Physiologycal evaluations of droght tolerance in sugar beet as a result of nitrogen and potassium fertilizer application.

Nitrogen and potassium are the most important elements in sugar beet nutrition. However, water stress causes nitrogen absorption to be reduced and over irrigation causes nitrogen is drained from root zone. The effects of water stress is reduced by closing stomata via increasing potassium concentration. So, finding balance between nitrogen and potassium level and diferrent irrigation regimes is very important. This study was done in karaj and mashhad. Physiological investigation of drought tolerance of sugar beet in relation to nitrogen and potassium absorption were conducted at (SBSI) kamal Abad and meshkin abad (Soil and Water Institute) field experiment and in mashhad in Torogh experimental station. The field experiments layout were designed in split plot where the main factor was three irrigation managements as fallow: W1= control or no water stress, irrigation was repeated when 50 percent of available water was depleted. W2=water stress after plant establishment, irrigation was resumed when 95 percent of available water was depleted after plant establishment and then irrigation was repeated when 50 percent of available water was depleted. W3=stress throughout growing season, irrigation was repeated when 95 percent of available water was depleted. In nitrogen or potassium experiments, the sub plot was three level of nitrogn or potassium concentration (n1or K1= percent lower recommended amount, n2 or K2= recommended amount, n3 or K3= 50 percent over recommended amount ) and sub-sub plot was two varieties (Bulk71127 and B.P. mashhad). Results showed that plant establishment were affected by drought stress. The most important reasons was soil crack at the middle of furrow specially in experiment that were carry out at clay soil in kamal-abad. So, in clay soil, it is recommended sugar beet seeds were drilled at the edge of farrow. Results also showed that in both experiments with increasing drought stress duration root and top yield reduce and re-irrigation could not cause root yield to be restored. Results in karaj showed that in ordinary (control treatment) there was no differences observed between two varieties but in drought condition root yield of B.P mashhad was significantly higher than root yield of Bulk 7112. In mashhad, root yield of Bulk 7112 was higher than root yield of BP mashhad. Regarding to root quality, with increasing drought stress duration, Pol slightly increased. But due to increasing α-amin and k and Na the molasses significantly increases and consequently juice purity reduced. Results in karaj also showed that leaf growth of Bulk 7112 in the mid growing season were higher than leaf growth of B.P mashhad variety but at harvest time the story reversed and top yield of B.P mashhad were higher than top yield of Bulk 7112. Results showed that there was positive correlation between soil nitrate or ammonium ion in 0-30 cm soil depth at the end of growing season and the amount of nitrogen concentration in root and molasses but negative correlation with sugar content and white sugar yield. Results also showed that there is positive correlation between amount of potassium in root and sugar content. Results showed that with increasing soil potassium concentrationin, plant could collect more potassium where, when the potassium concentration were just 200 mg/kg in soil the absorption was negligible but with increasing potassium concentration to 333 and 455 mg/kg the potassium absorption were 95 and 160 mg/kg. So, it can be concluded that when potassium concentration in a soil is less than 333 mg/kg, potassium fertilizer must be added to some how that the potassium deficiency is compensated. Keywords Water stress, growth, Karaj