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Using Electrical Conductivity Classification and Within-Field Variability to Design Field-Scale Research

^a USDA-ARS, 119 Keim Hall, Lincoln, NE 68583-0934
^b Univ. of Nebraska, 103 Miller Hall, Lincoln, NE 68583
^c Colorado State Univ., C130 Plant Sci., Ft. Collins, CO 80523
^d Usda-Ars, Aerc-Csu, Ft. Collins, Co 80523-1325

View larger version (43K): [in a new window]   Fig. 1. Experimental layout for 1999. The 250-ha experimental site is subdivided into eight approximately 31-ha fields. Two replicates of each phase of the winter wheat (W), corn (C), proso millet (M), and fallow (F) rotation are represented each year. The entire site is managed under no-tillage.

View larger version (130K): [in a new window]   Fig. 2. An interpolated and classified electrical conductivity map (12 classes determined by unsupervised classification) for the field located in (A) the northwest corner of the experimental site and (B) the same map following recoding into four electrical conductivity classes. Variations in color, from dark to light, correspond to increasing conductivity, and the symbols represent selected soil-sampling sites. Ranges of apparent electrical conductivity for each of the four classes from low to high are 0 to 0.17, 0.17 to 0.23, 0.23 to 0.29, and 0.29 to 0.56 dS m-1.

View larger version (84K): [in a new window]   Fig. 3. Relationship between apparent electrical conductivity (ECa) classification and plot-scale blocking (replication). (A) An aerial photograph of the experimental site with an example of a plot-scale experiment in the center of the southeast field, (B) an ECa–classified map of the field, and (C) the plot-scale experimental site identified within the field using ECa classification as a basis for blocking.