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Viability of Rhizobium in Fertilizer Slurries Used for Hydroseeding¹

ABSTRACT

Drastically disturbed lands such as surface-mined areas often require fertilizer, lime, mulch, and seed for adequate revegetation. Hydroseeding is the most common seeding method used in mountainous, uneven terrain. Where legumes are included as part of the seed mixture, inoculation with Rhizobium is recommended, since disturbed areas are likely to be devoid of desirable indigenous rhizobia. Hydroseeder slurries are sometimes found to be acidic because of the fertilizer components added. The influence of fertilizers on pH, and resultant Rhizobium viability in slurries was examined in order to establish recommendations for hydroseeder mixtures. Of the fertilizer components commonly used for hydroseeding, only those with phosphorus (P) were found to influence slurry pH. Addition of triple superphosphate (TSP) resulted in a pH of 2.9, as compared with diammonium phosphate (DAP), which had a pH value of 7.7. Significant loss of Rhizobium viability occurred at pH values of < 6.0. Pulverized agricultural lime (CaCO₃) did not alter slurry pH; however, hydrated lime (Ca(OH)₂), when added in sufficient amounts, increased the pH to levels favorable to the survival of added rhizobia inoculant. Based on the results of this study, a hydroseeder slurry should contain enough DAP in the fertilizer blend to have a pH of 6.0 (at least 40% of P from DAP) in order to ensure rhizobial survival of sufficient duration to allow effective inoculation of the legume seed. Different Rhizobium strains can possibly vary in tolerance to acidity; however, acidity can be easily corrected to avoid any possible problem.

Key Words: minesoil • disturbed land • seeding inoculum • revegetation • reclamation • nitrogen fixation

¹ A contribution from the Departments of Agronomy, Horticulture, and Biology at Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-7294.

² Research Assistant, Associate Professors of Agronomy and Horticulture, and Assistant Professor of Microbiology, respectively.

Received for publication October 4, 1982.