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Dinitrogen Fixation by Soybeans in Alabama

Thurlow, D. L., Hiltbold, A. E.
Agronomy journal 1985 v.77 no.3 pp. 432-436
Glycine max, nitrogen fixation, Alabama
The contribution of symbiotic N₂ fixation to total N and yield of soybeans [Glycine max (L.) Merr.] ranges widely among soils and cultural conditions. Utilization of nonnodulating soybean isolines and ¹⁵N-dilution techniques has provided estimates of fixation in indeterminate cultivars on soils of relatively high N supply. Few estimates are available, however, for determinate soybeans on low N soils of the southeastern United States. This work compared the N assimilation of ‘Lee’ soybean with that of its nonnodulating isoline (N-N Lee) at 10 locations in Alabama over an 8-year period. Nitrogen accumulations by higher yielding cultivars were also determined. Dinitrogen fixation was estimated as the difference in the amount of N contained in N-N Lee and Lee or other fixing cultivar. One approach considered N in harvested beans only while another approach involved total N in aboveground plant material at physiological maturity. Results showed that Lee soybeans grown in Alabama without irrigation but with rainfall sufficient for yields exceeding 1640 kg ha⁻¹ fixed an average 172 kg ha⁻¹ of N, while maximum yielding cultivars fixed 217 kg ha⁻¹ of N in aboveground plant material. The estimate for midwestern soybeans of 40% of plant total N derived from the atmosphere is too low for Alabama soybeans, where 70% or more is obtained by fixation.