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United States Department of Agriculture

Agricultural Research Service

Research Project: SOIL CONSERVATION SYSTEMS FOR SUSTAINABILITY OF PACIFIC NORTHWEST AGRICULTURE

Location: Land Management and Water Conservation Research

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

Authors
item Pan, William - WSU
item Schillinger, William - WSU
item Huggins, David
item Koenig, Richard - WSU
item Burns, John - WSU

Submitted to: Proceedings of the Soil Science Society of America
Publication Type: Literature Review
Publication Acceptance Date: August 10, 2007
Publication Date: October 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: 9/22/2014
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