Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 26, 1999
Publication Date: N/A
Interpretive Summary: Aerial views of the Coastal Plains show noticeable soil patterns. Usually, yield maps from the region have similar patterns in crop yield as well. Explaining the causes of yield variation by studying the soils and the crop response to both the soils and the weather is one objective of researchers in site-specific agriculture. Measurements made during a severe drought presented an opportunity to study crop response at many different levels of water stress, from apparently well watered all the way to nearly dead. Measurements of water stress, made with infrared thermometers, showed patterns related to detailed soil maps. Measurements of soil water content, and by difference, soil water use, showed patterns as well. Timing of the stress and water use was shown to impact the growth and yield of the corn crop, affecting yield components including kernel number and size. We concluded that final yield can be achieved in many different ways, which complicates interpretation of yield maps now becoming available. Accounting for the many interactions appears to require computer models, for which this season's data is ideally suited.
Technical Abstract: The southeastern Coastal Plain has spatially variable soils and crop yield. Corn (Zea mays) appears to be particularly variable during drought. A severe regional drought provided a unique opportunity to both observe yield variation and examine its specific causes. Corn yields were measured at 209 sites in an 8-ha field. At eight sites, site-specific crop water use was calculated from soil moisture measured using time-domain reflectometry (TDR). On eight transects, drought stress was evaluated during vegetative growth using infrared thermometer (IRT) measurements of canopy temperature (Tc). During the most severe drought, visibly stressed areas had canopy-air temperature differences (Tc-Ta) above 10 deg C, yet other areas remained below 2 deg C. A 46-mm rain reduced Tc-Ta to near zero for all sites, indicating that most water stress was relieved. The water balance results were dominated by site-to-site differences in runoff and evapotranspiration. Water stress inferred from water use matched stress inferred from yield components. In sum, corn at the eight sites arrived at similar final yields via fundamentally different paths. These results underscore the need for within-season observations of crop growth and of stress to facilitate interpretation of site-specific yield maps.