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Title:   Author  item
                                            Dulaney, Wayneitem
                                            Daughtry, Craigitem
                                            Walthall, Charlesitem
                                            Timlin, Dennisitem
                                            Gish, Timothyitem
                                            KUNG, SAMUEL - UNIVERSITY OF WISCONSIN
  Submitted to: European Conference on Precision Agriculture Proceedings
                                    Publication Type: Proceedings
                                    Publication Acceptance Date: 11/1/2000
                                    Publication  Date: 7/16/2000
                                    Citation: N/AInterpretive Summary: The advent of new spatial information technologies and techniques, such as the global positioning system (GPS), geographical information systems (GIS), remote sensing, geostatistics, and variable rate applicators, have made it possible to manage agricultural production systems on a spatial or site-specific basis.  A marked increase in the efficiency of farm  operations would be achieved if inputs were applied so as to meet, but not exceed, localized crop requirements.  In theory, yield would be maximized while agricultural chemical losses to the environment, due to over application, would be minimized.  Successful implementation of site-specific production practices requires an understanding of those factors responsible for the spatial and temporal variability of crop growth and yield.  Moisture availability is often cited as the principal factor controlling yield response in rain-fed agricultural production  systems.  Data acquired during two consecutive drought years (1998 and 1999) provide an opportunity to assess the relative importance of soil chemical and physical properties on yield response under water-limiting conditions and to evaluate whether GPR image profile data can be used to identify field-scale, groundwater flow pathways that may act as subsurface irrigation.  This investigation concluded that knowledge of the spatial distribution of soil chemical and physical properties normally associated with crop growth and development contributed little to understanding spatial patterns of yield response when moisture availability is a critical factor; however, field-scale, subsurface flow pathways were predictive of high yielding areas during periods of severe drought.
                                Technical Abstract: Water availability is often the most limiting factor controlling crop growth and yield in rain-fed agricultural production systems.  A 20 ha research site was used to evaluate the use of ground-penetrating radar (GPR) and remotely sensed data to help understand the spatial and temporal variability of corn grain yield during two consecutive drought years.  Aerial color infrared imagery and yield monitor data revealed a high degree of spatial correlation.  Yield response was not well explained by the variability in soil chemical and physical properties.  Georeferenced, GPR image profile data were collected and analyzed using geostatistical techniques in order to determine the orientation and depth of subsurface restricting layers which govern the magnitude and direction of groundwater movement.  Hydrologic models were used to determine groundwater flow patterns from the subsurface topography.  A comparison of the spatial  distribution of corn grain yield and the subsurface flow pathways showed a high degree of spatial correlation suggesting that the movement of groundwater along restricting layers may act as a subsurface irrigation system increasing crop growth.  These results support the idea that under water-limiting conditions, knowledge of the subsurface stratigraphy may be critical to understanding and managing the spatial and temporal dynamics of crop growth and yield.


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