A pot experiment was performed at Soils Department. Faculty Of Agriculture
Mansoura University during 2002 growing season, to study the effect of nitrogen
fertilization {0.606,O.909 and 1.212 g nitrogen pol" , irrigation water salinity levels
(0.4, 1.0,2.0 and 3.0 d'Srn") , water sodium adsorption ratio values (3.5, 7.0 and 14.0)
and their interaction on nutrients uptake and yield of onion plant. The obtained results showed that.: Under the experimental conditions, the relative bulbs fresh weight was decreased by
62.76% whenever the irrigation water salinity was increased from 0.4 dsrn' (control)
to 3.0 dSm" . Also, raising the irrigation water SAR value from 3.5 to 14.0
decreased the bulbs fresh weight by 31.19 %. The bulbs fresh weight was increased
as nitrogen fertilization dose Increased at any level of irrigation water salinity and / or
irrigation water SAR value, and the positive effect of 19m nitrogen addition pol" is
equal to the negative effect of raising irrigation water salinity by 1.412 dSm" or raising
SAR of the irrigation water by 13.851 . The bulbs fresh weight return was increased as a result of increasing the
nitrogen applied dose, from N1 to N3 with increasing the irrigation water SAR up to
the highest level was used under the lowest level of irrigation water salinity ,while,
under the highest one, the adverse trend was obtained with the same raising of both
N fertilization and irrigation water SAR . Raising the nitrogen fertilization dose, reduced the culls dry weight / bulbs +culls dry
weights ratio in contrary to the effect of the higher irrigation water salinity and lor
irrigation water SAR. Within the studied range, increasing the nitrogen applied dose led to improve
the nitrogen distribution pattern among the plant parts against to the effect of higher
salinity and / or sodicity of irrigation water. The relative phosphorus use efficiency, was increased by 50.48 % with
increasing the nitrogen applied dose, from N 1 to N3 at the first level each, irrigation
water salinity and irrigation water SAR. Increasing the irrigation water salinity
increased from 0.4 to 2.0 dSm'\ , beside increasing the N applied dose from N1 to N 3
the relative phosphorus use efficiency was increased by 1 5.797% . Raising t he
irrigation water SAR from 3.5 to 14.0 beside the previous increase in both N
fertilization . and irrigation water salinity reduced the relative phosphorus use
efficiency by 22.417 % The highest irrigation water salinity and lor irrigation water SAR decreased
the potassium uptake by bulbs more than in other parts, and nitrogen increased the
potassium uptake by bulbs more than in other parts. The multi linear regression equations revealed that ,raising the irrigation
water SAR by unity caused a negative effect approximately equal to that of 1/10 dsm'
, with respect of fresh or dry matter production. and equal to that of 2110 dSm" with
respect of total nitrogen, phosphorus and potassium uptake. Hence raising irrigation
water SAR within the studied range affected nutrients uptake rather than fresh or dry
matter production.