If you ask Jerry Hatfield, the 2012 drought wasn’t just a blip on the radar screen.
While crop production mostly recovered from the drought of 1988 during the following growing season, the USDA-ARS researcher sees a long-term dry period emerging in the U.S. that is similar to the 1930s.
Wet springs with active weather patterns, followed by hot, moisture-limited summers, could be more the rule than the exception in the coming decades. But no-till systems, managed properly, could help farmers weatherproof their farm against heavy rain and scorching droughts, rather than continually becoming victims of Mother Nature.
“The drought of 2012 taught us one very important lesson: good soils and good soil management paid in spades,” he says.
Rainfall More Intense
Farms across the Midwest are already seeing a change in spring precipitation patterns, with more falling in spring than summer. In Ames, Iowa, for example, an uptick in precipitation in April and May began during the 1990s.
Research by the ARS found in Iowa a reduction in workable field days between April 1 and mid-May of 3½ days over the last 20 years due to higher numbers of significant rainfall events. Using Des Moines as another example, more and more days have been seen every year with high-rainfall events of more than 1½ or 1¼ inches.
“If you look in the early part of the 20th century, we only had 2 years that had more than 8 days with 1¼ inches of rain,” he says. “Since 1975, we’ve had 8 years with that, so we’ve seen more and more intense rainfall events.
“We see a shift in more springtime events. We’re picking up more rainfall early in the year, and it’s coming in a much more intense matter.”
For the whole U.S., looking at summer precipitation in June, July and August, climate models all seem to agree that a much drier environment will persist, he adds.
“We’ve built our whole cropping system across the Midwest on summer precipitation. When we project more shifts away from summer rains, it means we’re more and more likely to have water stress.”
Evidence suggests that temperatures across the U.S. are changing as well, although the heating isn’t the same in every region.
Data from the University of Delaware describing temperature changes in the 20th century (1901 to 2008) showed that surface air temperatures in the upper Midwest — roughly north of Interstate 80 — have warmed slightly, and the Southeast has cooled, Hatfield says.
Two different models Hatfield has shared show a general warming trend enveloping the U.S. through the 2040s, with more severe warming expected during the 2080s. One model depicts warming trends will be more extreme in the western Corn Belt and Great Plains during those periods than in states farther east.
Warming temperatures in major crop-producing states will likely increase crop-water demand, Hatfield says. The warmer the temperature, the more water the atmosphere can hold and the higher the evaporative rate is seen from plants.
“If I’m under a limited water supply in a high-temperature condition, I can have plants under stress very, very quickly,” he adds. “And crops will go under stress more quickly in soils that have a limited water-holding capacity.
“If you’ve got a sandy spot in a field, what spot goes under water stress first? The sandy spot. It has less water available.”
A Variable Picture
Hatfield says farmers in corn-producing states like Iowa, Illinois and Indiana were able to produce a decent corn crop in 2012, in spite of the historic drought, because of moisture that built up in the soil profile during previous years.
Typically, Corn Belt states are so wet early in the year that roots don’t go too deep. And by the time tasseling occurs, he says, when water is being taken up to make grain available soil water will be limited by the rooting depth because roots are no longer growing.
But last spring, the cycle changed. Corn plants were able to root down very quickly, explore the soil profile and extract water before the drought began.
When researchers pulled soil samples last fall in Iowa, they found dry conditions down as far as 6 feet because subsoil moisture had been used up to produce the 2012 crop, Hatfield says.
Going forward, it will be critical for farmers to understand what’s happening with crop-water use if hot, dry summer conditions continue, Hatfield says.
Water leaves fields both by evaporation from the soil surface and from plant leaves through transpiration, where water travels through the roots and stem and out the leaves.
Both transpiration and evaporation make up “evapotranspiration,” but crop productivity is a direct function of transpiration by the crop.
Soil variability can factor heavily into a crop’s water-use efficiency and produce large fluctuations in yields across a field.
A soil type, such as Webster, may have 5% or 6% organic matter, and Clarion soils may have 1% to 2%.
Plants in some soils — such as Webster, in this case — may transpire twice as much water as other types of soils, such as Clarion, because there is more water available in these higher organic matter soils.
“Over the past few years, we’ve spent a lot of time looking at yield variation, crop-growth variation and water-use variation across fields, and yields will go all the way from 120 bushels to well over 250 across other parts of some fields,” Hatfield says.
In soybeans, Hatfield noted one field in central Iowa from early August 2012 that had little or no variation in canopy; but 3 weeks later, with no rain, “we went from a full canopy to losing a lot of leaf area,” Hatfield says. “The yield variation in this field went from 25 bushels to about 65 bushels.
“That’s about a 40-bushel difference in yield just because it didn’t rain for 3 weeks. So a plant’s ability to extract water is dependent upon how much water is stored within the soil profile. That becomes the piece that you can manage.”
