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This article in AJ

  1. Vol. 67 No. 2, p. 265-268
    Received: May 23, 1974

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Indexes of Sulfur Deficiency in Alfalfa. II. Plant Analyses1

  1. D. T. Westermann2



Both soil and plant analysis are diagnostic tools used in identifying S deficiencies; however, soil tests evaluating soil S availability levels are not always successful and deficiencies must then be identified by plant analysis. In addition, the diagnostic tool must be correlated to crop responses under various growing conditions to be useful. Identification of S deficiency on alfalfa (Medicago sativa L.) in southern Idaho permitted the collection of correlation data for both S soil tests and plant analyses. The S soil test correlation data has been previously reported (Agron. J. 66:578–581, 1974). This paper reports the relationships found between the plant S indexes of total S, SO4-S and total (N/S) ratio, and the response of alfalfa to S fertilization. All data were evaluated by correlation analyses.

The total S and SO4-S concentrations and the total (N/S) ratio were all found to be satisfactory indexes of S deficiency in whole alfalfa at early bloom. Maximum forage yields were obtained when the tops contained between 0.15 to 0.20% S or 0.05% SO4-S. Total S and SO4-S were related and readily interchangeable as indexes. Increases in total S above 0.14% S resulted from the accumulation of SO4-S. Yield responses to S fertilization were obtained when the total (N/S) ratio was greater than 17 to 18. Total N and total S were not related, but protein N increased linearly as protein S increased. The protein (N/S) ratios were not constant and increased from 17 to 23 as the degree of S deficiency increased.

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