Nodulating and Non-nodulating Lee Soybean Isolines Response to Applied Nitrogen1
- M. S. Bhangoo and
- 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.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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