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Nitrogen-15 Recovery in Winter Wheat as Affected by Application Timing and Dicyandiamide
- Bronson, K. F., Touchton, J.T., Hauck, R. D., Kelley, K. R.
- Soil Science Society of America journal 1991 v.55 no.1 pp. 130-135
- Paleudults, application timing, autumn, denitrification, dicyandiamide, grain yield, isotope labeling, leaching, loamy sand soils, nitrification inhibitors, nitrogen, nitrogen fertilizers, roots, spring, stable isotopes, straw, urea, winter wheat
- Nitrification inhibitor amendment to fall-applied N for winter wheat may reduce denitrification and leaching losses of N by maintaining N in ammoniacal form. A field study on a Norfolk loamy sand (fine-loamy, siliceous, thermic Typic Paleudult) compared fall application of ¹⁵N-labeled urea with and without dicyandiamide (DCD) and split urea application in fall and spring. Grain yield (mean 4.26 Mg ha⁻¹) increased with N rate (67, 101, and 134 kg N ha⁻¹), but was not affected by DCD or time of N application. Recovery of ¹⁵N in wheat the first year (mean 53%) was not affected by DCD or time of N application. Immobilization of ¹⁵N was 21, 20, and 15% with the fall N plus DCD, split-applied N, and fall N treatments, respectively. Nitrogen-15 leached at harvest was less with fall N plus DCD or split-applied N than with fall N only. Denitrification estimates, calculated as ¹⁵N not accounted for, were not affected by DCD or timing of N. In the second year, 101 kg N ha⁻¹ of unlabeled urea was split applied across the entire experiment. Grain yields averaged 2.07 Mg ha⁻¹ and were not affected by N rate, DCD, or timing of N application from the previous year. Percent recovery of ¹⁵N averaged 1.0 and 0.9% in the grain and straw, respectively, or about 10% of the ¹⁵N immobilized the year before. Recovery of ¹⁵N in the second year was significantly higher in the straw and roots following split-applied N or fall N plus DCD, compared with following fall N alone. This suggests that nitrification inhibitors can affect N uptake of a second-year crop by enhancing biological immobilization of fertilizer N.