The activity of tiny microbes in and around the roots of crops such as soybeans are valuable for their growth. Oleh Malshakov/iStock/Getty Images Plus Across North America, in places such as Illinois, Iowa and Texas, farmers are busy growing the crops the world depends on for food, fuel and fiber. But as their tractors roll across fields, a pressing concern weighs heavily on many farmers: the rising cost of synthetic fertilizers, widely considered essential for crop production. After an expensiv