Response of Acacia auriculiformis to Rhizobium inoculation and ash application at varying N-levels

Rhizobium inoculation with either of the two strains (Aa2 and Aa3) proved to be effective for Acacia auriculiformis seedlings. Height, shoot biomass, root biomass, and nodule oven-dry weight of the seedlings were markedly enhanced by inoculation. An appreciable increase in P, Ca, and Mg contents and in N, P, K, Ca, and Mg uptakes were also noted. Likewise, N fertilization greatly influenced the growth and nodulation of the seedlings. Generally, significantly taller and heavier plants were obtained at 30-300 kg/ha N application, however, nodule development was reduced at higher levels of nitrogen (300 kg N/ha). Nitrogen fertilization at 300 kg N/ha also resulted in higher N-content but the concentration of other macronutrients were generally improved by the application of N at lower doses. Higher uptakes were also observed with N-fertilization (30-300 kg/ha) as compared to the unfertilized seedlings. On the other hand, A. auriculiformis responded negatively to ash application. All the growth and nodulation variables as well as the macronutrient uptake were consistently and significantly higher in the seedlings which were not treated with ash application. The interaction between inoculation and N-fertilization gave no significant results in all of the parameters except for macronutrient content wherein N was found to increase with N-fertilization alone at 100-300 kg/ha application, but this did not differ significantly with those which were inoculated alone with either Aa2 or Aa3. The concentrations of other macronutrients in the shoot were generally increased by inoculation with modest amount of fertilization. Likewise, the combined application of ash and inoculation remarkably improved the N, P, and Mg-contents of the plant than either inoculation or ash application alone. An appreciable increase in P and Mg concentrations were also observed with the combined application of ash and N-fertilizer while the three-factor interactions gave favorable results only in terms of P, Ca and Mg contents with P-content being markedly improved by inoculation at 300 kg N/ha with ash application.