Greenhouse Gases & Gully-Washers

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It’s been a dry fall in Minnesota, and that means farmers have had plenty of opportunities to till up the soil after harvest. While driving around in farm country the day before Thanksgiving, I was struck by just how much corn and soybean stubble has been made subterranean the past few weeks. Acre-after-acre of rolling fields are black, giving crop producers a jump on spring planting. The trouble is, spring planting is several months off, and it’s inevitable a lot of that soil will be blown and washed away before it’s put back into use, especially if another open, relatively snow-less winter settles in. All of this exposed soil is particularly troubling considering how global climate change is making our agricultural lands even more vulnerable. So vulnerable, in fact, that attempts to put a positive spin on the greenhouse effect’s relationship to food production are losing steam fast.

Here’s the spin: There is evidence that as greenhouse gases build up in the atmosphere, yields of crops such as wheat, rice and soybeans will increase. Plants use greenhouse gases such as carbon dioxide as a type of “gaseous fertilizer.” Global climate change will also change where we grow certain crops. We’ll be raising corn around Hudson Bay if things keep going the way they are now. Agricultural powerhouses like the Red River Valley of the North are already seeing wheat and other small grains being pushed out by corn and soybeans, which are more tolerant of wet, humid conditions.

Now here’s the dirty reality: Global climate change poses a significant threat to our soil’s ability to produce food at all, no matter what the yield or where it’s being produced. For example, in recent decades the majority of North America’s precipitation has come in the form of intensive rainstorms. Since 1970, there has been a marked increase in heavy rainstorm events in the U.S., especially in the Midwest, Great Lakes regions and the Southwest, says the Bulletin of the American Meteorological Society.

A nice slow all-day drizzle provides ample opportunity for moisture to soak
deep into the earth. But heavy downpours that overwhelm the landscape in a matter
of hours, sending water running over the top of the ground instead of into it, are increasingly the norm. Modeling studies show “extreme precipitation
events” will continue to become more common in the future.

The result? An agro-ecological disaster in the making, say scientists Jerry Hatfield and John Prueger of the USDA’s National Soil Tilth Laboratory. These more intense rains are much more erosive, say the scientists, who examined the impacts of changing precipitation patterns on water quality in a paper published in the
January/February 2004 issue of the Journal of Soil and Water Conservation. A special report, “Conservation Implications of Climate Change: Soil Erosion and Runoff from
estimates that changes in precipitation patterns could be increasing soil erosion by as much as 95 percent in some areas.

That’s a disheartening statistic after all of the recent progress made in reducing erosion rates using no-till, high residue farming and other conservation tillage methods. Soil isn’t the only thing affected by changing weather patterns; the more water that runs off the surface of a field rather than soaking in, the more pollutants it will carry to rivers and lakes. Liquid manure runoff in particular could be a problem, since it is already saturated with water when applied to the land as fertilizer.

Hatfield and Prueger express concern that even “state-of-the-art” soil management won’t be good enough to deal with these increased erosion rates, and that significant
changes in farming practices will be needed to keep soils productive. These concerns aren’t all of the future tense variety. Farmers and soil scientists are already
seeing good soil management practices being overwhelmed by intense rainstorms.

For example, a study in Minnesota’s Scott County just south of the Twin Cities recently provided a glimpse at what could be a dire future. The study, which took place in the Sand Creek watershed, showed that chisel plowing, a sound conservation tillage method that leaves more soil-protecting plant residue on top of the ground, still resulted in about five tons per acre of erosion on a corn field during a particularly heavy June rainstorm. That five tons is about equivalent to a small dump truck. That’s well beyond the rate at which soil can sustainably replace itself through breakdown of vegetative matter, etc. The storm came at a time when corn plants had not yet developed sufficient foliage to protect the soil from rain drops. In fact, the window of protection for soil on a typical corn or soybean field is only a few months wide. A lot of damage can be wreaked by dirt-pounding storms (and steady winds) the rest of the year.

But the study also provided a glimpse at a more positive future, a future where farms find ways to protect the soil even under extreme conditions. During that same June storm, a Sand Creek dairy farm that was planted to alfalfa hay and rotationally grazed pastures lost 53 pounds of soil per acre—or just enough to fill a five-gallon bucket. A bucket versus a dump truck—that’s quite a difference. The credit for the reduced erosion on the dairy farm goes to perennial plant systems like grass and hay forage that protect the soil all year-round, instead of just a few months in the summer and fall. Just as important, this particular dairy farm has found that their soil-friendly methods are also profitable.

Sometimes words aren’t enough to get your mind around a dramatic situation. I went to Scott County and took a photo of a five-gallon bucket of soil sitting in front of a dump truck heaped with dirt. That photo and the accompanying article, “Same Storm-Different Outcomes” tell a “good news, bad news” type of story. The bad news? We could be sending a lot of soil south in coming decades. The good news? We have a choice, and there are farmers out there showing that we have the ability to execute that choice today.

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