Field evaluation of lentil cultivars inoculated with Rhizobium leguminosarum bv. viciae strains for nitrogen fixation using nitrogen-15 isotope dilution

A N-15 isotope dilution technique was applied to quantify the extent of N-2 fixation in lentil (Lens culinavis Medik.) cultivars as influenced by Rhizobium leguminosarum by. viciae strains in a field experiment in Pakistan. The experiment was conducted on a soil with a very small indigenous rhizobial population and where N was a limiting factor for crop production. Significant variations in number of nodules, dry weight of nodules, biomass yield, grain yield, total N yield, proportion of plant N derived from Nz fixation (P-fix) and amount of N derived from the atmosphere (N-dfa) were observed among combined treatments of four rhizobial strains and six lentil varieties. In a field previously labelled with N-15, to which a basal dose of 75 kg P2O5 ha(-1) was applied as single super phosphate, N-dfa ranged from 15 to 24 kg N ha(-1) when calculated according to rhizobial strain and from 4 to 38 kg N ha(-1) when calculated according to lentil variety. Lc 26 was the most effective strain and fixed 243% more N than the indigenous population in the uninoculated control. In treatments with the lentil variety PL-406, N-dfa was 38 kg N ha(-1), which was 850% higher than with the lentil variety Precoz/F6-20-1xM-85. Generally, the varieties with greater P-fix produced a higher dry matter yield.