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Tuesday - January 02, 2007

From: Leander, TX
Region: Southwest
Topic: Propagation
Title: Rhizobium inoculant for Leucaena and othr leguminous tree seedlings
Answered by: Nan Hampton and Joe Marcus

QUESTION:

What sort of Rhizobium inoculant would be appropriate for Leucaena and other leguminous tree seedlings?

ANSWER:

It is correct that legumes such as White Leadtree (Leucaena leucocephala) and, as another example, bluebonnets, require Rhizobium bacteria to enable them to fix atmospheric nitrogen for use by the plant. Furthermore, there are different strains of Rhizobium and the strains that are effective for bluebonnets are not necessarily effective for Leucaena. The Rhizobium strains are species specific. It is possible that the proper strain of Rhizobium is present in your soil already. You can check this by looking at the roots of your Leucaena. If there are nodules present, then it already has the correct Rhizobium species. If you have access to mature Leucaena plants, you can simply harvest some soil from around the roots of them and inoculate your seedlings' soil with some of it. It would only take a very small amount per pot. You could mix a handful or two of native soil into a pile of potting soil and that should do the trick—nothing fancy; the roots and the Rhizobium will find one another.

Research in Australia has cited two strains of Rhizobium that are effective with Luecaena. In acid soils Strain CB3060 (TAL1145) was most effective in N2 fixation. This is cited in Tolerance of Leucaena to Acid Soil Conditions by F.P.C.Blarney and E. M. Hutton, p.84. In the article "Establishment and Early Growth of Leucaena" C. M. Piggin et al., p. 87, report strain CB81 was found reliable and strain NGR8 less reliable. They also report (p. 88) CB3060 (TAL1145) is good in acidic soils as well as more neutral soils.

Unfortunately, there are few sources for obtaining Rhizobium cultures. I did find one source, Becker Underwood in Australia with worldwide production and marketing, for purchase of CB3060. The USDA has a Rhizobium Germplasm Collection that provides free cultures for research but they do not have a database of strains available. You can see a list of other bacterial culture collections worldwide.

For a good discussion of seed treatment and nitrogen fixation see Agroforestry for the Pacific Technologies from the U. S. Forest Service and also Nitrogen Fixing Tree Start-up Guide from Agroforestry.com.

You can also check with the Williamson County Extension Office of the Texas Agricultural Extension Service and see if they know of the availability of Rhizobium strains.