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This article in CS

  1. Vol. 38 No. 4, p. 975-982
    Received: July 31, 1997

    * Corresponding author(s): rshibles@iastate.edu
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Soybean Sulfur and Nitrogen Balance under Varying Levels of Available Sulfur

  1. P. J. Sexton,
  2. N. C. Paek and
  3. Richard Shibles 
  1. Dep. of Agronomy, Iowa State Univ., Ames, IA 50011.



Protein quality of soybean [Glycine max (L.) Merr.] seed could be enhanced by increasing the concentration of S-containing amino acids. The N:S ratio of soybean seed tissue is an indicator of protein quality. The objective of this study was to compare N and S accumulation and distribution in the soybean plant under varying levels of S availability. Soil S levels were varied in two greenhouse trials and tissue S and N contents were monitored. A field experi~nent with 0 and 60 kg ha−1 applied S was also conducted. In the two greenhouse trials, seed yield, rate of dry matter increase, and rate of N accrual by shoots all increased at least five-fold as S availability increased from less than 15 (zero added S) to 60 mg available S per plant, but showed little response to higher levels of S. Rate of S accrual was strongly related to S availability. In the field trial, there were no responses to added S. Leaf, pod, and seed tissue appeared to accumulate S in proteins, whereas, root and stem tissue appeared to accumulate S as sulfate. Harvest index values for S were consistently less than those for N, indicating S is not remobilized to seed as efficiently as is N. Seed S:N ratio was linearly related to the rate of S versus N accrual on a whole-plant basis. We estimate that a 50% increase in the amount of S-containing amino acids in soybean seed may require a 65 to 80% increase in S accrual by shoots to satisfy the increased demand for S.

Journal Paper No. J-17335 of the Iowa Agric. and Home Econ. Exp. Stn., Ames, IA. This work was supported in part by a grant from the Iowa Soybean Promotion Board.

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