Consider the two soil samples pictured here. The darker soil (below left) comes from a restored prairie site at Fermilab, where dedicated crews have been reclaiming former farmland for more than 25 years. The lighter soil comes from the farm. When drops of water fall on this soil, instead clumping, it crumbles and washes away. This soil lacks the numerous mycorrhizal fungi and subsurface structures that retain water, hold it together, and make it rich.

A longterm study by the Research Institute of Organic Agriculture in Switzerland and published in late May in Science compared organic farming methods with conventional ones. Researchers found that organic farmers added 34 to 51 percent less nitrogen, phosphorus and other nutrients to the soil than conventional farmer, yet their crops yielded only 20 percent less, demonstrating that organic farms used resources more efficiently.

Organic soils also hosted a larger and more diverse group of soil-building microbes. Beneficial insects were nearly twice as abundant and more diverse, including pest-eating spiders and beetles. The researchers concluded that organic farming's compatibility with biodiversity fosters sustainably fertile soils.