Influence of various combinations of diazotrophs and chemical N fertilizer on plant growth and N2 fixation capacity of oil palm seedlings (Elaeis guineensis Jacq.)

The Biological Nitrogen Fixation (BNF) process, which involves diazotrophic microorganisms, is an important agricultural practice for improving crop yield and environmental quality. Although diazotrophs have a positive interaction with the host plants and can reduce the need for N fertilizer, BNF alone cannot meet the N requirement for maximizing host plant yield. Thus, a combination of plant N2 fixation and the response to small amounts of nitrogen starter should be considered. The study was conducted to observe the effects of diazotrophs on growth of oil palm seedlings and to determine influence of four strains of diazotrophs and different concentrations of nitrogen source on oil palm seedlings. The tested diazotrophs were Herbaspirillum seropedicae (Z78) and the locally isolated Microbacterium sp. (E7 and E14) and Acetobacter sp. (E9). The host plants were inoculated with the diazotroph strains, and also fertilized with different N fertilizer concentrations (0, 25, 50 and 100%). The seedlings were harvested after 360 days of growth and measured for plant dry weight, root density, nutrient accumulation and total leaf chlorophyll and protein content. Acetylene Reduction Assay (ARA) was performed to quantify nitrogenase activity of the diazotrophic microorganisms. The results successfully showed that strains Z78, E7 and E14 could potentially enhance growth of oil palm seedlings if supplied together with low levels of N fertilizer.