Seasonal changes in growth and nodulation of perennial tropical pasture legumes in the field. III. Effects of flowering on nodulation of three Desmodium species

Abstract

Changes in plant dry weight, leaf weight, nodule weight per plant, nodule number and size, and nitrogen content of stem, leaf, and nodules were followed throughout the growing season in Desmodium sandwicense an indeterminate flowering type, D. uncinatum which flowers in April, and D. intortum which flowers in late May. The seasonal build-up and decline of the nodule population was not related to the onset of flowering, peak nodulation occurring 3 months before flowering in D. intortum and 1 month before in D. uncinatum. D. sandwicense had three flowering periods, with some loss of nodules after flowering, but in its general trend of build-up and decline was similar to the other species. Changes in nodule weight per plant were a function mainly of changes in nodule number. The relationship between loglo nitrogen yield per plant and nodule weight per plant was similar for the three species at early samplings, but at later samplings the nitrogen yield did not increase linearly with increases in nodule weight. Thus the regression coefficient could not be taken as a constant index of nitrogen-fixing efficiency for a species at all stages of growth.