PHYSIOLOGICAL-STUDIES ON SALINITY AND NITROGEN INTERACTION IN ALFALFA .1. BIOMASS PRODUCTION AND ROOT DEVELOPMENT

The effects of the interaction between salinity, nitrogen (N) forms and concentration were studied with alfalfa (Medicago sativa L.) grown in pots with fine sand under greenhouse conditions. Increased salinity (0-100 mM NaCl) substantialy reduced the dry weight of roots and shoots, relative growth rate (RGR) of the plant, relative multiplication rate of root, mean extension rate of root, number of root branches, and root length. Additional N considerably moderated the salinity effects on these parameters. The promotive effect of nitrate-N was more pronounced on shoot and root dry weight and root lengths while number of root tips relatively increased more by ammonium-N on all salinity levels, Moreover, salinity affected root length per plant relatively more than number of root tips per plant. The plants were relatively tolerant at the second harvest to salinity and N levels. It is suggested that exogenous supply of N as nitrate would improve the vegetative growth of alfalfa by moderating the suppression by salinity effects. This was also observed that during vegetative growth, alfalfa plants do not require excessive N for further shoot regrowth. It was inferred that the extent of moderation of salinity effects depends on N forms, concentration and growth stages.