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Fluid Journal : Fluid Journal 1996-1998
1 Fluid Journal Summer 1998 Summary: Corn yield varied widely along the landscapes. Corn yields of the unfertilized strips described the variations in soil properties over the landscapes. Higher yields were associated with topographically lower depositional areas having higher soil organic matter content and available N, and lower soil pH and lime contents. Soil profile NO3-N varied 300 percent at the Sterling site and 1,200 percent at the Stratton site. The lowest residual NO3-N levels were found on eroded sideslopes. Very high residual NO3-N levels (up to 225 lbs/A of N) were found on the toeslopes at the Stratton site, with all other positions having low values. Soil properties were used to develop a "soil index," which identified those factors that positively and negatively impact Weld. Soil index value correlated positively with corn yield, explaining about 58 percent of the total variability in corn yields. Results of this study show promise for improving N fertilizer recommendations in dryland corn either under conventional or VRT soil fertility management. However, many factors affect crop Weld in addition to soil test parameters. The more of these that can be considered, the greater the probability of success of VRT programs. Recent results from precision agriculture research have shown the yield variability within a field is much greater than we previously thought. The big question is "why do these yield variations occur and what can we do to impact them?" Large and continuous variability in soil properties and corn yields found on typical landscapes of eastern Colorado provides an excellent opportunity to study the relationships between grain yield and soil properties affecting productivity. From this, we hope to develop guidelines for N fertilizer recommendations for dryland corn that can be used in precision agriculture or variable rate fertilizer technology (VRT). The use of the field average for a Drs. R.A. Ortega, D.G Westfall, and G.A. Peterson; W.J. Gangloff Soil Variability In Landscapes Affects N Management Colorado researchers find topographical variability affects grain yield, soil properties, and N fertilizer response of dryland corn in VRT studies. yield goal to estimate N fertilizer needs under VRT is not an accurate method where factors other than soil-available N control yields. Yield maps obtained with a yield monitor may be able to produce "site specific" N fertilizer recommendations within a field when used with the appropriate algorithm. However, this approach assumes that yield goal is an adequate representation of spatial nutrient needs, that yield goal can reflect N fertilizer-use efficiency, and only N is the limiting growth factor. This report covers our precision agriculture research on spatial variability of soil N components and Figure 1. Spatial variability of corn grain yields of two N treatments, Sterling, CO, 1996 (30, 60 and 90 lbs/A rates are not shown due to data overlap).
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