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 under different nitrogen sources. Three salinity levels (0, 40 and 80 mM NaCl) and three NO3-/NH4+ ratios (6/0.5, 6/1 and 6/2) were applied in nutrient solutions. Under non saline conditions, the enhance of ammonium concentration increased turf quality (TQ), leaf NO3-, proline content , nitrate reductase activity (NRA), shoot and root growth. On the other hand, leaf potassium (K+) sodium (Na+) and malondealdehyde (MDA) content were not affected. During the first week the 40 mM NaCl treatment showed that the positive effects of NH4+ on salinity tolerance were still perceptible, However, the 80 mM NaCl treatment showed that the adverse effects of high salinities were more pronounced when turf fed with high ammonium rate nutrient solution, as manifested by the decrease of TQ, NO3-, NRA, K+/Na+ ratio, shoot and root growth and by the increase of leaf MDA content; this suggests that effects of NO3-/NH4+ ratio on salt tolerance varies with salinity levels.

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