INFLUENCE OF BACTERIAL INOCULATION ON MAIZE IN UPLAND FARMING SYSTEMSOF THE SIKKIM HIMALAYA

A field experiment using three strains of Azotobacter chroococcum and two of Azospirillum brasilense was carried out at two elevations in Ma mlay Watershed, Sikkim, India. A local maize variety was used as the t est crop. The treatments (applied by seed inoculation) resulted in sta tistically significant improved plant performance at the subtropical l ocation where yield enhancement of 1.15-fold over control was recorded with one of the bacteria. Azotobacter chroococcum W5 (originally a wh eat isolate) gave the best performance. Observations recorded for vari ous microbial communities indicated stimulation of some of the native, beneficial groups of microorganisms. During the middle of growing per iod there was a 2-5-fold increase in the population of actinomycetes, and a group of bacteria able to grow on N-free medium. This suggests t hat the observed effects of seed inoculation on plant growth may in pa rt be due to the stimulation of already existing plant growth-promotin g rhizobacteria in and around roots. Bacterial inoculation also result ed in significantly higher values for nitrogen and phosphorus content of plant components. Seed inoculation did not result in improvement of plant performance at the temperate location. This was probably due to the inability of the introduced bacteria to establish or survive at l ower temperatures. (C) 1998 Elsevier Science Ltd. All rights reserved.