RESUMO
This research was aimed at obtaining varieties of soybean adaptive to acid soils and to obtain Plant Growth-Promoting Rhizobacteria (PGPR) isolates that can improve the agronomic characteristics of soybean and increase the ultisols fertility. This research was conducted in two-stages research on Sampali Village, Percut Sei Tuan sub-District, Deli Serdang District, North Sumatra Province, Indonesia from August 2019 until March 2020. The first stage (adaptive varieties screening) using the non-factorial Randomized Block Design (RBD) with the varieties of Argomulyo, Wilis, Kaba, Dena-1, Devon-1, Dega-1, Demas-1, Burangrang, Detam-1, and Kipas Merah. The second stage (application of PGPR isolates singly and in combinations) using the factorial RBD, the first factor of applicative single and the combination of PGPR isolates, the second factor of adaptive varieties including Detam-1 and Wilis. Data were analyzed with ANOVA and followed by DMRT at P<0.05. The results showed that the Detam-1 and Wilis varieties had significantly higher yield per plant of 14.73 g and 14.54 g, respectively, than other varieties. The applications of a single and combination of PGPR isolates significantly increased the number of branches, stem diameter, plant height, yield per plant, soil pH, organic-C, available-P, and total-N and decreased the soil C/N. The Detam-1 variety had the higher in yield per plant compared to Wilis variety. The isolates combination of Rhizobium leguminosarum+Rhizobium sp2+Bacillus sp+Burkholderia sp for Detam-1 and Wilis varieties can be recommended to support the growth and yield of soybean on ultisols.
