15N-Determined Effect Of Inoculation With N2 Fixing Bacteria On Nitrogen Assimilation In Western Canadian Wheats
Published 1987 ·
SummaryA two-year field study was undertaken using15N isotope techniques to differentiate between stimulation of N uptake and N2 fixation in Western Canadian cultivars of spring wheat (Triticum aestivum L. emend Thell) and durum (T. turgidum L. emend Bowden) in response to inoculation with N2-fixing bacteria.Bacterial inoculation either had no effect or lowered the % N derived from the fertilizer and the fertilizer use efficiency. Despite the depression of fertilizer uptake, inoculants did not alter the relative uptake from soil and fertilizer-N pools indicating that bacterial inoculation did not alter rooting patterns. Nitrogen-15 isotope dilution indicated that N2 fixation did occur.In 1984, % plant N derived from the atmosphere (% Ndfa) due to inoculation with Bacillus C-11-25 averaged 23.9% while that withAzospirillum brasilense ATCC 29729 (Cd) averaged 15.5%. In 1985, higher soil N levels reduced these values by approximately one-half. Cultivar x inoculant interactions, while significant, were not consistent across years. However, these interactions did not affect cultivars ‘Cadet’ and ‘Rescue’. In agreement with previous results, ‘Cadet’ performed well with all inoculants in both years while ‘Rescue’ performed poorly.Among 1984 treatments, the N increament in inoculated plants was positively correlated with % Ndfa but no such correlation existed in 1985. N2 fixation averaged over all cultivars and strains was 17.9 and 6.7 kg N fixed ha−1 in 1984 and 1985, respectively. Highest rates of N2 fixation were estimated at 52.4 kg N ha−1 for ‘Cadet’ in 1984 and 31.3 kg N ha−1 for ‘Owens’ in 1985, both inoculated with Bacillus C-11-25, an isolate from southern Alberta soils. Inoculation with either ofAzospirillum brasilense strain Cd (ATCC29729) or 245 did not result in as consistent or as high N2 fixation, suggesting that these wheats had not evolved genetic compatability with this exogenous microorganism. These agronomically significant amounts of N2 fixation occurred under optimally controlled experimental conditions in the field. It is yet to be determined if N2 fixation would occur in response to bacterial inoculation under dryland conditions commonly occurring in Western Canada.