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Spatial Variability of Nitrogen‐15 Natural Abundance
Author(s) -
Sutherland R. A.,
Kessel C.,
Pennock D. J.
Publication year - 1991
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1991.03615995005500050024x
Subject(s) - spatial variability , transect , semivariance , geostatistics , soil science , environmental science , mathematics , statistics , ecology , biology
The primary objective of this study was to investigate the spatial variability of 15 N natural abundance (δ 15 N) in a non‐N 2 ‐fixing plant ( Triticum aestivum L.) on two fields. Two center intersecting 50‐point perpendicular transects were sampled on two separate fields, on Klassen (Udic Boroll) and Kruger (Typic Boroll) soils in Saskatchewan, Canada. Autocorrelation and semivariograms were used to assess the spatial structure of δ 15 N. Data from the Klassen field indicated that variation in grain δ 15 N was random, with no spatial structure at the scale of investigation (2–50 m). The pooled mean grain δ 15 N value and 95% confidence band was 5.43 ± 0.10‰, with a coefficient of variation of 8.9%. Observed variability in δ 15 N was primarily accounted for by analytical error in the Klassen field. The range in δ 15 N values for Klassen was 2.80‰, and the maximum difference between samples separated by 2 m was 2.00‰. These data indicate that, even in a low‐variability field, site‐to‐site variation may be significant. Thus, N 2 ‐fixing plants should be grown in close proximity to the reference crop for quantifying N 2 fixation. Spatial variability in δ 15 N for the Kruger field was significantly greater than in the Klassen field. Anisotropy was noted in δ 15 N in the Kruger field, with a pure nugget effect observed for one transect; for the other, a spherical model described the semivariance pattern with a range for spatial dependence of 16 m. The coefficient of variation and the minimum sample size required for estimating δ 15 N were corrected for the influence of serial correlation. Mean grain δ 15 N values for the two Kruger transects were 4.45 ± 0.13‰, and 4.29 ± 0.11‰. It is hypothesized that the greater variability in grain δ 15 N in the Kruger field resulted from a shorter lag time between fertilizer‐N application and sampling, that is 1.3 yr at Kruger, and 4 yr at Klassen.