Fig. 2. Zones based on bare soil color in 21.3-m grid format. Thin lines are original zone lines drawn on aerial image. Thick lines are the arbitrary boundaries between areas of varying N credit for soybeans in 2000. The N credits for 2001 fertilizer recommendation were 34, 22, and 45 kg N ha^–1 for the west, center, and east portions of the field, respectively. The extracted plots in the lower two maps are Treatments V1 and V2, which were both based on bare soil color in 2001.