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EM-38 (Geonics Ltd., Mississauga, Ontario, Canada) mounted on a nonmetallic cart that was pulled through the field with a four-wheeled all terrain vehicle. The ECa values were recorded with a data logger every second (1.5 m), and the location was geo-referenced using a Trimble GPS (Trimble Navigation, Sunnyvale, CA) that was differentially corrected to provide an accuracy of <1 m.

Survey data were analyzed using the ESAP-95 software package (Lesch et al., 2000). The ESAP-95 software package assesses the spatial dependency of the data, calculates soil sampling locations that best encompass the variability present in the field, and uses measured soil data from those locations and a stochastic calibration model to predict the spatial pattern of secondary soil properties. Soil properties measured were 1:1 soil:distilled water electrical conductivity (EC1:1) and pH (Smith and Doran, 1996), clay content (Kettler et al., 2001), and 2 M KCl extractable NO3-N (Keeney and Nelson, 1982). The ECa survey data and the output files of predicted secondary soil properties were used to generate spatial maps by kriging using the GS+ software package (Robertson, 2000).

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