Nodulation, Dinitrogen Fixation, and Yield Improvement in Second‐Crop Soybean Cover‐Inoculated with Bradyrhizobium japonicum

Abstract

AbstractWhen soybean [Glycine max (L.) Merr.) is grown in soil containing few Bradyrhizobium japonicum (Kirch.) Jordon, the limited mobility of the symbiont results in the formation of a small number of nodules distributed mainly on the primary root of the plant near the inoculation point. The authors conducted a 3‐yr study aimed at increasing nodulation and N2 fixation in ‘Hodgson’ soybean as a second crop, by cover inoculating B. japonicum on the soil with irrigation water at the time of sowing or at the three‐node (V3) stage. Inoculation treatments were: (i) seed inoculation; (ii) cover inoculation at sowing; (iii) seed inoculation plus cover inoculation at sowing; (iv) cover inoculation at the V3 stage; (v) seed inoculation plus cover inoculation at the V3 stage; (vi) uninoculated control. The seed plus cover inoculation at sowing or the V3 stage produced, on the whole, the greatest nodulation, 1.4 to 2.4 times that for seed inoculation alone. The addition of cover inoculation at sowing increased seed yield by 50 g m−2 in 1985 and 90 g m−2 in 1986, regardless of whether the cover inoculation was performed at sowing or the V3 stage. In 1988, a year in which the soybean was sown about 1 mo later than in the previous years and subjected to higher temperatures, seed and cover inoculation increased N2 fixation and plant‐N concentration, but not yield.