Fertilizer nitrogen use efficiency by winter wheat in the Willamette Valley Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/jh343w97f

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  • Efficiency of nitrogen fertilizer uptake by soft white winter wheat (Triticum aestivum L.) was measured over two cropping seasons across a range of soils and cropping histories in the Willamette Valley. Fate and potential losses of applied nitrogen were also assessed over a seventeen month period. In both cropping seasons, ¹⁵N labeled nitrogen was used to obtain a direct assessment of fertilizer nitrogen use efficiency (NUE), and to follow the distribution of fertilizer N in plant and soil. Nitrogen rate experiments were used to obtain an indirect assessment of NUE by regressing total N uptake on fertilizer N applied. Plant uptake of applied N ranged from 42 to 67%, with sites having poor soils or high root disease potential giving the lowest efficiencies. Direct assessment of uptake efficiency with N was more precise than indirect assessment, but was not necessarily more accurate. Recovery of fertilizer N in the grain ranged from 54% to 73% of the total fertilizer N taken up. Recovery in the grain was less the first year because of widespread leaf disease. Optimum economic N fertilization rates could be predicted (r² = 0.92) based on uptake of soil N and NUE. Availability of soil N was the most important parameter in determining optimum economic rate of N fertilization. Accountability of fertilizer N in plant and soil after the first crop ranged from 65% to 108% of that applied. Fertilizer N left in the soil was almost exclusively found in an organically combined form, primarily in the top 15 cm of soil. The contribution of residual fertilizer N to the following year's crop was minimal, but only half of the residual N was accounted for following the second crop. It appeared that 10 to 31% of the applied fertilizer N was lost between the end of the first cropping season and before the winter of the second cropping season. NUE by winter wheat in the Willamette Valley appears to be higher than NUE by dryland wheat grown in the Midwest. Sufficiently accurate assessment of NUE can be determined by indirect methods. This determination, combined with a method for determining soil N uptake, can contribute to improved N fertilizer recommendations for wheat in the Willamette Valley.
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