M. Arghavani - Department of Horticulture, Faculty of Agriculture, University of Zanjan, Zanjan, P. O. BOX: ۳۱۳-۴۵۱۹۵, Islamic Republic of Iran.
A. Zaeimzadeh - Department of Horticulture, Faculty of Agriculture, University of Zanjan, Zanjan, P. O. BOX: ۳۱۳-۴۵۱۹۵, Islamic Republic of Iran.
S. Savadkoohi - Department of Horticulture, Faculty of Agriculture, University of Zanjan, Zanjan, P. O. BOX: ۳۱۳-۴۵۱۹۵, Islamic Republic of Iran.
L. Samiei - Department of Ornamental Plants, Research Center for Plant Sciences, Ferdowsi University of Mashhad, Mashhad, Islamic Republic of Iran.

In most semiarid and arid areas, fresh water shortage compels managers to use low quality water sources with high salinity to irrigate turf and landscape. Recent research has noticed that management of nitrogen fertilization can alleviate salinity effects on plants. This greenhouse sand culture experiment was conducted in order to investigate morphological and physiological responses to salinity stress in Kentucky bluegrass (Poa pratensis L.) grown using different nitrogen sources. Three salinity levels (۰, ۴۰ and ۸۰ mM NaCl) and three NO۳-/NH۴+ ratios (۶/۰.۵, ۶/۱ and ۶/۲) were applied in nutrient solutions. Under non saline conditions, higher ammonium concentration increased Turf Quality (TQ), leaf NO۳-, proline content, Nitrate Reductase Activity (NRA), shoot and root growth. On the other hand, leaf potassium (K+) sodium (Na+) and MalonDiAldehyde (MDA) content were not affected. During the first week, the ۴۰ mM NaCl treatment showed that the positive effects of NH۴+ on salinity tolerance were still perceptible. However, the ۸۰ mM NaCl treatment showed that the adverse effects of high salinities were more pronounced when turf received high ammonium rate nutrient solution, as manifested by the decrease of TQ, NO۳-, NRA, K+/Na+ ratio, shoot and root growth and by the increase of leaf MDA content. This suggests that effects of NO۳-/NH۴+ ratio on salt tolerance varies with salinity levels.

Morphological and physiological responses, NO۳-/NH۴+ ratio, Salt tolerance