explains. "A degraded soil has less water holding capacity, and that causes more runoff and erosion, further degrading the soil. It's a vicious cycle.”
Even a small rainfall event can cause slaking and sealing off the surface of the soil. As little as 1/32” inch of rain can seal soil pores, preventing water from infiltrating into the soil. But good soil structure can make a 2-inch rain seem like a 1-inch rain in terms of infiltration into the soil, he adds.
Weatherize with cover crops
Cover crops work in a number of ways to temper extremes in precipitation and temperature.
“Corn and soybeans can take all the water from the soil profile in warmer summers, and we’ll increasingly be depending on fall rains to replenish the soil profile,” Hatfield says. “People say cover crops use water. They do, but the timing of their use fits the patterns of increased rainfall. Cereal rye takes 3 inches of water in the fall and another 3 to 4 inches in the spring to grow very tall. But it also builds the soil’s capacity to store water in the profile for crop use later in the year.”
With cover crops in use, Hatfield has seen positive changes in soil structure, especially in the top half inch of soil, in as little as two years. “On the other side, I've seen crusting and broken-down soil structure within a year of discontinuing cover crops,” he says.
The bottom line is cover crops can provide climate resilience, Hatfield says.
“Cover crops protect the soil at the time of year we’re getting more intense rainfall. They help that water infiltrate rather than run off. They use some of that water to grow and sequester nitrogen, which can be helpful in wet springs, but they also help hold water longer and deeper in the soil profile since they build soil structure,” Hatfield says. “So, that water is there for crops later in the dry summer. I think cover crops are underrated in what they can do for the soil.”
– Betts writes from Iowa