THE EFFECT OF WATER STRESS ON NITROGEN STATUS AS WELL AS WATER USE EFFICIENCY OF POTATO CROP UNDER DRIP IRRIGATION SYSTEM

Water and nitrogen management, rate and timing of application are critical factors in optimizing potato tuber yield and quality. This study was conducted to determine the effect of water stress and nitrogen fertilizer levels on canopy water content (CWC), soil water content (SWC), nitrogen uptake, SPAD values, water use efficiency (WUE) and potato yield. Water treatments concluded fully irrigated and water stress. While, nitrogen levels were (N0, N50 and N100). Surface drip irrigation system was used to provide irrigation water requirements. Treatments were irrigated when 35 % of available soil moisture was consumed in soil profile depth. For nitrogen levels (N0, N50 and N100) at water stress conditions, the percentage of irrigation water saved was 11.47 % led to decrease the tuber yield with 31 %, 13.94 % and 25.25 %, respectively. SPAD values were highest in water stress and lowest in the control. In addition, SPAD values were in a positive linear relationships with water and nitrogen treatments as a coefficient of determination with very high (R^2= 0.99 and 0.99), respectively. Also, increasing the nitrogen dose led to the increase the nitrogen uptake values. Moreover, nitrogen uptake presented a linear relationships with water regimes at nitrogen levels (0.96 and 0.97), respectively. Also, SPAD values presented linear relationships with nitrogen uptake at well water controlled, stressed and nitrogen levels (R^2= 0.99 and 0.99). In conclusions, there were obvious effects of water stress on CWC, SWC, nitrogen uptake and WUE. On the other hand, canopy water content and soil water content could be used to predict potato WUE and yield.