Desenvolvimento da nodulação e fixação simbiótica de nitrogênio em variedades de soja, em diferentes estádios do desenvolvimento da planta

A study on development of nodulation and nitrogen fixation in soybean varieties throughout the growing season was made during summer, of 1971. Results for nodulation are expressed in weight of nodules per plant, and number of nodule per gram. Acetylene reduction per gram of nodules expressed nitrogenase activity and consequent ability of the Rhizobium-soy bean associations to fix nitrogen in nodulated tissue. Determinations were made at four stages of plant development, respectively for plants 50, 65, 80 and 93 days old, for the following soybean varieties: Rampage, Corsoy, Amsoy 71, Beeson, Wayne, Calland, and Bonus. Plants were harvested from two localities of Purdue University Farm, West Lafayette, Indiana, U.S.A. In a number of soybean varieties plant age markedly influenced nodulation by increasing size of nodules, weight of nodules per plant, and influencing nitrogenase activity. The variety Wayne produced the largest nodules and had high nodule weight, while Amsoy 71 presented the smallest nodules during the entire season. Late varieties (Wayne, Calland, and Bonus) had higher weight of nodules per plant and larger nodules than early varieties (Rampage, Corsoy, Amsoy 71, and Besson). At 50 and 65 days after planting, acetylene reduction was greater in nodules of early varieties than in those of late varieties. The maximum amount of ethylene production for early varieties occurred 15 days earlier than for late varieties. It seems that nitrogen fixation follows plant development and is decreased at plant maturity. The correlations between nodule weight per plant and ethylene produced by nodules in early varieties varied from negative in young plants to positive in old plants showing an effect of aging in these varieties. The lower weight of nodules in younger plants was partially compensated by higher nitrogenase activity of these nodules. Late varieties only presented correlation (negative) between acetylene reduction and weight of nodules per plant. It appears probable that nodule surface area has some influence on the acetylene reduction assay.