American farms like this iceberg lettuce field owned by Duda Farm Fresh Foods outside Salinas, Calif., are facing a dwindling supply of farmworkers from rural Mexico. Kirk Siegler hide caption

itoggle caption Kirk Siegler

Cows wait to be milked at a California dairy farm. Justin Sullivan/Getty Images hide caption

itoggle caption Justin Sullivan/Getty Images

Thick jets of processed sewage arc out 30 to 40 feet from giant moving spreaders at Birmingham Farm in Kansas City, Mo. Frank Morris for NPR hide caption

itoggle caption Frank Morris for NPR

Farmers harvest a sugar beet crop in Gilcrest, Colo. Matthew Staver/Landov hide caption

itoggle caption Matthew Staver/Landov

Wild bees, such as this Andrena bee visiting highbush blueberry flowers, play a key role in boosting crop yields. Left photo by Rufus Isaac/AAAS; Right photo courtesy of Daniel M.N. Turner hide caption

itoggle caption Left photo by Rufus Isaac/AAAS; Right photo courtesy of Daniel M.N. Turner

Peanut plants grow on a Halifax, N.C., farm that received federal subsidies in 2011. Robert Willett/MCT /Landov hide caption

itoggle caption Robert Willett/MCT /Landov

A soybean field near Campo Verde in western Brazil in January 2011. Researchers argue that enough arable land is already under cultivation to feed the planet for the next several decades. Yasuyoshi Chiba/AFP/GettyImages hide caption

itoggle caption Yasuyoshi Chiba/AFP/GettyImages

Chris Costa and one of her chickens on her farm in Downingtown, Pa. Costa and her partner, T.J., found the land for this farm through a sustainable agriculture program. Emma Lee/WHYY hide caption

itoggle caption Emma Lee/WHYY

Orchards like this one in Adams County, PA, and other U.S. farms face worldwide competition for their apples and apple products due to imports. Brad C. Bower/AP hide caption

itoggle caption Brad C. Bower/AP