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DIVISION S-8 - NUTRIENT MANAGEMENT & SOIL & PLANT ANALYSIS

Nitrogen and Water Stress Interact to Influence Carbon-13 Discrimination in Wheat

^a Plant, Plant Science Dep., South Dakota State Univ., Brookings, SD 57007
^b Land Resources and Environmental Sciences, Montana State Univ., Bozeman, MT
^c Northern Agricultural Research Center, Montana State Univ., Havre, MT 59501

* Corresponding author (david_clay{at}sdstate.edu)

The impact of interactions between water and N stress on ¹³C isotopic discrimination () is not well understood. The objective of this study was to determine the impact of N on in wheat (Triticum aestivum L.) grown under low, moderate, and high water stress. In a field study located near Havre, Montana, USA (48° 30' N lat. and 109° 22' W long.), wheat grown under three different water stress environments (low, moderate, and high) was fertilized with three different N rates (none, moderate, and high). Each treatment was replicated four times. The grain N fertilizer use efficiency increased as water stress decreased. A differential response of to N was observed. In general, if plants were grown under high water stress and N increased yield, then adding N to N-deficient plants reduced (-0.01 for every kg of N added); and if plants were grown under low water stress and N increased yield, then adding N had little or no impact on . The break point between N impacting or not impacting was 17.45. Under non-N limiting (moderate and high N) conditions the equation relating to yield was, yield (kg ha^-1) = -11000 + 884 , r = 0.92**. Wheat grown under N-deficient conditions (0N treatment) did not fit this curve. By accounting for the impact of water and N stress on , this variation could be explained. Results from this study suggest that can be used to characterize N and water stress at different landscape positions in watershed studies.

Abbreviations: , ¹³C isotopic discrimination • FUE, fertilizer use efficiency • OY, optimum yield • YLND, yield loss due to N deficiency • 0N, N-deficient conditions • **Siginificant at the 0.01 probability level