Editorial: Applications of apparent soil electrical conductivity in precision agriculture

Sustainable agriculture is considered the most viable means of meeting future food needs for the world's increasing population through its goal of delicately balancing crop productivity, profitability, natural resource utilization, sustainability of the soil-plant-water environment and environmental impacts. Precision agriculture is a proposed approach for achieving sustainable agriculture. Site-specific crop management (or site-specific management, SSM) refers to the application of precision agriculture to crop production. Site-specific crop management utilizes rapidly evolving information and electronic technologies to modify the management of soils, pests and crops in a site-specific manner as conditions within a field change spatially and temporarily. Geospatial measurements of apparent soil electrical conductivity (EC"a) are the most reliable and frequently used measurements to characterize within-field variability of edaphic properties for application to SSM. The collection of papers that comprises this special issue of Computers and Electronics in Agriculture provides a review of the current technology and understanding of geospatial measurements of EC"a and current approaches for their application in SSM. The objective of this preface is to run a thread through the papers to show their interrelationship and to identify significant points. The spectrum of topics covered by the papers include: (i) a review of the use of EC"a measurements in agriculture, (ii) multi-dimensional EC"a modeling and inversion, (iii) theory and principles elucidating the edaphic properties that influence the EC"a measurement, (iv) EC"a survey protocols for characterizing spatial variability, (v) EC"a-directed response surface sampling design, (vi) designing and evaluating field-scale experiments using geospatial EC"a measurements, (vii) mapping of soil properties with EC"a, (viii) spatially characterizing EC"a and water content with time domain reflectometry (TDR), (ix) delineating productivity and SSM zones and (x) SSM methods for reclaiming salt-affected soils. The greatest potential for the application of geospatial measurements of EC"a in SSM is to provide reliable spatial information for directing soil sampling to identify and characterize the spatial variability of edaphic properties influencing crop yield. This in turn can be used to delineate SSM units, which are key components of SSM. The future of SSM depends upon the continued development and integration of information and electronic technologies that can identify and characterize, both temporally and spatially, not only edaphic properties but also topographical, biological, meteorological and anthropogenic factors influencing within-field variations in crop productivity. The implementation of global positioning system (GPS)-controlled variable-rate equipment will need spatial information to effectively determine input application rates. Because of their reliability, ease of measurement and flexibility, geospatial EC"a data will undoubtedly contribute a significant portion of the spatial soils-related information needed to direct variable-rate equipment.