الفهرس 
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Abstract
This work was postulated to study the possibility of reducing the pollution hazard and NO3accumulation in lettuce vegetable plant. Therefore, the treatments were postulated to study the fertilization effects of different Nsources and levels, combined with organic manure fertilizer on lettuce content of free nitrate and its yield. This trial was conducted at the Agric. Exp. Station of ElMansoura Univ. during the second year of this investigation (2002001). This trial was designed mainly to asses the most suitable form (NO3 or NH4+), time and rate of nitrogen fertilizer application for lettuce plants and to follow up NO3 accumulation in the tested plants due to these treatments. These treatments were carried out with and without organic manure addition. The Nmineral fertilizers of this trial were either NH4NO3, (NH4)2SO4 or the combination between them with 4 levels i.e. 30,45, 60 and 90 kg N 1fed (0.24, 0.34, 0.48 and 0.72g N pot1) in addition to the control treatment. Each pot was fertilized with 0.2 cm3 from FYM which equal to 25 m3 fed1 in addition to the control. A splitsplit plot design with replicates was adopted. The main plots were Farmyard manure treatments (with and without FYM). The sub plots were occupied by the 3 mineral Nfertilizer treatments (NH4NO3, (NH4)2SO4 and NH4NO3+ (NH4)2SO4), while the subsub plots were Nfertilizer rates (zero, 30, 45, 60 and 90 kg N fed1). A field experiment was carried out at the farm of Agriculture Fac. ElMansoura Univ., during the winter season of 19992000 to evaluate the fertilization effects of different levels Nmineral sources separately or combined with the organic farmyard manure on NO3 accumulation, yield and the N, P and K uptake of lettuce vegetable plant (Lactuca sativa). The experiment treatments included five sources of nitrogen ammonium nitrate, ammonium sulfate, diammonium phosphate , Urea and Ammonia solution) with 2 levels, i.e. 60 and 90 kg N fed1 in addition to the control treatment. The FYM rates were 25 and 50 m3 fed1 in addition to the control treatment. Every treatment was replicated 3 times. N doses were divided into 2 equal quantities the 1st application was done after 21 days from transplanting of seedlings (3/1/2001) and the 2nd was at 15 days later (18/1/2001). A splitsplit plot design with 3 replicates was adopted. The main plots were farmyard manure (FYM0, FYM1 and FYM2). The sub plots were occupied by the five mineral Nfertilizers treatments (F1, F2, F3, F4 and F5), while the subsub plots were three Nfertilizer rates (Zero, 60 and 90 kg N fed1).