A comparative study of organically and conventionally managed soils under beans was conducted to study the added advantage of organic crop production system over the conventional one. A comparative study of Rhizobium isolates, from the two management systems, for their potential beneficial activities was also carried out.The organically managed soils had better status with respect to physicochemical and microbiological properties and the Rhizobium isolate from the organic farm possessed significantly higher plant growth promoting potential as compared to those from the conventional farms. Organic farm of Sher-e-Kashmir University of Agricultural Science and Technology of Kashmir India was taken as a standard and rest of the samples were collected from various districts of the valley.The results revealed that the soil of the organic farm has significantly higher content of organic carbon (1.04%),available nitrogen, (298.7 kgha-1)phosphorus (16.72 kgha-1),potassium (296.30 kgha-1), dehydrogenase activity (68.7µg TPF/24 hr g-1 soil),total viable bacteria (78.90×106 cfu g-1 soil),fungi(48.73×103 cfu g-1 soil), actinomycete (27.20×103 cfu g-1 soil),phosphate solubilizing bacteria (18.30×105 cfu g-1 soil) and mycorrhizal spores (4.10 spores g-1soil) followed by that of district Kupwara rhizosphere soils with organic carbon (0.97%),available nitrogen (293.0 kg ha-1),phosphorus (15.81 kg ha-1),potassium (252.3 kg ha-1),dehydrogenase activity (62.7µg TPF/24 hr g-1 soil),total viable bacteria (72.60 ×106 cfu g-1 soil ),fungi (45.76×103 cfu g-1 soil), actinomycete (24.3 ×103 cfu g-1 soil),phosphate solubilizing bacteria (14.8×105 cfu g-1 soil) and mycorrhizal spores(3.8 spores g-1soil). Rhizobium bacteria were also isolated from the effective nodules of the bean plants grown at different places of various districts in kashmir valley,India.These isolates after identification were screened for the production of IAA,GA and siderophores.The isolate (Rhizobium phaseoli OF) from Organic farm was found most promising by producing 39.20 µl,162 µl, and 24µl of IAA,GA and siderophore respectively which was followed by 37.5 µl,153 µl,and 21µl of IAA,GA and siderophore respectively from the isolate obtained from rhizosphere soils of Kupwara district. The isolate (Rhizobium phaseoli OF) was used in combination with three levels of fertilizer nitrogen(0,20 and 40 kg ha-1 ) in a field experiment with beans as experimental crop and five replications by adopting RBD design to study the impact on various plant growth and yield attributing features such as number of pods per plant, pod weight and number of nodules. Nitrogen uptake,apparent nitrogen recovery and percent soil nitrogen utilization was also estimated.Maximum number of pods (12 plant-1) was recorded under the treatments T5 andT6.Significantly maximum pod weight (5.96 g) and number of nodules (60.45 plant-1) was observed under the treatment T5.Treatments T5 and T6 were at par with respect to nitrogen uptake in grains (63 and 64 kg ha -1),plant biomass (84 kg ha-1) and total N uptake (147 and 148 kg ha-1 ) by plant. Maximum apparent nitrogen recovery (210) and percent soil nitrogen utilization (46.37) was recorded from the treatment T5.From the present study it was concluded that the organic management is better option for sustaining the soil health and further the potential Rhizobium isolate may be mass multiplied and used on a large scale for harnessing its plant growth promoting potential.
Key words: Rhizobium, plant growth promoting activities, nitrogen fertilizer, soil health