Site condition - As there were appreciable variations within the same plantation area in either growth or soil or slope or all in some localities, due care was taken to identify the appropriate location. Collection of soil samples - Soil samples at 0-6cm depths were collected with spade. To represent the site, several soil samples were collected from a particular depth in a sample plot. Then soils of a particular slope of a site were mixed in equal proportion to have a composite sample. The samples were taken in polythene bags and brought into laboratory. Each soil sample was divided into two sub-samples, one for the determination of physical and chemical properties and the other was used for the estimation of nitrogen-transforming microorganisms including Azotobacter, ammonifying bacteria, Nitrosomonas, Nitrobacter and denitrifying bacteria. Laboratory analysis - Soil samples were air dried and passed through a 2mm sieve. Soil samples were kept in refrigerator for prior to microbial study. Soil pH was determined in 1:2 soils (air dry): 0.01M CaCl2 suspensions with an electronic digital pH meter. Particle size analysis was done according to Bouyoucos Hydrometer method and the textural class names were those of USDA. Soil organic carbon was determined by Walkley and Black’s wet oxidation method. Cation exchange capacity was determined by 1N NH4OAC saturation followed by 10% KCl displacement. Exchangeable Na+, K+ were extracted with 1N NH4OAC solutions (pH 7.0). Available phosphorus was extracted from field moist soil samples by Bray and Kurtz No. 1 extractant (0.03N NH4F in 0.025N HCl) and determined according to the SnCl2 reduced molybdophosphoric blue colour method. Potassium and sodium were determined by flame photometer. Soil sample dilution - Ten gram of each soil sample was suspended in 95 ml sterile distilled water in a conical flask, and mixed well with the help of a stirrer to get 10-1 dilution of the soil sample. Ten ml of this suspension was transferred to another conical flask containing 90 ml sterile distilled water and mixed well with the help of a magnetic stirrer to get 10-2 dilution. In this way by gradual transfer and mixing 10-3, 10-4, 10-5, 10-6, 10-7 dilutions were prepared. Estimation of Azotobacter - Five tubes containing 10 ml sterile solution (Mineral salt solution: K2HPO4-5g, MgSO4.7H2O-2g, CaSO4-1g, FeSO4-0.2g, MnSO4 - 0.2g, MoO3. H2O- 0.1g, KI-0.1g, Distilled water-1000 ml. 10 g sucrose, 3g CaCO3 and 900 ml of distilled water was added to 100 ml of the mineral salt solution) were inoculated with 1 ml of particular dilution. In this way the dilutions from 10-1 to 10-3 were used for the inoculation of tubes of solution. The inoculated tubes were incubated at 28ºC for 1 week. Development of skin or pellicle on the surface of the culture fluid showed the positive result. Most Probable Number (MPN) of Azotobacter was calculated with the help of MPN chart from the number of positive tubes inoculated with higher dilutions. Estimation of ammonifying bacteria - Five tubes containing 7 ml sterile nutrient broth solution (Peptone-5g, Beef extract-3g, NaCl- 1g, Distilled water-1000 ml) were inoculated with 1 ml of particular dilution. In this way the dilutions from 10-4 to 10-7 were used for the inoculation of tubes of nutrient broth. The inoculated tubes were incubated at 300C for 30 days. After incubation, 3 to 5 drops of Nessler’s reagent (Solution-A: Potassium iodide-70g, Mercuric iodide-100g, Distilled water-500ml. Solution-B: Sodium hydroxide-100g, Distilled water-500ml. Solution B was added into solution A in a 1000 ml volumetric flask. Then it was shaken well and distilled water was added to make 1000 ml) was added to each tube. Development of brown colour showed the positive result. Most Probable Number of ammonifying bacteria was calculated with the help of MPN chart from the number of positive tubes inoculated with higher dilutions. Estimation of Nitrosomonas The population of Nitrosomonas was determined using ammoniumcalcium carbonate medium {(NH4)2SO4-0.5g, K2HPO4 -1.0g, FeSO4.7H2O-0.03g, NaCl-0.3g, MgSO4.7H2O-0.3g, CaCO3 -7.5g, Distilled water - 1000ml}. Tubes of medium were inoculated with 1 ml of each of soil dilutions from 10-3 to10-7. Five tubes containing 3 ml medium were inoculated with each dilution. The inoculated tubes were incubated at 280C for 3 weeks. A set was included as uninoculated controls. After incubation, 3 to 5 drops of Griess-Ilosvay reagent was added to each tube. The presence of Nitrosomonas was indicated if the solution in inoculated tubes showed purplish-red colour. To all tubes that showed negative result, a small pinch of the Zn-Cu-MnO2 (1:1:1) mixture was added. Development of reddish colour showed the positive result for the presence of Nitrosomonas. Most Probable Number of Nitrosomonas was calculated with the help of MPN chart from the number of positive tubes inoculated with higher dilutions . Estimation of Nitrobacter - The population of Nitrobacter was determined by nitrite-calcium carbonate medium (KNO2 -0.006g, K2HPO4 -1.0g, FeSO4.7H2O - 0.03g, NaCl- 0.3g, MgSO4.7H2O-0.1g, CaCO3 -1.0g, CaCl2 -0.3g, Distilled water – 1000 ml). Tubes of the medium were inoculated with 1ml of each of soil dilutions from 10-3 to 10-7. Five tubes containing 3 ml medium were inoculated with each dilution. The inoculated tubes were incubated at 280C for 3 weeks. After incubation, 3 drops of Griess-Ilosvay reagent was added to each tube. The presence of Nitrobacter was indicated if the solution in inoculated tubes remained colourless. Most Probable Number of Nitrobacter was calculated with the help of MPN chart from the number of positive tubes inoculated with higher dilutions. Estimation of denitrifying bacteria - Each of 5 tubes containing 10 ml liquid medium (Solution-A: KNO3 -1.0g, Asparagine-1.0g, Bromothymol blue (1% in ethanol)-5.0 ml, Distilled water-500 ml. Solution-B: Na-Citrate-8.5g, KH2PO4 -1.0g, MgSO4.7H2O -1.0g, CaCl2.6H2O -0.2g, FeCl3.6H2O- 0.05g, Distilled water-500 ml. After preparation of solution A and B, they were mixed and pH of the medium was adjusted within the range of 7.0 to 7.2) for denitrification test was inoculated with 1 ml of each of soil dilutions from 10-3 to 10-7. The inoculated tubes were incubated at 300C for 7 days. Vigorous gassing and blue colouration showed the positive result. Most Probable Number of denitrifying bacteria was calculated with the help of MPN chat from the number of positive tubes inoculated with higher dilutions.