Comparative nodulation, nitrogen fixation, and growth of Glycine wightii cv. Cooper and Phaseolus atropurpureus cv. Siratro seedlings

Abstract

The growth, nodulation, and nitrogen fixation of Glycine wightii cv. Cooper (Glycine) and Phaseolus atropurpureus cv. Siratro (Siratro) were compared in a glasshouse, sand culture techniques being used in a series of trials encompassing a full range of seasonal environments. Plants were inoculated with the commercial Rhizobium strain (CB756) for both species either at germination or 12 days later when seed reserves were virtually exhausted.

In both early and late inoculation treatments, Siratro nodulated and established nitrogen fixation more rapidly than did Glycine. This difference between the species was not directly associated with the marked difference in seed size.

When active nitrogen fixation was fully established, the disadvantage shown by Glycine in the early nodulation phase was not evident, and the treatments were similar in the rate of growth and nitrogen accumulation, proportion of nodule weight to whole plant weight, proportion of pigmented nodules, efficiency of nitrogen fixation, and concentration of nitrogen in the whole plant.

The relatively slow initial nodule development in Glycine is probably one of the important factors hindering the field establishment of seedlings, but in subsequent growth the symbiosis appears fully effective.