A pOI experiment was performed at Soils Department, Faculty Of Agriculture
Mansoura University during 2001 growing season 10 determine Ihe effect of water
salinity levels (0.4. 1.0, 2.0 and 3.0 dSm'\ SAR levels (3.5, 7.0 and 14.0) and the
simplest combination between the levels 01 the previous factors on elemental
distribution. nutrients uptake and the productivity of onion plant. The obtained results can be summarized in: Under the experiment conditions, the correlation studies between irrigation
waler studied characters and bulbs fresh weight reveal that the reduction rate in bulbs
fresh yield by increasing water salinity by one unite is dependent on SAR value and
the adverse trend is true . At SAR of 14.0 ,Increasing water salinity by 1 dSm"
decreased the yield o( bulbs fresh weight by 24.940 % . While at SAR of 3.5 the
reduction rate under the same increase in water salinity was 19.550 %. At EC
value of 0.4 dsrn" ,raising SAR value one urute decreased the bulbs rresh weight by
2.071 % ,while at EC value of 3.0 dSm" Ihe reduction amounted to be 4 240 %. The obvious trend was also obtained as a result of the effect of water salinity
and SAR on the dry weights of bulbs. cutis and roots. RaiSing irrigation water salinity and {or waler SAR increased cults dry weight
{bulbs dry weight ratio . Whenever, this ratio at the treatment of 0.4 dSm" and SAR of
3.5 was increased from 31.13 % to 62.02 % at the treatment of 3.0 dSm".and SAR
of 14 . RaiSing irrigation water salinity increased N, p, K and Na contents in onion
ptant parts RaiSing SAR of irrigation water increased Na content up to the highest
level of SAR (14). While phosphorous content was increased up to SAR levels of 7.0
then decreased after that. RaiSing irrigation water salinity and I or SAR decreased KINa ralio. The relative nitrogen USe efficiency was reduced from 100% to 56.96 as a
result of water salinity increasing from 0.4 to 3 d sm", while raising SAR from 3.5 to 14
decreased the relative nitrogen use effiCiency from 100% to 54.03%. Phosphorus uptake by onion plant in this study amounted to be from 12.48 to
19.95% of thaI N upta'Ke. Increasing irrigation water salinity and lor water 5AR reduced N.P and K
uptake, So. alterecl the distribution pattern of each. While, sodium uptake was
increased with increasing waler SAR, bul decreased by increasing waler sallmty,
and the amount of sodium uptake by plant is very small compared to that of N, P and
K, these renect the highest onion ion uptake selectivity.