Abstract

UTILIZATION OF 15N DILUTION ANALYSIS FOR MEASURING EFFICIENCY OF BIOLOGICAL NITROGEN FIXATION UNDER SOIL SALINITY STRESS

Suad A. Al-Saedi*, Ibrahim B. Razaq and Norrya A. Ali

ABSTRACT

The current work was conducted to evaluate the effect of salts content of soil on the efficiency of Biological nitrogen fixation by local rhizobium strains using the 15N dilution technique. Local strains obtained from Iraqi provinces, from Basra down south to Sulymania up the north, were isolated from cowpea rhizospher. They were purified, identified, Authenticated, characterized and propagated. Salt content, equivalent to 3, 6, and 9 dSm-1, effect on BNF%, nodules number, plant dry weight and total N content of cowpea were determined. Isolates showed different efficiency of BNF under different salinity levels. Generally, BNF of all isolates were the least at the highest level of soil salinity, which is 9.0 dSm-1. Local isolates respond differently to different soil salinity levels. The third level of soil salinity, which is equivalent to 112 mM, is the critical salinity level of BNF for all isolates. However, nodules number was significantly decrease with the
increase of soil salt content. Plant dry weight under all isolates decrease linearly with the increase of soil salinity.

Keywords: Rhizobium, local Iraqi strains, Cowpea, Total N, Nodules number, dry weight.