APPLICATION OF PLANT GROWTH-PROMOTING RHIZOBACTERIA TO SOYBEAN (GLYCINE-MAX [L] MERR) INCREASES PROTEIN AND DRY-MATTER YIELD UNDER SHORT-SEASON CONDITIONS

We previously reported that application of plant growth-promoting rhiz obacteria (PGPR) increased soybean growth and development and, specifi cally, increased nodulation and nitrogen fixation over a range of root zone temperatures (RZTs) in controlled environment studies. In order to expand on the previous studies, field experiments were conducted on two adjacent sites, one fumigated with methyl bromide and one nonfumi gated, in 1994. Two experiments were conducted at each site, one invol ving combinations of two soybean cultivars and two PGPR strains, the o ther involving the same factors, but also in combination with two stra ins Bradyrhizobium japonicum. Soybean grain yield and protein yield we re measured. The results of these experiments indicated that co-inocul ation of soybean with B. japonicum and Serratia liquefaciens 2-68 or S erratia proteamaculans 1-102 increased soybean grain yield, protein yi eld, and total plant protein production, compared to the nontreated co ntrols, in an area with low spring soil temperatures. Interactions exi sted between PGPR application and soybean cultivar, suggesting that PG PRs applied to cultivars with higher yield potentials were more effect ive. PGPRs applied to the rhizosphere without addition of B. japonicum also increased only leaf area and seed number at the fumigated site. Overall, inoculation of soybean plants with PGPRs in the presence of B . japonicum increased soybean grain yield, grain protein yield, and to tal plant protein production under short season conditions.