Water Efficiency Key
If long-term weather models are correct, water-use efficiency is a term that won’t just pertain to irrigated acres west of the Missouri River anymore, Hatfield says. It will need to become part of the vernacular with farmers in rain-fed states in the core Midwestern Corn Belt.
Rainy springs and hot, dry summers could also have implications for crop selection. Farmers in some states may find that small grains are more attractive because those crops grow earlier and mature before hot summers arrive, Hatfield suggests. Or early-planted, short-season corn varieties could be favored more.
“Up until now, we really haven’t talked much about how much grain we get per unit of water that’s transpired,” he says. “We do that in irrigated areas all the time because water is an expensive commodity. But in rain-fed areas, we’ve kind of blown it off.
“I think we’ve got to refocus on that because it’s a way in which we can look at our crop performance.”
If a majority of farmers are to hit the stated ag-industry goal of 300 bushels per acre in corn, they will have to transpire another 5 inches of water through the crop, Hatfield says.
“We’re going to have to have that 5 inches of water within that soil profile available to that crop during the grain-filling period,” he says. “Don’t count on rainfall being there to do that because it may not be raining at the time at which we need it.
“Three hundred bushels doesn’t come free.”
Don’t Till Fields
With conventional tillage still being the predominant practice, farm ground in the U.S. is becoming more fragile by the year — to a point, Hatfield says, where rainfall events of only 1 inch are triggering runoff events, rather than with 2½ or 3 inches of rain.
Tillage not only makes fields more vulnerable to erosion, but also speeds up evaporation of water from the soil surface. This was proven time and again as researchers in Ames monitored instruments measuring water evaporation in fields.
“Any time you go out and till in the spring, that’s half an inch of water going in the atmosphere,” Hatfield says. “Tillage does exactly what it’s supposed to do in the spring — it dries the soil out.
“Every time the producers tilled, we saw this major flush of water coming up. It hadn’t rained or anything else, and basically they were evaporating the water back out.
“Tillage is degrading our soil resource, and degrading both our water-holding capacity and water-infiltration rates. We’re just kind of accepting it in terms of agriculture.”
Research by retired USDA-ARS soil scientist Don Reicosky that looked at low- vs. high-disturbance drills found that high-disturbance drills caused moisture evaporation of 0.7 millimeters an hour, compared to 0.35 millimeters with low-disturbance drills and 0.17 millimeters with no disturbance.
“Over a 24-hour period, that’s a pretty substantial amount of water,” Hatfield says. “So the more intense we till that crop, the drier it becomes. We saw that this year as well.
“Those that did a lot of tillage and then planted had very uneven stands because they didn’t have the moisture to be able to germinate the crop.”
On Hatfield’s research fields, in a comparison of tillage studies over the past several years, no-till fields have consistently out-yielded other fields, he says. This occurred in 2010, when conditions were extremely wet, 2012 when it was extremely dry and in 2011 when the end of the year was dry.
“In 2010 when it was wet, no-till out-yielded everything else because the improved aggregate structure allowed the oxygen to move back and forth in that whole profile,” Hatfield says. “In 2011 and 2012, it was because of water availability and more water for transpiration.
“Your biggest key going into the future is water. Water trumps everything else in our farming systems, and no-till is a way in which we can manage that water very, very effectively.”
Keep The Residue
Hatfield believes the benefits of no-till come not just from not disturbing the soil, but from a continuous blanket of crop residue that protects the soil surface from rainfall impact and the extremes of weather.
Where uncovered fields allow moisture to escape into the atmosphere unfettered, residue cover reduces the soil water evaporation rate by roughly 60% to 70%, he says.
Another area where crop residue is beneficial is to increase the effectiveness of small precipitation events. Just as crop residue can buffer fields from intense rainstorms, plant matter also keeps more moisture in the soil profile.
“As raindrops make it through the residue, they wet that upper surface. If you’ve got clean-tilled soil out there, the water evaporates right back out,” Hatfield says.
Another piece of the puzzle is that residue layers buffer the soil from temperature extremes. This is important in terms of both root life and soil biological activity, Hatfield says.
“If you dig around in no-till systems, you’ll find the roots of those crops are very near the surface, where they can take advantage of the small precipitation events because that water doesn’t have to move down 6 to 8 inches for it to finally hit a root,” he says. “The roots are sometimes within 1 or 2 inches of the surface.”
When there’s no residue cover on fields, soil microbes may go from an extreme in early spring of possibly 40 F in the morning to 104 F in the afternoon during hot, dry periods. At soil temperatures of 104 F, proteins begin to denature and microbes become inactive, going into a quiescent state, Hatfield says.
“In these extremes, soil microbes can’t do their job,” he says. “If you really have an active biological system within the soil, it will consume all the residue and material that’s out there.
“We’re going to have to think differently about soil management and how we manage residue and soil biology as part of the overall puzzle to build the soil up over time, because it will become our weatherproofing mechanism.”
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