Variability in seedling growth and natural nodulation of different acacia species and seed sources of Acacia auriculiformis A. Cunn. Ex Benth and Acacia mangifera Willd.

Results of Experiment 1 on the variability in the natural growth and nodulation of different acacia species showed that growth of the five exotic acacia species were significantly affected independently by soil, species, different N levels of fertilizer and the combined interactions of these factors. Growth of the acacias were observed to be higher in Puting Lupa than in Luisiana soil. Application of N-fertilizer at different dosages enhanced the growth of Acacia seedlings and improved the utilization of available elements and nutrients for translocation in their tissues. Combined N on the other hand, depressed and suppressed nodulation of the seedlings as shown in lower nodulation number and nodule weight. All acacia species showed variations in their nutrient requirements and efficiency of utilization. Higher N was observed in seedlings growing in Puting Lupa soil while potassium, calcium and magnesium were higher in seedlings grown in Luisiana soil. Regression and correlation analysis showed that biomass yield is positively correlated with soil types, N level, shoot, root dry weight, height and diameter with r squared of 0.57. Results of Experiment 2 on the effect of seed sources on the growth of A. auriculiformis showed that faster and higher growth of the seedlings were observed in Philippine and Papua New Guinea which were superior than Thai and Australian provenances. Variation in nutrient content and uptake differs among the seed sources. Inoculation with Aa2 did not enhance nodulation and nodule weight of the seedlings by the different provenances. Highly positive correlation with diameter and height was obtained with r squared of 0.441, root dry weight, soil, shoot, diameter and height with r squared of 0.405; biomass, shoot, root, height and diameter with r squared of 0.92. Results of Experiment 3 on the provenance trial of A. mangium with Rhizobium inoculation in two soils showed that seed sources from the Philippines, Australia and Papua New Guinea performed better and exhibited faster rate of growth in all parameters assessed than the Sabah seed source