Nitrogen Fixation and Plant Growth Enhancement by Beneficial Rhizobacteria in Association with Oil Palm Seedlings

Abstract

Nitrogen fertilizer is the most expensive nutrient input in oil palm production with average total estimated cost amounting to RM 470 million yea(l. Rapid losses of N fertilizer through leaching further increases the cost on palm oil production and. makes the sector less profitable. Recently there is a new finding about an associated N2 fixing rhizobacteria which could be applied to the oil palm seedling production sector. The beneficial rhizobacteria has been reported to be efficient in N2 fixation and stimulates plant growth, thus could be used as a biofertilizer and bioenhancer, respectively, for various leguminous and non-leguminous crops. Therefore, a series of experiments were carried out to estimate the N2 fixing capacity of the rhizobacteria and to observe the effects of inoculation on growth and development of the associated oil palm seedlings. Results from the initial experiment indicated that Azospirillum could contribute 40% of the total N requirement of oil palm plantlets through N2 fixation process, stimulated total dry matter accumulation and root growth, stimulated uptake and higher concentration of N and K and increased the host photosynthetic rates compared to the control, after 120 days of planting (D120). The subsequent pot experiment (glasshouse experiment, harvested after 130, 260 and 390 days of planting (D130, D260 and D390)) demonstrated the potential of Azospirillum brasilense Sp 7 and locally isolated Bacillus sphaericus UPMB 1 0 and Bacillus subtilis UPMB 13 as a biofertilizer for oil palm seedlings through N2 fixation (25-50% Ndfa􀂇 Nitrogen derived from atmosphere) and stimulated higher concentration of essential nutrients and their accumulation especially N, P and K. The inocula also enhanced the development of roots (root dry weight, volume, primary root numbers and high R/S ratio) and tops (total dry matter, top dry weight, chlorophyll content, leaf area, plant height and stem diameter) of the host plants. Generally, effects of the inoculation at two monthly intervals were more promising during the earlier growth stage (D130-D260) with similar or better response compared to the control with complete Ni fertilization (Sp 7 k +Ni) especially for all root growth observations, top dry weight and total dry matter of the host plants. However, this improvement in plant growth was less than the control with complete Ni fertilization after an intentionally prolonged nursery phase, D390. A duplicated experiment as above was carried out in the field nursery station, FELDA Bukit Mendi, Pahang. The inoculation process showed positive response in enhancing higher concentration and accumulation of N, P and K for the host plants especially at D130, enhanced root growth (root dry weight, volume, primary root number, and R/S ratio) until end of the growth stages (D390) and top growth which includes total dry matter, top dry weight and chlorophyll content of the host plants (until D260).