Key components of precision agriculture are (i) identifying the site-specific factors that influence within-field crop yield variation and (ii) spatially characterizing those factors. Geo-referenced measurements of apparent soil electrical conductivity (ECa) provide a potential means of characterizing the spatial variability of edaphic properties that influence crop yield. It is the objective (i) to utilize an intensive ECa survey to direct soil sampling, (ii) to identify soil properties that influence cotton yield, and (iii) to use this spatial information to make site-specific management recommendations to increase cotton yield. A 32.4-ha field in California’s San Joaquin Valley was used as a study site. Cotton yield monitoring data were collected in August 1999 followed by an intensive ECa survey of 4000 measurements using electrical resistivity. Sixty soil sample sites were selected based upon a responsesurface sampling design utilizing the spatial ECa measurements. Scatter plots were obtained and correlation and regression analyses were performed to assess the relationship between cotton yield and the properties of pH, boron (B), nitrate-nitrogen (NO3-N), chloride (Cl-), salinity (i.e., electrical conductivity of the saturation extract; ECe), leaching fraction (LF), water content (θg), bulk density (ρb), % clay, and saturation percentage (SP). Correlation coefficients of -0.01, 0.50, -0.03, 0.25, 0.53, -0.49, 0.42, -0.29, 0.36, and 0.38, respectively, were found. The correlation coefficient between yield and ECa was 0.51. A site-specific response model of cotton yield based on ordinary least squares (OLS) and adjusted for spatial autocorrelation using restricted maximum likelihood was developed. The response model indicated that leaching fraction, salinity, water content, and pH were the most significant soil properties influencing cotton yield: cotton yield (Mg ha-1) = 19.28 0.22 ECe – 0.02 ECe 2 – 4.42 LF2 – 1.99 pH 6.93 θg. The spatial information and response model provide sufficient information to make site-specific management recommendations to increase cotton yield.