By Lynn Betts
Farmers across the country would do well to condition their soils to weather rainfall and temperature extremes. That's what Dr. 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," Hatfield adds.
"Increased precipitation in the spring caused the number of workable field days in the spring to drop by three and a half days in the fifteen year period of 1995 to 2010, compared to the 15 years before that. We've been trending to wet springs in particular for the past 40 years, and I project it will get worse in the next 20 years," says Hatfield.
Look at last year's Iowa weather. State Climatologist Harry Hillaker says April and May were the wettest in 141 years -- then July, August, and September were very dry. "April and May precipitation was 5 inches in 1930, but nearly 10 inches in recent years," Hillaker says. "Last year was the 5th driest July and August. The overall trend is for more annual precipitation in Iowa; almost all that extra precipitation has come in the spring and summer of the year." Hillaker says March to May precipitation averaged 8.7 inches in the 1980's but jumped to an average of 11.6 inches over the past 10 years. That's a 33% increase -- he says there's also a 50% increase in the intensity of rains over the past 70 years.
Soil water storage is key
The impact more intense rainfall events in the spring followed by hot, dry summers will have on crops will depend on the water storage capacity of the soil, 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. A degraded soil has less water holding capacity, and that causes more runoff and erosion, further degrading the soil," he says. "It's a vicious cycle."