INFLUENCE OF VESICULAR-ARBUSCULAR MYCORRHIZAL FUNGI ON ALFALFA GROWN IN ARIZONA.

Abstract

In the glasshouse, two cultivars of alfalfa growing in non-sterile soil were evaluated for their response to inoculation with 4 VA mycorrhizal fungi and 3 strains of Rhizobium meliloti. Alfalfa cultivar Hayden PX-1 had significantly greater dry stem weights (p = 0.05) when inoculated with Glomus fasciculatum, G. deserticola or an undescribed Glomus sp. compared to mycorrhizal controls. Alfalfa cultivar Lew HI Nod had significantly less dry stem weights when inoculated with G. fasciculatum, G. mosseae or the undescribed Glomus sp. Addition to R. meliloti did not impart increased growth responses with either alfalfa cultivar probably due to the high nitrogen content of the soil. In the field, alfalfa cultivar Hayden PX-1 was both transplanted and direct-seeded. Transplanted alfalfa had been preinoculated with VA mycorrhizal fungi and R. meliloti. Inocula containing VA mycorrhizal fungi and R.meliloti were Layered below the seed in direct-seeded plots. Phosphorus, as treble super phosphate, was also added as a treatment. At first harvest, transplanted alfalfa inoculated with the undescribed Glomus sp. had significantly greater (p = 0.05) dry whole plot weights compared to controls regardless of R. meliloti or phosphorus treatments. Inoculation of alfalfa with G. deserticola significantly increased dry whole plot weights over controls but significantly (p = 0.05) only with added R. meliloti and phosphorus. Second harvest data maintained the trend for yield increases over controls with addition of the undescribed Glomus sp. and G. deserticola; however, only significantly (p = 0.05) with inoculation with the undescribed Glomus sp. including R. meliloti and phosphorus. Yield increases were not obtained for the final three transplanted alfalfa harvests or for any of the direct-seeded alfalfa harvests. Statistically significant differences in phosphorus and protein content of alfalfa were not found between any of the treatments. Also, differences were not found in soil populations of R. meliloti in mycorrhizal inoculated plots compared to control plots.