Effect of Salinity Stress and Nitrogen Source on Nitrogen Remobilization in Two Alfalfa Cultivars

In order to study the effect of salinity stress and nitrogen forms on nitrogen remobilization from root to shoot following defoliation and shoot dry matter production, a research in the form of factorial experiment based on randomized block, was designed in three replications. Treatments include: 1) nitrogen forms containing a) biological N fixation (N1), b) 6mM NH4NO3(N2), c) biological N fixation+, 6mM NH4NO3(N3), 2) salinity in two levels containing 1/1 ds/m (S0) and 12 ds/m(S1) and 3) two Iranian alfalfa cultivars (Bami and Gharehyonjeh). Salinity stress decreased nitrogen availability in root and shoot, nitrogen remobilization and shoot dry matter. Percentage of this reduction in Ghareyonjeh cultivar was higher than Bami cultivar. According to positive correlation between nitrogen remobilization to shoot following defoliation and shoot dry matter production (r = 0.86), it was hypothesized that the effect of salinity on reduction of alfalfa shoot regrowth resulted from reduction in nitrogen remobilization. The highest nitrogen remobilization was related to N2 and N3 treatments although the percent of remobilization in N1 treatment was higher. Due to salinity, amount of nitrogen remobilization decreased in all nitrogen forms but percentage of this reduction was higher in N2 and N3 treatments. Percentage of increase in sodium content due to salinity in N2 and N3 treatments was higher than N1. According to appositive correlation between root sodium content and nitrogen remobilization (r = -0.83), it is possible that greater decrease in nitrogen remobilization and shoot dry matter production following defoliation in N2 and N3 treatments resulted from greater increase in sodium content in these treatments.