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Sulfur Diagnostic Criteria as Affected by Age and Defoliation of Subclover
Author(s) -
Jones M. B.,
Ruckman J. E.,
Williams W. A.,
Koenigs R. L.
Publication year - 1980
Publication title -
agronomy journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 131
eISSN - 1435-0645
pISSN - 0002-1962
DOI - 10.2134/agronj1980.00021962007200060042x
Subject(s) - trifolium subterraneum , sowing , sulfate , agronomy , biology , trifolium repens , zoology , grazing , chemistry , pasture , organic chemistry
Sulfur deficiencies are widespread in California annual grasslands and in other areas of the world where subclover ( Trifolium subterraneum L.) is an important legume. Intensive grazing is often practiced where subclover is grown. Therefore, to determine the need for S fertilization it is important to know how defoliation and plant age influence the diagnostic tissue tests used to assay subclover S status. Subclover was grown on S−deficient soil (Josephine, fine−loamy, mixed mesic, Typic Haplozerults) with six levels of applied S and four clipping treatments in a greenhouse. Four criteria for assaying S status were used: total S, sulfate S, sulfate S/total S ratio, and N/S ratio in the three youngest fully expanded leaves required to give 90% of maximum yield (critical levels based on Mitscherlich functions). The critical levels of sulfate S/total S and N/S ratios were the most stable over plant age and clipping frequency. Both assays accounted for about three−quarters of the variation on the average. The critical levels of total S and sulfate S although associated with over 90% of the variation were not stable individually, decreasing from 0.20 to 0.08% S and from 220 to 140 pprn sulfate S at 60 and 133 days from planting, respectively. Clipping frequency caused considerable variation in the critical levels for total S and sulfate S assays, making them more difficult to interpret than the sulfate S/total S and N/S ratio assays. It was concluded that the sulfate S/total S ratio has some advantages over the other assays, such as stability through the growing season, being little affected by defoliation, and resulting from a single analytical regime.