• Paul Overby believes in trial and error. Since 1993 he and his wife, Diane, have been running Lee Farms, the family farm spread over 1,400 acres (5.5 km sq) in North Dakota, near the US-Canada border. In that time they’ve changed course quite a few times: diversifying the grains they grow, starting to manage the soil according to individualised zones, limiting the tillage of the land, and experimenting with planting cover crops alongside their main commodity crops.