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Abstract Ahmed El Sayed Fahmy Mohamed: Optimizing of Nitrogen Fertilization under Drip Irrigation System in Sandy Soil Using Nuclear Techniques. Unpublished Ph.D. Dissertation, Department of Agricultural Engineering, Faculty of Agriculture, Ain Shams University, 2016. Sand soil is characterized as poor fertile and no structured one therefore irrigation water may lose rapidly from the soil profile. Cultivation of such soils needs more attention to be paid for water and nutrient, especially nitrogen, management. In this regard, nitrogen management should provide an adequate supply for a crop throughout the growing season. If the amount of nitrogen is limiting at any time, there is a potential for loss in production. This work aimed to improve nitrogen efficiency as affected by irrigation water regime, N forms and rates (splitted doses). Therefore, a field experiment on sandy soil was conducted to trace the beneficial effects of urea and ammonium sulfate fertilizers added at different rates on pea growth and nutritional values as interacted with different water regimes. 15Nisotope dilution technique was followed to distinguish between the different N proportions derived to pea plants and in the same time estimating the efficient use of both two nitrogen forms (%NUE). Water regime and fertilization treatments were applied under surface drip irrigation system. Two water regimes represented 100% and 75% of water requirement in combination with three N fertilizer rates, i.e. N0, N100 and N75 were applied. The overall means of seed yield as affected by nitrogen fertilization treatments represent relative increase accounted for 45.8%, 38.7%, 41.7% and 36.2% over the unfertilized control for Urea100, Urea75, Ammonium Sulfate100 and Ammonium Sulfate75, respectively. It seems that 100% water regime (W1) made nitrogen fertilizer, especially with high rate, more available for plant uptake comparing to the low water quantity regime. Pea crop had accumulated more nitrogen from urea comparing to ammonium sulfate fertilizer. Nitrogen uptake, in general, significantly correlated to application rate.W1water regime in combination with ammonium sulfate fertilizer resulted in the best percentage or absolute values of N derived from fertilizer by pea seeds. It was clear that efficient use of ammonium sulfate, to some extent, doesn’t affected by different water regimes. This holds true either at 100% or 75% application rates. On the other hand, urea added at rate of 75% was more efficiently used by seeds than those added at rate of 100% of the recommended rate. Application of 75% of Etc (W2) treatment gave a remarkable yield and pronounced water saving therefore it is technically and economically recommended. For instant, the overall mean of water regime indicated that seed yield (2184.4 kg ha-1) achieved by W1 (100%) was nearly closed to those obtained with W2 (75%) (2167.4 kg ha-1). Key words: 15 N, Irrigation Regimes, Nitrogen Fertilizer Form, Pea and Water use efficiency. ACKNOWLED. |