Submitted to: Computers and Electronics in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/2004
Publication Date: 3/1/2005
Citation: Kaffka, S.R., Lesch, S.M., Bali, K.M., Corwin, D.L. 2005. Site-specific management in salt-affected sugar beet fields using electromagnetic induction. Computers and Electronics in Agriculture. 46:329-350. Interpretive Summary: Site-specific crop management depends on the ability to characterize the spatial variability of those soil physical and chemical properties that influence within field variation in yield that is less than maximum. The measurement of apparent soil electrical conductivity (ECa) with non-invasive electromagnetic induction (EMI) is one excellent means of characterizing soil spatial variability. To test the use of EMI for characterizing spatial variability and for assessing sugar beet yield, three sugar beet crops were grown on salt-affected fields in the Imperial and San Joaquin Valleys where EMI surveys were conducted. EMI was found to be 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.
Technical Abstract: Electromagnetic induction (EMI) was used to create geo-reference assessments of apparent soil electrical conductivity (ECa) and correlated soil properties in salt-affected fields in the Imperial and San Joaquin Valleys. Three sugar beet crops were grown and root and gross sugar yields evaluated at the field scale using a yield monitor and in subplots 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 Imperial Valley field overall, salinity increased with depth, indicating leaching of salts. The natural logs of electrical conductivity (ECe) and saturation percentage (SP) were strongly correlated with measured ECa (r = 0.97, r = 0.86) and nitrate was moderately correlated (r = 0.55). Root sugar yields declined at the higher salinity levels from 1 8.0 ti 8.0 Ng ha-1. The San Joaquin Valley 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, EM is useful for estimating optimum fertilizer N application rates 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.