Comparisons of nitrogen fixation estimates in soybeans by nodule weight, leghemoglobin content, and acetylene reduction

Abstract

Nodule leghemoglobin content, acetylene reduction rates, and nodule weight determinations were made during an entire growth period of soybean (Glycine max (L.) Merr. cv. Altona) plants grown under field conditions. High correlations within most sampling dates were found between each pair of possible comparisons of these indicators of nitrogen fixation.Rates of conversion of acetylene to ethylene per milligram leghemoglobin constantly decreased during the growing season, whereas leghemoglobin content per gram nodule fresh weight remained relatively constant. These results indicate that leghemoglobin content of nodules could be used to compare rates of nitrogen fixation in plants of a soybean cultivar at similar stages of development but should not be used to compare fixation rates in plants at different stages in ontogeny.