Site-specific management (SSM) can potentially improve both economic and ecological outcomes in agriculture. Effective SSM requires strong and temporally consistent relationships among identified management zones; underlying soil physical, chemical, and biological parameters; and crop yields. In the central Great Plains, a 250-ha dryland experiment was mapped for apparent electrical conductivity (EC a). Eight fields were individually partitioned into four management zones based on equal ranges of deep (EC DP) and shallow (EC SH) EC a (approximately 0-30 and 0-90 cm depths, respectively). Previous experiments documented negative correlations between ECSH and soil properties indicative of productivity. The objectives of this study were to examine EC SH and EC DP relationships with 2 yr of winter wheat ( Triticum aestivum L.) and corn ( Zea mays L.) yields and to consider the potential applications of EC a-based management zones for SSM in a semiarid cropping system. Within-zone wheat yield means were negatively correlated with EC SH ( r=-0.97 to -0.99) and positively correlated with EC DP ( r=0.79-0.97). Within-zone corn yield means showed no consistent relationship with EC SH but positive correlation with EC DP ( r=0.81-0.97). Equal-range and unsupervised classification methods were compared for EC SH; within-zone yield variances declined slightly (0-5%) with the unsupervised approach. Yield response curves relating maximum wheat yields and EC SH revealed a boundary line of maximum yield that decreased with increasing EC SH. In this semiarid system, EC SH-based management zones can be used in SSM of wheat for: (i) soil sampling to assess residual nutrients and soil attributes affecting herbicide efficacy, (ii) yield goal determination, and (iii) prescription maps for metering inputs.
