Submitted to: Precision Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/18/2005
Publication Date: 8/26/2005
Citation: Sadler, E.J., Evans, D.E., Gerwig, B.K., Millen, J.A., Thomas, W., Fussell, P. 2005. Severity, extent, and persistence of spatial yield variation in production fields in the SE US Coastal Plain. Precision Agriculture 6:379-398. Interpretive Summary: For many reasons, adoption of site-specific farming has been somewhat slower in the Southeast Coastal Plain than in other parts of the country. It appeared that many SE farm operators were waiting to see specific economic or environmental benefits before adopting the new technologies. However, such specific knowledge requires research that both is expensive and takes time. In the interim, preliminary calculations could be made of the potential economic and environmental impact of spatial yield variation if three questions could be answered: 1) how severe is the variation within a SE field?, 2) how widespread is the variation from field to field?, and 3) how persistent is the variation from year to year? These questions can be answered based on knowledge of variation before implementation of site-specific or variable-rate technology. Therefore, more than 12,000 acres of yield maps were collected from producer's combines in SE North Carolina. The analyses of these maps indicate that within-field variation in yield is sufficiently severe to indicate both potential economic benefit to site-specific techniques and environmental risk to whole-field culture. The variation appeared throughout the 5-county geographic extent of the dataset. Further, in many fields, yield patterns were sufficiently stable to suggest map-based variable-rate management could be done. The dataset can be used to explore the economic and environmental implications of yield variation in the SE Coastal Plain.
Technical Abstract: In the SE Coastal Plain, adoption of site-specific farming has lagged behind that in the upper Midwest. While changes may be both social and economic, site-specific severity, spatial extent, and affect on yield need to be quantified before adoption would be considered by many farm operators. Our objective was to document the severity, extent, and persistence of yield variation for corn, wheat, and soybean during normal production in this region. Farmer combines were outfitted with commercial yield monitors to produce yield maps. Corn, wheat, and soybean yields were mapped for three years on more than 4900 ha (12,000 acres). For each cooperator, crop, and year, summary statistics and cumulative yield distribution functions were also developed. Yield maps showed that substantial areas had yields either well below or well above the mean for the cooperator-crop-year. For instance, 25% of cooperator A's area had corn yields more than 30% below the mean yield of 5.06 Mg/ha, and another 25% had yields more than 31% above that mean, which indicate the severity of yield variation. Variation from county to county had no consistent difference indicating that the extent of the variation is widespread. Variation was also persistent from year to year, with more than 50% of the area in 15 of 17 fields having stable yields relative to the field mean. These data show the potential importance of variable-rate management in the region, and also hint at the potential environmental implications.