Stripping Erosion Control to its Bare Essentials

Posted by .

While walking through a knee-high prairie planted on a central Iowa hillside Tuesday, I happened to look down. Trapped amongst all that vegetation was an impressive amount of rich, black glacial soil, the kind that produces record crop yields. And just a few feet away was the source of that soil: a soybean field planted in a no-till system. I was getting a firsthand look at how planting just 10 percent of a crop field to native prairie can reduce soil erosion by 95 percent. As you can hear on LSP’s most recent podcast, this is a prime example of how a little nature can go along way in solving soil erosion and water quality problems.Back in 2003, a group of scientists and others in Iowa began discussing ways of using perennial plant systems like prairie to add some diversity to fields dominated by annual row crops like corn and soybeans. These people knew better than to propose replacing whole fields with perennial prairies—an idea that would be even less popular today what with corn selling for $7 per bushel. Instead, the idea was developed for planting 30-to-50 feet wide strips of prairie in strategic locations throughout crop fields.

Out of this idea has come STRIPs, which stands for Science-based Trials of Rowcrops Integrated with Prairies. Coordinated by Iowa State University’s Leopold Center for Sustainable Agriculture, this research project has been taking place since 2007 at the Neal Smith National Wildlife Refuge in central Iowa. This is an excellent place for such a study. For one thing, the topography provides a real challenge to keeping soil in place: slopes of 6 percent to 8 percent are not uncommon. In addition, the wildlife refuge is undergoing a long-term transition from crop fields to native prairie.

Scientists involved with the project told me during a tour this week that when the research started out the assumption was that planting native prairie in crop fields would provide some environmental benefits such as increased habitat for wildlife and pollinators. They also assumed the strips would slow overland water flow, allowing it to better soak in and reducing the amount of soil that would make its way to the bottom of these hills, and eventually into the wider watershed.

And yes, there has been an increase in the number of grassland bird species nesting in the studied crop fields, and yes, pollinators are doing well in the strips. But, as Matt Helmers and Matt Liebman told me in LSP’s podcast, researchers weren’t quite prepared with just how successful the strips would be at slowing down water and cutting erosion.

“I was and am surprised that it’s that dramatic,” said Helmers of the 95 percent reduction with just 10 percent of the field in strips. Helmers, an ISU agricultural engineer, says farmers are quite familiar with utilizing grass buffers to reduce erosion. But usually these are planted to cool season grasses like brome. Brome creates a nice, soil-friendly sod, but in really heavy rains tends to lay down, allowing water to race over it. Prairie plants, on the other hand, have erect, stiff stems that are better at impeding the movement of water, and anything it’s carrying along for the ride.

As I walked up the sloping soybean field inspecting the strips (they’re planted on the contour), ISU agronomist Matt Liebman explained that in 2008 heavy rains in late May and early June resulted in the part of the study field that’s not planted to prairie strips to lose on average 11 tons of soil per acre. The amount of soil lost in the stripped part of the field was measured in the hundreds of pounds that year. Indeed, on Tuesday when we inspected one of the flumes used to channel water and measure erosion in the 100 percent cropped field, soil was piled next to the device—it turns out researchers have had to clean out the flume to keep it from being clogged by eroding soil. Just a few yards away a flume that sat at the bottom of a prairie stripped section of the field was relatively clean.

“Sediment has never been cleared from this flume,” said Liebman.

Keep in mind that the part of the field that lacked strips was losing soil by the ton despite being farmed in a way considered highly sustainable. The narrow bean rows were growing amongst last year’s corn stalks and dead plant residue covered much of the soil, an indicator that a good no-till system was in place.

“Even though we are five years into no-till, we are not getting an elimination of soil loss just with no-till,” said Liebman.

Why? Part of the reason is that that during the past few years this region has been witness to an unprecedented spate of torrential rainfalls and floods. These storm events have caused significant erosion and runoff even on fields utilizing no-till production systems. “We have so much water coming down here that the residue just floats off, and at that point the soil is completely vulnerable,” said Liebman.

As the climate changes, even the best conservation tillage may not be good enough. “These kinds of high intensity events are occurring with a greater frequency,” Liebman told me. “Regardless of how people think that they’re coming about—whether they think they’re caused by people or just a change in climate that evolves independent of us—there are the thing that people have to deal with. And in the world of farmers, they’re looking at large amounts of nutrient loss, large amounts of sediment loss, increased threats to crop production. These kinds of things are catching people’s attention.”

In fact, the four years of results produced by the STRIPs research is catching the attention of not only environmental groups and natural resource professionals. On Tuesday, large crop farmers and representatives of commodity groups were on hand at the refuge to learn more about prairie strips. It seems one can look at record high crop prices, and the inflated land values that accompany them in two ways: 1) either market forces will justify planting every inch of land to row crops utilizing any method possible, or 2) that land will become too valuable to abuse.

One way or the other, now that prairie strips have proven they work, it’s time to get more of them established on working land. The crop farmers present Tuesday talked about how producers will adopt such systems, especially if they can see themselves how they benefit not only their own farms, but the community at large. They also talked about the importance of having personal contact with other farmers and agricultural experts who may live in their same watershed and who are willing to try something new.

The Chippewa 10% Project, which is being coordinated by LSP and the Chippewa River Watershed Project, is trying to utilize the latest science to integrate more perennials into one western Minnesota watershed. But it’s also relying on that most critical of resources: farmer-to-farmer knowledge transmission.

“One of the most powerful tools is the relationships people build with each other,” said Chippewa 10% coordinator Julia Ahlers Ness, who was also on the STRIPs tour Tuesday.

And as Liebman pointed out, those relationships go beyond the farm gate. Making something like prairie stripping viable for farmers means bringing together market forces, community needs and innovative policy. Said the agronomist, “We have to come to some broader agreements that protecting the productivity of our farmland is really important to all us, not just those who are farming it directly.”

Leave a Reply

  • (will not be published)