IRRIGATION MANAGEMENT OF DRIP-IRRIGATED POTATO PLANT GROWN IN SANDY SOIL Abdel-Nasser, G. Soil  and Agricultural Chemistry Dept. ,Faculty of Agriculture  Alexandria University ABSTRACT This study was carried out to investigate the effects of water regime under drip irrigation system on growth, tubers yield, tuber quality, leaf total chlorophyll, free proline and mineral composition as well as water relations of potato crop. The study was conducted at Ali Moubarek Village, EL-Boustan (North Tahrir Agricultural Experimental Station, 95 Km south of Alexandria-Egypt) during 2001/2002 growing season of potato crop. The texture of the experimental soil was sandy. Imported potato tuber seeds (Solanum tuberosum, L.) of Diamont cultivar were used in the present study. Planting was done on 2^ed of October 2001, in wet soil. The potato tuber seeds were planted at 0.25 m apart, in rows of 0.75 m width and 40.0 m length. Irrigation water was applied throughout a drip irrigation network using drippers of 4.0 L/hr capacity. The irrigation water was applied at six frequencies: 60, 70, 80, 90, 100 and 110% of reference evapotranspiration. The results revealed that foliage characteristics (i.e., plant height, shoot  fresh weight, shoot dry weight, shoot dry matter and shoot water content) were significantly affected by irrigation regime, in which increasing the amount of Irrigation water increased the vegetative growth. The data also, clearly indicated that increasing irrigation significantly increased leaf characteristics (total chlorophyll, leaf water contents i.e., free water content ( FWC), bound water content (BWC), total water content (TWC),  and  relative water content (RWC)). Leaf proline content substantially increased with increasing water stress (decreasing the amount of irrigation water). Increasing the amount of irrigation water resulted in increasing the leaf nutrients content. Irrigation at 90% of ET₀ resulted in improving the potato tuber physical and chemical characteristics. The maximum tubers yield was attained at 90% of ET₀ treatment (21.359 ton/fed.). In addition, the maximum water use efficiency was attained at the same level of irrigation water (17.249 kg tubers/ m³ of applied water). The most soil moisture was extracted from the top 40 cm soil layer and was found to increased significantly with increasing the amount of irrigation water. The optimum soil moisture tension for potato crop was between 0.25 and 0.35 bar. The most important outcomes from the present study are clarifying the important role of irrigation regime with drip irrigation system in improving the potato growth and tuber yield. Also, good distribution of moisture overall the root zone depth, that can enhance the plant growth and yield of potato crop. The present study recommends 90% of ET₀ (1238.3 m³ of applied water/fed) to achieve highest potato yield and tuber quality under the same present conditions.