Root length, Nodulation and Biological Nitrogen fixation of Rhizobium inoculated soybean (Glycine max [L.] Merr.) grown under maize (Zea mays L.) intercropping systems and P and K fertilization

摘要

A two years field trial was carried out to investigate the effects of Rhizobium inoculation supplemented with P and K on root length, nodulation and N 2 -fixation in soybean intercropped with maize. The split-split plot design with 2 x 4 x 7 factorial arrangement replicated thrice was used. The main plots had two rhizobial inoculation treatments, while the sub plots comprised of four cropping systems namely Maize (sole crop), Soybean (sole crop) and two intercropping at different spacing. The sub-subplots were assigned to fertilizer levels (kg ha -1 ): control; 20K; 40K; 26P; 52P; 26P + 20K; 52P + 40K. Dried plant sample were ground for determination of N 2 -fixation. N 2 -fixation was estimated using total nitrogen difference method where the total nitrogen obtained from none-fixing plants (Maize) was subtracted from total nitrogen obtained from fixing plants (Soybean). The results revealed that cropping systems, Rhizobium inoculation and P and K fertilizers have differently affected the root length, number of nodules and/or nitrogen fixation in soybean. Intercropping increased the number of nodules relative to sole soybean. Inoculated soybean significantly increased root length, number of nodules and nitrogen fixation over un-inoculated. Root lengths were increased by 7.5% and 7.3% in 2015 and 2016 respectively. P and K fertilization also increased the number of nodules and nitrogen fixation over the control. There was also a significant interaction of Rhizobium inoculation and fertilizers on number of nodules and nitrogen fixation in 2015 cropping season. The use of combined fertilizers at lower rates (20K+26P) was generally seen to be better.