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THE 40 K and 214 BI (FROM 238 U) CONTENTS OF ROTHAMSTED SOILS DETERMINED BY GAMMA SPECTROMETRY
Author(s) -
SMITH G. J.,
TALIBUDEEN O.
Publication year - 1981
Publication title -
journal of soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.244
H-Index - 111
eISSN - 1365-2389
pISSN - 0022-4588
DOI - 10.1111/j.1365-2389.1981.tb01732.x
Subject(s) - radionuclide , soil water , potassium , soil test , environmental science , chemistry , calibration , phosphate , calibration curve , radiochemistry , environmental chemistry , soil science , detection limit , mathematics , physics , nuclear physics , chromatography , statistics , organic chemistry
Summary The gamma spectra of 17 surface soils from the Rothamsted Classical Experiments, selected for contrasting potassium and phosphate fertiliser treatments, were obtained to measure their contents of K and 214 Bi (from 238 U accumulated from phosphate fertilisers) contents, using the 40 K and 214 Bi photopeaks. The fate of the fertiliser residues are discussed for each Experiment, related to differences in fertiliser treatment and period of application. In 1978, potassium fertilisers increased soil K content by about 20% in Hoosfield (since 1852) and Barnfield (since 1843), and by about 7% in Broadbalk (since 1843). The K contents of the P and PNaMg plots in Barnfield suggest that Na substituted significantly for K in crop uptake. In Hoosfield and Barnfield (except the PK and PNaMg plots) phosphate fertilisers increased 2l4 Bi contents, but did not affect it in Broadbalk. A new method for the quantitative determination of the content of any radionuclide emitting gamma radiation, and whose photopeak can be clearly resolved in the gamma spectrum of the soil, is described. This involves measurements on the soil and on the calibration samples containing radionuclides other than those to be assayed, using the same ‘sample:detector’ geometry, and the establishment of a calibration curve with reference sources in an energy range suitable for interpolating the results for the energy of the radionuclide. The values thus obtained are shown to compare very favourably with a direct method in which standards containing various amounts of the test radionuclide are used to calibrate the equipment. By using 1 kg samples of < 2 mm soil non‐destructively, both methods avoid sampling errors and the need for finely ground (< 0.15 mm) soil inherent in conventional chemical analysis.