Inoculation of nitrogen fixing bacteria in conjugation with integrated nitrogen sources induced changes in phenology, growth, nitrogen assimilation and productivity of wheat crop

Numerous strains of plant growth-promoting bacteria are used as biofertilizers to minimize the utilization of synthetic fertilizers, improve nutrients use efficiency, crop productivity and to reduce environmental pollution. This study was planned with the aims to assess the effects of seeds inoculation with different strains of nitrogen (N)-fixing bacteria in conjugation with N fertilization from various combinations of farmyard manure (FYM) and urea on days to anthesis, days to physiological maturity, leaf area duration (LAD), crop growth rate (CGR), net assimilation rate (NAR), physiological N use efficiency (PNUE), apparent N re-translocation (ANR), relative N accumulation rate (RN), N harvest index (NHI) and grain yield of wheat crop under the environmental conditions of Northern Pakistan. The experiment was carried out in RCB design with a factorial arrangement of treatments. Wheat seeds were inoculated with N-fixing bacterial strains viz. Azotobacter sp., Azospirillum ER-20, Rhizobium SK-8 and Pseudomonas K-1, and N were applied from three different combinations of FYM and urea i.e. 100% urea, 75% FYM and 25% urea, and 50% FYM and 50% urea. The results showed that days to anthesis (122), days to physiological maturity (162), CGR (10.31 g. m−1. day−1), grain yield (4016 kg ha−1), PNUE (43.1 kg grain kg−1N uptake), ANR (9.1 g kg−1 DM), NHI (79.4) and RN (0.1046 day−1) were increased (P < 0.05) by Azospirillum Er-20 and Pseudomonas K-1 inoculation, while maximum (P < 0.05) LAD (76 m. day−1) and NAR (0.19 g. m−1. day−1) were attained on Rhizobium SK-8 inoculation with N from 50% FYM and 50% urea, as compared to control. The grain yield revealed a significant (P < 0.001) correlation with CGR (0.76), NHI (0.72) and PNUE (0.68). The regression analysis exhibited a good estimate for grain yield (R2 = 0.83) and CGR (R2 = 0.57) in response to soil mineral N content. In conclusion, bacterial inoculation in conjugation with an equal ratio of N from the integrated sources improved the phenological and growth traits as well as N assimilation and grain yield of wheat crop. Therefore, it is suggested to plan long-term experiments to explore the potential of N-fixing bacteria in conjugation with integrated N-sources under different agronomic conditions for attaining sustainability in the wheat cropping systems.