Fig. 1. Delineation of major climatic zones in the USA based on mean annual temperature (cool, <12°C; warm, 12°C) and mean annual precipitation (dry, <750 mm; humid, 750 mm). Produced by H.J. Causarano using the Spatial Climate Analysis Service (www.ocs.orst.edu/prism/).
Fig. 2. Mean monthly climatic conditions at four different locations within the southeastern USA. MAT is mean annual temperature and MAP is mean annual precipitation. Potential evapotranspiration was calculated using the Thornthwaite equation (Thornthwaite et al., 1957). Data from 1961 to 1990 (National Climatic Data Center, www.ncdc.noaa.gov/oa/ncdc.html).
Fig. 3. Corn grain yield response to N fertilizer as affected by previous cropping. Perennial grass phase was 3 yr. Data from 1958 to 1964 near Watkinsville, GA (Adams et al., 1970a).
Fig. 4. Nitrogen uptake by sorghum–sudangrass grown in the greenhouse (a) and corn grain yield in the field (b) as affected by number of years previously in tall fescue (in fescue) and number of years since tall fescue terminated (out of fescue). Data collected near Watkinsville, GA (Giddens et al., 1971a, 1971b).
Fig. 5. Relationship of peanut yield to incidence of stem rot (Sclerotinium rolfsii) as influenced by crop rotation system in Georgia. Mean yield of the four treatments within each year was set as 100% yield. Data from 1993 to 1999 near Tifton, GA (Brenneman et al., 2003).
Fig. 7. Corn grain yield response to N fertilizer as affected by cover crop management. Georgia data from 1958 to 1964 near Watkinsville (Adams et al., 1970a). North Carolina data from 1984 (McLeansville) and 1985 (Reidsville) (Wagger, 1989).
Fig. 8. Relationship of soil bulk density with soil organic C concentration from a pasture experiment near Watkinsville, GA. Data from 0- to 2-cm depth (Franzluebbers et al., 2001).
Fig. 9. Corn grain yield and tall fescue forage yield components in response to corn planting density when strip-killed into living tall fescue sod from 1972 to 1973 with supplemental irrigation to maintain high soil water availability near Watkinsville, GA (Harper et al., 1980). Shaded areas correspond to the zone of maximum corn grain yield production (centered at 75 000 plants ha–1).
Fig. 10. Soil organic C concentration with depth as affected by tillage management and year of sampling (Franzluebbers and Stuedemann, 2005). *** Denotes significance between tillage means within a depth at p 0.001.
12°C) and mean annual precipitation (dry, <750 mm; humid, 
0.001.