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Fluid Journal : Fluid Journal 1993-1995
3 Fluid Journal Summer 1994 found in the wheat-corn-fallow versus the wheat-fallow rotation in treatments receiving less N fertilizer due to the greater depletion of soil N in the more intense cropping system. Soil profile (0 to 6 feet) NO3-N data taken from Sterling in the fall of 1991 showed the same interaction with rotation and N fertilizer. Soil profile data from Stratton, however, did not exhibit this interaction. When comparing N-use efficiency of wheat, the wheat-corn-fallow rotation had greater N-use efficiency than the wheat-fallow rotation at both Sterling and Stratton. This effect can be attributed to the fact that wheat-corn- fallow soils are generally more N- depleted than wheat-fallow soils. At the Sterling location, as N rate in-creased, N-use efficiency decreased. This same trend was observed at Stratton. Comparison of N source/ placement effects on N-use efficiency revealed that UAN split application had significantly higher N-use efficiency than the other three application methods at Sterling. Applying N fertilizer in a band near the seed and over the row at planting consistently allowed the most efficient use of N. Besides being readily accessible to the plant, this application method more effectively avoids loss of N through immobilization and volatilization. Corn Corn grain yield and crude protein increased with N rate at both Sterling and Stratton. Although corn yields at Stratton were higher than at Sterling for the 70-and 105-lb/A rates of N, the overall aver-age yield at Sterling was slightly higher than at Stratton. Generally speaking, Sterling has outproduced Stratton in corn production when precipitation has been comparable at both sites. Dryland corn at both Sterling and Stratton averaged about 72 bu/A for the two highest N rates. Yield levels of the check plots (0 lbs/A of N) have been higher at Sterling (54.5 bu/A) than at Stratton (41.3 bu/A), indicating that soil N mineralization rates are greater at the Sterling location. Both sites, however, produced about one bu/A of corn for every one lb/A of N taken up by the plant. Differences among N source/ placement treatments were not distinct. UAN split treatment produced high yields at Sterling, but was the lowest yielding at Stratton. These results indicate that producers have some flexibility when choosing N application methods for dryland corn. Drs. Westfall and Peterson are professors of agronomy, and Kolberg is research assistant at Colorado State University; Sherrod is biological technician, Great Plains Systems Research Unit, Ft. Collins, CO.
Fluid Journal 1996-1998