This experiment was carried out during the two successive summer seasons of 2009 and 2010 at a Private Farm in EL-Salhaia El-Gadida region, Sharkia Governorate on potato plant (Solanum tuberosum L.) cultivar Diamantgrown under sandy soil conditions using drip irrigation system to study the effect of quantity of irrigation water (750, 1250 and 1750 m3/ fed.) and farmyard manure (10, 20 and 30 m3/ fed.) as well as their interactions on growth, yield and its quality as well as water use efficiency. Plant height, number of leaves/ plant, shoot dry weight, free and total water in leaf tissues, N, P and K percentages and their uptake by shoot significantly increased with increasing irrigation water quantity up to the highest level (1750 m3/ fed). Irrigation water quantity of 1250 or 1750 m3/ fed. recorded the maximum values of average tuber weight, tuber yield/ plant and total yield/ fed, N, P, carbohydrates, starch and DM percentages in tuber tissues. Bound water, cell sap, osmotic pressure and proline amino acid in leaf tissues as well as water use efficiency (WUE) by potato plants were significantly increased with decreasing irrigation water quantity up to the lowest level (750 m3/ fed). Farmyard manure (FYM) at 20 m3/ fed. significantly increased plant height, number of leaves/ plant, shoot dry weight, free and total water percentages, P % and its uptake by shoot, N, P, total carbohydrates, starch and dry matter % in tubers, on the other hand, N and K contents and their uptake by shoot, average tuber weight, yield/ plant and total yield/ fed. as well as water use efficiency were significantly increased with increasing FYM up to 30 m3/ feddan. Interaction treatment between water quantity at 1250 m3/ fed. and FYM at 30 m3/ fed. was the superior treatment for enhancing shoot dry weight/ plant, N % and its uptake by shoot, N, K and total carbohydrates in tubers. While, the interaction treatment between 1750 m3/ fed. water quantity and 30 m3/ fed. FYM gave the highest values of P and K percentages and their uptake by shoot, tuber yield/ plant and total yield/ feddan.