Even though oats are not a typical crop in the North Platte River Valley, they were planted on the entire irrigated farmland (except the Illinois field) in spring 2003 because of their sensitivity to the kind of soil variability that also directly impacts yield variability. Visual comparison of the yield and ECa maps (Figure 20.2) shows similarities in some location-specific patterns (a positive correlation between the two), implying that the yield response was soil related.

Results from the yield and ECa mapping for the irrigated fields at SAREC are summarized in Table 20.1. Mean yield and coefficient of variation (CV) across all fields were 2206 kg/ha (ranging from 167 to 6379 kg/ha) and 39 percent, respectively. The yield map obtained from the yield monitor data identifies areas of high and low yield potential (Figure 20.2b). As shown, yield variability was significant even within individual fields as small as New Hampshire (7.5 ha). Mean ECa for the top 0.9 m soil and across all fields was 34.8 mS/m (milli Siemen per meter), ranging from 0.4 to 300 mS/m. Regardless of the size of the field, soil ECa showed high variability (Table 20.1), with an overall CV of 56 percent. The highest ECa values were observed in Illinois (mean of 50.6 mS/m), which also had the highest clay (21 percent) and organic matter (1.46 percent) contents. As expected, the lowest ECa values in Montana (mean of 22.7 mS/m) corresponded to the lowest clay (14 percent) and organic matter (1 percent) contents. The California field contains a saline seep (saturated paste EC = 1420 mS/m) near the southern tip of the field, clearly identified by the ECa mapping with

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