Characterizing soil spatial variability with apparent soil electrical conductivity I. Survey protocols

Spatial characterization of the variability of soil physico-chemical properties is a fundamental element of (i) soil quality assessment, (ii) modeling non-point source pollutants in soil, and (iii) sitespecific crop management. Apparent soil electrical conductivity (ECa) is a quick, reliable measurement that is frequently used for the spatio-temporal characterization of edaphic (e.g., salinity, water content, texture, and bulk density) and anthropogenic (e.g., leaching fraction) properties. It is the objective of this paper to provide the protocols for conducting a field-scale ECa survey (Part I) and apply these protocols to a soil quality assessment in central California’s San Joaquin Valley (Part II). The protocols are comprised of eight general steps: (i) site description and ECa survey design; (ii) ECa data collection with mobile GPS-based equipment; (iii) soil sampling design; (iv) soil core sampling; (v) laboratory analysis; (vi) calibration of ECa to ECe; (vii) spatial statistical analysis; (viii) GIS database development and graphic display. For each outlined step, detailed discussion and guidelines Abbreviations: CEC, cation exchange capacity; DPPC, dual pathway parallel conductance model; EC25 ◦C, electrical conductivity at 25 ◦ C; ECa, apparent soil electrical conductivity; ECe, electrical conductivity of the saturation extract; ECw, electrical conductivity of the soil solution; EM, electromagnetic induction; EMh, electromagnetic induction measurement in the horizontal coil-mode configuration; EMv, electromagnetic induction measurement in the vertical coil-mode configuration; ER, electrical resistivity; ESAP, ECe sampling, assessment and prediction software; ESP, exchangeable sodium percentage; GIS, geographic information system; GPS, global positioning system; IDW, inverse distance weighting; Ks, saturated hydraulic conductivity; LF, leaching fraction; NPS, non-point source; OM, organic matter; PW, percent water on a gravimetric basis; SAR, sodium adsorption ratio; SLRspatial linear regression; SP, saturation percentage; SSMU, site-specific management unit; TDR, time domain reflectometry; USDA-ARS, United States Department of Agriculture-Agricultural Research Service ∗ Corresponding author. Tel.: +1 951 369 4819; fax: +1 951 342 4962. E-mail address: [email protected] (D.L. Corwin). 0168-1699/$ – see front matter. Published by Elsevier B.V. doi:10.1016/j.compag.2004.11.002 104 D.L. Corwin, S.M. Lesch / Computers and Electronics in Agriculture 46 (2005) 103–133 were presented. The developed protocols provide the guidelines to assure reliability, consistency, and compatibility of ECa survey measurements and their interpretation. Published by Elsevier B.V.