Nodule development and nitrogen fixation in cultivars of Phaseolus vulgaris L. as influenced by planting density

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Abstract
Three cultivars of P. vulgaris, tested 39 and 69 days after planting, differed in the extent to which nitrogen (C2H2) fixation and nodule development were affected by plant density.At the 39-day harvest the climbing cultivar P590 declined in fixation from 15·1 μmol C2H4 produced/plant/h at 8·5 plants/m2, to only 4·2 μmol C2H4 produced/plant/h at 41·5 plants/m2; while the prostrate P498 showed consistently high fixation from 8·5 to 41·5 plants/m2. Variation in nitrogen fixation could be explained largely by change in nodule weight, though specific nodule activity (SNA) was affected, particularly in the cultivar P590. Since the percentage soluble carbohydrate in nodules of two varieties increased at certain planting densities while SNA decreased, some nodule dysfunction is possible.Density changes affected leaf, root and stem development in all cultivars, leaves on the lower nodes being most severely affected.At the 69-day harvest two varieties were advanced in filling the pods and showed poor nodulation and limited fixation, even at the widest plant spacings, while nodulation and nitrogen (C2H2) fixation in the third variety, which had just flowered, showed optima similar to the earlier harvest.