Back in Iowa, many farmers are attempting to protect and rebuild their precious black gold. Researchers at Iowa State University have been working with farmers to plant “prairie strips” on part of their fields. In return for a subsidy, farmers dedicate 10% of each crop field to native perennial grasses and plants that providing a valuable habitat for wildlife and pollinators. The strips also seem to help restore the soil.

Research has shown that the prairie strips can generate a 20-fold reduction in the amount of sediment being washed off fields. They also retain more nitrogen and phosphorous by helping to reduce the amount of water from running off the surface.

“The basic idea behind prairie strips is using the Midwest’s native ecosystem to improve our currently dominant corn-soybean agroecosystems,” says Lisa Schulte-Moore, co-leader of the project trialling their use.

Around 600 acres (242 hectares) of prairie strips have been created on around 65 farms in Iowa and some surrounding states. To create a prairie strip, farmers plant a mixture of plant species on part of their fields and leave it for two or three years to take root.

After this they have to actively maintain the integrity of the prairie by burning, mowing or grazing to help prevent annual weeds and invasive woody plants from taking over.

The researchers are now monitoring how the strips of prairie may alter soil health in the longer term.

“If a farmer terminates a prairie strip after it has been in place for five to 10 years, we know the soil health has been improved. But we want to know whether the crop will benefit from this and how long will that last,” says Rick Cruse, an expert in soil management at Iowa State University who is also involved in the project.

“What we envisage is that the farmer would move the strip to another part of the field and that would then be enriched. It could be a gamechanger for some farmers.”

On Paula Ellis’s farm in Iowa’s Lee County, she and her husband have been continuing a no-till farming approach that her father started almost 40 years ago. They also use cover crops like rye to keep plants growing on the soil at all times and have buffer strips similar to the prairie strips close to the creeks in their fields to help reduce run-off.

“You can really see a difference in the healthiness of the soil,” says Ellis. “It has a better structure. On the farms nearby that work up their ground all the time, you just don’t see that nice rich soil and it turns really hard and rocky.

“There is still a lot of work to be done. We have to do everything we can to keep our soil.”

Image credits: Jim Richardson, Katja Schulz, Matthew Wallenstein, Indigo Agriculture, The Land Institute, Getty Images

Graphics sources: Food and Agriculture Organization of the United Nations, United Nations Convention to Combat Desertification

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This article is part of a new multimedia series Follow the Food by BBC Future and BBC World News. Follow the Food investigates how agriculture is responding to the profound challenges of climate change, environmental degradation and a rapidly growing global population.

Our food supply chains are increasingly globalised, with crops grown on one continent to be consumed on another. The challenges to farming also span the world.

Follow the Food traces emerging answers to these problems – both high-tech and low-tech, local and global – from farmers, growers and researchers across six continents.