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This article in AJ

  1. Vol. 68 No. 4, p. 642-645
    Received: Sept 6, 1975

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Nodulating and Non-nodulating Lee Soybean Isolines Response to Applied Nitrogen1

  1. M. S. Bhangoo and
  2. D. J. Albritton2



Further studies on N fertilization of soybeans [Glycine max (L.) Merr.] were needed for better understanding the relative capacity of soybeans to fix atmospheric N and utilization of applied or soil N and fixed N. Field experiments with nod and non-nod Lee isolines were conducted for 3 years on a prelimed Calloway silt loam (fine-silty, mixed, and Thermic family of Glossaquic fragiudalfs). Nitrogen in the form of NH4NO3 at the rates of 0, 56, 112, 224, and 448 kg/ha was applied each year. Grain and vegetative matter yield, N content and total N uptake showed significant increases from applied N each year. Grain yields of nod Lee from the no-N treatments equalled those of the non-nod Lee at the 0 and 56 kg N/ha in 1973 and at the 112 and 224 kg N/ha rates in 1971 and 1972, respectively. Yields of both isolines were highest and similar at the 224 and/or 448 kg N/ha rates each year. Higher grain yield and total N uptake in the non-nod no N, 56, and 112 kg N/ha rates especially in 1973 indicated utilization of soil and applied N. Utilization of applied and soil N along with fixed N was evident in both isolines each year. Of the total N uptake, the amount of fixed N in the no-N treatments in 1971 and 1972 was 51.0 and 63.9%, respectively, and was 22.1% in 1973, possibly because of high residual soil N. Symbiotic N fixation decreased practically to zero when N rates exceeded 224 kg/ha. The 56 kg N/ha had little effect on N fixation. Applied or soil N along with fixed N appeared to be essential for maximum soybean yields on poorly drained soils low in organic matter with a strongly acid subsoil. Rates of N applied should be within the range where symbiotic fixation is not inhibited and should be based on the residual soil N.

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