INOCULANT, PHOSPHORUS AND NITROGEN RESPONSES OF LENTIL

Abstract

Three field experiments were conducted in 1987 to determine the effect of inoculant, phosphorus and nitrogen on yield and N2 fixation by lentil (Lens culinaris Medik.). Sites were located in the Brown, Dark Brown and Black soil zones of Saskatchewan. The experiments were laid out in a split-split-plot design: main plot treatments were no inoculant, commercially available Nitragin ’C’ inoculant and inoculant containing a superior Rhizobium strain, 99A1; subplot treatments were 0 and 30 kg P2O5 ha−1; sub-subplot treatments were 0, 10, 20 or 25, 40 or 50, and 90 kg Nha−1. N2-fixation was estimated by 15N-isotope dilution using barley (Hordeum vulgare L.) or uninoculated lentil as the non-N2-fixing reference crop. At all sites, lentil inoculated with 99A1 had the highest yields and N2 fixed while uninoculated lentil had the lowest. Phosphorus responses only occurred at the site in the Black soil zone which had the most favorable growing conditions and lowest available soil P levels. Phosphorus application increased dry matter and grain yields but did not affect N2 fixation at this site, indicating that the legume host was more responsive to P application than the rhizobia. Total dry matter was always increased by application of N, with the greatest response in the uninoculated treatment. Grain yields were significantly increased by N fertilization at all sites for uninoculated lentil, one site for ’C’-inoculated lentil, and no sites for 99A1-inoculated lentil. Significant yield increases of ’C’-inoculated lentil due to N application indicates that ’C’-rhizobial strains were incapable of supplying sufficient N for maximum yields at these sites. Inoculated lentil receiving 0 to 10 kg N ha−1 obtained 58–75% of their N from the atmosphere; higher N rates reduced this percentage significantly due to substitution of fixed N with fertilizer N. The amount of N2 fixed in the grain ranged from 4 kg ha−1 under drought stressed conditions in the Brown soil zone to 57 kg ha−1 in the Black soil zone.Key words: Lens culinaris, nitrogen, phosphorus, Rhizobium leguminosarum, yield, nitrogen fixation