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United States Department of Agriculture

Agricultural Research Service

Title: Fifty Years of Predicting Wheat Nitrogen Requirements Based on Soil Water, Yield, Protein, and Nitrogen Efficiencies)

Author
item Pan, William
item Schillinger, William
item Huggins, David
item Koenig, Richard
item Burns, John

Submitted to: Proceedings of the Soil Science Society of America
Publication Type: Literature Review
Publication Acceptance Date: 8/10/2007
Publication Date: 10/23/2007
Citation: Pan, W.L., Schillinger, W., Huggins, D.R., Koenig, R., Burns, J. 2007. Fifty Years of Predicting Wheat Nitrogen Requirements Based on Soil Water, Yield, Protein, and Nitrogen Efficiencies. Proceedings of the Soil Science Society of America.

Interpretive Summary: During the early 1950’s synthetic N fertilizers gained widespread adoption in the wheat growing region of the inland Pacific Northwestern U.S. Agronomists quickly recognized water and N as the two principal determinants of grain yield and quality. Consequently, many N fertility trials have been conducted across a range of environments, soils, and cropping systems and have provided the basis for N fertilizer recommendations based on yield-based crop N requirements, estimates of soil N supplies and N use efficiencies. This N recommendation model based on the regional variations in crop-soil N budgets has stood the test of time for nearly 50 years. We analyzed recent data to assess the applicability of the N recommendation model developed in the 1950’s not only for regional application, but also to produce site-specific N prescriptions. Stored soil water assessed in the spring remained a reasonable predictor of yield in this Mediterranean climate, but variable in-season rainfall is still a major source of error. In contrast, yield-water availability relationships were not well correlated in field-scale, site-specific scenarios. On a regional basis, the N recommendation model developed during the 1950’s is still applicable for current farm N management. On a site-specific field–scale, however, our inability to predict landscape processes that control the water-yield and the yield-nitrogen use relationships limits our ability to extrapolate the regional model to precision N applications.

Technical Abstract: During the early 1950’s synthetic N fertilizers were gaining widespread adoption in the wheat growing region of the inland Northwestern U.S. Agronomists quickly recognized water and N as the two principal determinants of grain yield and quality. Many N fertility trials across a range of environments, soils and cropping systems provided the basis for developing fertilizer recommendations based on yield-based crop N requirements, estimates of soil N supplies and N use efficiencies. This N recommendation model, based on the regional variations in yield-water relationships and crop-soil N budgets, has stood the test of time for nearly 50 years. Spring soil moisture remains a reasonable yield predictor in this Mediterranean climate, but variable in-season rainfall is still a major source of error. Adjustments in the N recommendation model have been made to accommodate differences in wheat class, soil characteristics, management practices and climatic factors that affect water and N use efficiencies. However, our ability to extrapolate the regional model to site-specific applications has been restricted by the inability to predict landscape-scale processes that control water redistribution, water-yield and yield-nitrogen use relationships that define the unit N requirement. The generalized 50% single season N uptake efficiency used in the model is not likely to occur consistently within a given field or from year-to-year and is currently under increased scrutiny in order to realize improvements in field-scale N management and N uptake efficiencies.

Last Modified: 8/24/2016
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