Site-specific analysis of a droughted corn crop: I. Growth and grain yield

Soil in the southeastern USA Coastal Plain exhibits marked variation, espec ially near shallow depressions called Carolina Bays. This variation causes correspondingly severe variation in yield, particularly for corn (Zea mays L.) during drought. Though important to precision farming, these features o ften are overlooked in 1:20 000 scale county soil surveys, They are visible in 1:1200 stale soil surveys, but the ability to explain yield variation u sing soil map units at this scale must be unequivocally demonstrated before committing resources to such a detailed survey. Our objectives were (i) to compare paired samples of four soil map units to determine if grain yield variation were sufficiently explained to be of practical value, and (ii) to extend this evaluation to include data with greater spatial coverage. Corn grain yields were measured at 209 sites in an 8-ha field, including two Ca rolina Bays near Florence, SC. Site-specific effects of soil variation on c rop phenology, biomass, and yield components were measured at 11 sites duri ng a drought. Variations in yield components were large and sometimes compe nsatory (e.g., kernel number and mass), with distinctly different routes to sometimes similar final grain yields. Multiple sites within map units were frequently different at alpha = 0.05. Analysis of variance for grain yield on soil map unit was statistically significant (P < 0.001) but of limited explanatory value (r(2) = 0.16). We conclude that to create soil management zones for precision farming, one must augment even detailed soil map units with additional spatial data, such as yield maps.