Does lentil (Lens culinaris) in the Swat river valley need Rhizobial inoculation?

Rhizobium inoculation can increase yield and N2 fixation in lentil. This hypothesis was tested in a field experiment in the rainfed area of Swat River Valley using three inocula (Rhizobium leguminosarum), obtained from Australia, Tarnab and NARC Islamabad. Data were collected on various yield and N2 fixing, parameters, and total N, NH4-N, N03 -N, organic C, and moisture content of the soil were determined at harvest stage. The inocula from Australia and NARC significantly increased the number and biomass of nodules compared to the control treatment whereas the Tarnab inoculum did not exert any significant influence. The plant biomass was not affected significantly by any of the inoculation treatments. The grain yield was, however, increased significantly by inoculation but differences among the inoculated treatments were not significant. The N concentration and delta 5N in both lentil and reference plants were not affected significantly by inoculation. The N concentration ranged from 1.60 to 1.79% in lentil and from 0.9 to 1.4% reference weed plants. Similarly, the delta 5N ranged from -1. 39 to 1.20% in lentil and from 0.52 to 2.00% in reference weed plants. Similarly, neither the total crop N nor the N2 fixed in lentil was affected significantly by inoculation. Values for total crop N ranged from 38 to 47 kg ha- 1 and that of N2 fixed from 37 to 45 kg ha-1. The % Pfix was, however, increased significantly by inoculation. Values for Pfix were 85% in the control and 93 to 97% in the inoculated treatments. The total N in soil at harvest was not influenced significantly by the inoculation. Values for organic C were greater in the Australian than in other treatments. The moisture contents were almost the same for all treatments. It was observed that total mineral N increased from 25 kg ha-1 at sowing to 32 kg ha-1 at harvest stage which indicated that lentil contributed about 7.0 kg N ha- 1 to soil for the subsequent crop. These results indicated that the indigenous rhizobia were capable of fixing about 85% of crop N from the atmosphere. The inoculation, however, further enhanced this efficiency to 97%. Thus, it could be concluded that rhizobial inoculation of lentil in the Swat River Valley is useful but not necessary.