Site-specific management in salt-affected sugar beet fields using electromagnetic induction

An assessment of field-scale variation and the characterization of correlated crop response are the first steps in evaluating the potential for variable-rate technologies and other techniques used in site-specific management (SSM). The responses of sugar beets to salinity and to residual and applied soil N were studied at sites in California's Imperial and San Joaquin Valleys to evaluate the potential of electromagnetic induction (EMI) techniques for SSM. Electromagnetic induction was used to create geo-referenced assessments of apparent soil electrical conductivity (ECa) and correlated soil properties in salt-affected fields in the Imperial (IV) and San Joaquin (SJV) Valleys. Soils at the two sites were primarily fine, smectitic (calcareous) thermic, vertic Torifluvents and Fluvequents, respectively. Two crops were grown in the IV and one in the SJV. Root and gross sugar yields were evaluated at field scale using a yield monitor and in subplots centered on soil sampling locations chosen using ESAP-95 (v. 2.01) software that were harvested by hand. Average subplot root yields differed from field-scale averages derived from the yield monitor by less than 4% for all three crops. In the IV field, average salinity increased with depth, indicating leaching of salts. The natural logs of electrical conductivity of the saturation paste extract (ECe) and saturation percentage (SP) were strongly correlated with measured ECa (r=0.97 and r=0.86, respectively) and nitrate was moderately correlated (r=0.55). Root and sugar yields declined at the higher salinity levels from 18.0 to 8.0 mg ha(-1). The SJV site was poorly drained and leaching was not apparent. ECe was strongly correlated with ECa (r = 0.94), but SP was not (r = 0.20). Gross sugar yields apparently were influenced by SP rather than by ECe and varied from 2.9 to 14.1 mg ha(-1). Where crop growth and yield are influenced by salinity, EMI is useful for estimating optimum fertilizer N application rates and for identifying areas of the field that will have unprofitable yields. Irrigation might be withheld from these areas and the water saved for other beneficial uses. (c) 2004 Published by Elsevier B.V.