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This article in SSSAJ

  1. Vol. 57 No. 1, p. 169-178
     
    Received: Dec 31, 1991


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doi:10.2136/sssaj1993.03615995005700010031x

Landscape-Scale Variations in Plant and Soil Nitrogen-15 Natural Abundance

  1. R. A. Sutherland,
  2. C. van Kessel ,
  3. R. E. Farrell and
  4. D. J. Pennock
  1. Dep. of Geography, Univ. of Hawaii at Manoa, Honolulu, HI 96822
    Dep. of Soil Science, Univ. of Saskatchewan, Saskatoon, SK S7N 0W0, Canada

Abstract

Abstract

Although spatial variability in the 15N natural abundance in soils (δ15Nsoil) and plants (δ15Nplant) has been observed, the controls on this variability remain poorly understood. This study was conducted to assess landscape-scale patterns of δ15N in plant and soil and the topographic and pedological factors that control this variability. Two sampling grids (11 by 11 m and 110 by 110 m), each consisting of 144 sample points, were established in an irrigated field in southern Saskatchewan. The soils are dominantly Aridic Haploborolls (i.e., Orthic Brown Chernozems). Soil samples from both grids, and durum wheat (Triticum durum Desf.) from the large grid, were analyzed for δ15N. Spatial statistical analysis indicated that δ15Nsoil exhibited a random pattern in the small grid. In the large grid, however, δ15Nsoil and δ15Nplant exhibited depression-centered patterns that were similar to those observed for denitrification activity and related soil properties. Variability was greater for δ15Nplant than for δ15Nsoil and the extreme outliers for δ15Nplant were associated with the landform elements with the highest denitrification activity and lowest Eh values (<310 mV). The extreme variability in δ15Nplant was attributed to the greater susceptibility of the small mineral-N pool (2% of the total soil N) to biological activity and concomitant N-isotope fractionation than the larger and more inert total soil organic-N pool. The data indicate that (i) topography had a significant influence on the landscape-scale patterns of δ15Nsoil and δ15Nplant, and (ii) δ15N (soil and plant) and the soil variables that controlled denitrification activity followed similar patterns in the landscape.

Contribution no. R700 of the Saskatchewan Institute of Pedology.

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