Study of Root Exudate Organic Acids and Microbial Populations in Palm Oil Seedling Rhizosphere

Mutual interaction between plants and microbes occured in the rhizosphere is expected to increase productivity of crops or soil fertility for agriculture. Plants secrete root exudates to attract microbes, and then microbes obtain habitat and food supply from plants and can fulfill the nutrient requirements through assisted enzymatic activity. The purposes of this study were to study 1) the types and amounts of root exudate organic acids, 2) microbial population, and 3) the relationship between root exudate organic acids and microbial populations in the rhizosphere of oil palm seedlings. The study was conducted in a greenhouse with planting medium using a sterile quartz sand by two factorials completely randomized design with three replications. Factor 1 was oil palm seedlings age (control / no oil palm seed, 1, 3, 6, 9 and 12 months-old) and factor 2 was the length of the growing season (45, 90, 135 and 180 days) with 72 experimental units. HPLC analysis revealed that four kinds of organic acids were found with the highest concentration were: acetic acid (1.66 ppm), citric acid (0.157 ppm), Malic acid (2.061 ppm) and oxalic acid (0.675) ppm. Soil microbials analyzed by the pour plate method with parameters of the total population of bacteria, fungi, Azotobacter, bacteria and phosphate solubilizing fungi were found with the consecutive highest amount: 19.38 x 106 cfu g-1 of soil, 3.28 x 104 cfu g-1 of soil, 12.09 x 105 cfu g-1 of soil, 8.39 x 104 cfu g-1 of soil and 1.15 x 104 cfu g-1 of soil. There is a positive correlation between root exudate organic acids with total microbes, fungi, Azotobacter, PSB and PSF