Effects of Acid Soil Infertility Factors on Growth and Nodulation of Soybean1

Abstract

AbstractGrowth of a legume in acid soils can be limited by the effects of infertility factors on the growth of the host plant per se or on nodulation and nodule function. Effects of varying solution pH (4.5, 5.0, 5.5) and external calcium (Ca) concentration (0.05, 0.5, 2.5 mM) on growth and nodulation of soybean [Glycine max (L.) Merr. cv. Fitzroy] were investigated in a solution culture experiment. Total dry matter production was not influenced by pH; however, shoot growth increased while root growth decreased with increasing solution pH. Increase in Ca concentration significantly increased shoot dry weight at pH 5.0 and 5.5. At pH 4.5, appearance of the first nodule was delayed, and nodule number and nodule dry weight per plant were lower than at higher pH. Nodule number and dry weight per plant were not affected by Ca concentration at pH 4.5 but increased significantly with increasing Ca concentration at pH 5.0. At pH 5.5, nodule number per plant decreased, but nodule dry weight increased as Ca concentration increased from 0.5 to 2.5 mM. Further experiments were conducted at pH 4.5 with 0.5 mM Ca concentration to investigate the effects of monomeric aluminum (Al) activity (∑ aA1 mono) on the growth of soybean supplied with adequate inorganic N and on growth and nodulation of plants inoculated with Bradyrhizobium japonicum. Shoot and root weights declined linearly with increase in ∑ aAl mono, with the critical ∑ aAl mono (90% of yield in Alfree treatment) ranging from 5 to 9 µM. Nodulation was totally inhibited in solutions with ∑ aAl mono ≥ 27.8 µM. The critical ∑ aA1 mono for nodule number and for nodule dry weight per plant were approximately 0.4 µM.