N.J. BRANDON¹, R.A. DATE¹, R.L. CLEM², B.A. ROBERTSON³ and T.W.G. GRAHAM⁴

¹CSIRO Tropical Agriculture, Brisbane, Queensland, Australia
²Department of Primary industries, Brian Pastures Research Station, Gayndah, and
³Roma Research Station, Roma, and
⁴Rockhampton, Queensland, Australia

Abstract

Growth of Desmanthus virgatus cvv. Marc, Bayamo and Uman, inoculated with Rhizobium strain CB3126, was compared with that of uninoculated and inoculated + nitrogen-fertilised plants at 4 sites in south-east Queensland over a 3-year period. Supplementary irrigation was used to ensure prompt establishment. The proportion of nodules due to the inoculum strain was determined using serological methods and the proportion of total plant nitrogen arising from biological fixation in the second and third years was estimated using the natural abundance method.
Top growth was increased significantly by inoculation at 3 sites in the first year and at 1 site in the second year. Growth increases relative to uninoculated plants varied from 34–313% and appeared to depend on the prevalence of indigenous strains and soil nitrogen level. The inoculum accounted for few (< 3%), some (0–65%) or most (> 94%) of the nodules formed in soils in which nodulation of uninoculated plants was high, medium and low, respectively. The proportion of total nitrogen due to biological nitrogen fixation in the second and third years ranged from 0% in a highly fertile soil to 38–98% in 3 soils of low-moderate fertility.
The ability of strain CB3126 to increase growth of desmanthus in some soils was confirmed in these field trials. Inoculation of desmanthus seed with an effective strain of Rhizobium such as CB3126 is recommended.