Assessment of growth and nodulation of Acacia mangium Willd. and Sesbania grandiflora (L.) Pers. in two Philippine soil types

Liming and inoculation and/or fertilizer amendments significantly affected the growth parameters of Acacia mangium and Sesbania grandiflora considering the three factors, the former species exhibited consistently best height, diameter, shoot and root biomass, nodule dry weight, nutrient content and uptake on Adtuyon clay loam soil. Sesbania grandiflora grew better and produced more nodules in Annan clay soil. Liming the soil did not improve the growth and nodule development of A. mangium but it did in S. grandiflora. Seedlings of both species grown in both soil fertilized with 200 kg N and 100 kg PK per hectare has the best growth followed by those that were fertilized by PK and inoculated with Rhizobium. Height, diameter, and nodule dry weight of the two species were significantly affected by the interaction of the three factors. Highly significant independent interaction effects of soil, inoculation and nitrogen in some of the parameters of the two species were observed. Significantly taller plants were obtained at 200-400 kg N/ha in both soil types but nodule development of S. grandiflora was reduced at higher levels of nitrogen (300-400 kg/ha). The combined effects of the three factors influenced expressively the height, diameter and shoot and root biomass of A. mangium and the nodule number only of S. grandiflora. Correlation and regression analyses revealed highly significant relationship between shoot biomass and nodule number, nodule dry weight and nitrogen uptake. Local Rhizobium isolate (Am2) can replace about 91% of the nitrogen requirement of A. mangium in Adtuyon clay loam while the introduced strain (TAL 78) from Hawaii can substitute about 91% also of the N-requirement of S. grandiflora in the same soil type. The obviously better effect of soil types on growth and nodulation of the two species was attributed to the inherent physio-chemical properties of the soil, introduction of a more effective and competitive rhizobia than native soil population in the presence of a modest booster of inorganic nitrogen.