Two field experiments were carried out during winter seasons of 2000-2001
and 2001-2002 to estimate the optimum N level for growth. yield and quality
parameters of potato plants grown on sandy soils under drip irrigation system and arid
conditions of central region of Saudi Arabia. Five N levels of 0, 100, 200. 300 and 400
Kg N ha" were tested. The results Indicated thai the fresh and dry matter yields of shoots and
tubers as well as the total carbohydrate yield in tuber dry matter significantly
Increased in form of a quadratic equaUon curve with increasing of N fertilization rales.
The highest fresh and dry maller yields of shOots and tubers as well as the tctal
carbohydrate yield in tuber dry matter were obtalned as calculated average N
application rate of aboul255 Kg N ha' using the second ploynomial equations in both
seasons. While the optimum economic level of N fertilizalion for growth . yield and
lotal carbohydrate yield was observed at 100 and 200 Kg N ha" (as average. 150 Kg
N ha") at the two seasons. Shoot and tuber content of N was signlficafltly increased.
while P and K content insignfficanlty increased with N application rales. On the other
hand. Shoot and tuber N. P and K uptake by potato plants was significantly increased
with increasing N fertilization levels. Soil salinity (ECe) was insignificantly increased with increasing N fertlli2atlon
rate. while soil pH was slightly decreased. Available soil N was significantly increa8ed
with Increasing N application rate. However. increasing N fertilization rate has slight
effect on the available soil P and K.