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Influence of Cultivar, Between-row Spacing, and Plant Population of Fixation of Soybean¹

An evaluation of the seasonal trends in nitrogen fixation by three soybean [Glycine max (L.) Merr.] cultivars differing in growth habits was made at two locations in Kansas. Two planting dates—May and June; two row spacings—38 cm and 76 cm—and two plant populations— 380,000 and 760,000 plants/ha were examined. Root samples were assayed weekly for acetylene reduction commencing from 3 weeks after planting until physiological maturity. The trends in N₂-fixation (acetylene reduction) for May and June plantings at both locations were similar for all cultivars, although more N₂ was fixed at the location where the soil was sandy and low in available soil N. There was a linear relationship between N accumulation and N₂-fixation. After pod filling Wiliiams (indeterminate) fixed more N₂ than the other cultivars. Elf (determinate) was consistently low in N₂-fixation ability throughout the sampling period. There was a significant positive response in Nrfixation to higher plant population at both locations. However, the effect of plant population was not evident in increasing total plant N uptake, seed N, or seed yield. The eariy planting date favored N₂-fixation by allowing a longer period of active fixation but showed no advantage in seed yield or total N accumulation.

Key Words: Nitrogen accumulation • Irrigation • Acetylene reduction

² 2 National Cereal Res. Inst. Moor Plantation, Ibadan, Nigeria (formerly graduate student): graduate student; associate professor of plant breeding, Dep. of Agronomy, Univ. of Illinois, Urbana, IL 61801, (formerly soybean geneticist): graduate student; and assistant professor of Biochemistry.

Received for publication November 14, 1979.

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				S. A. Ennin and M. D. Clegg Effect of Soybean Plant Populations in a Soybean and Maize Rotation Agron. J., March 1, 2001; 93(2): 396 - 403. [Abstract] [Full Text] [PDF]