The study summarizes the information - experimental data and NLEAP (Nitrate Leaching and Economic Analysis Package) (Shaffer et al., 1991) model simulations, obtained from 1995 through 2005 on the regime of nitrate leaching of irrigated vegetable crops grown on Fluvisol in a typical horticultural region. The field trials have been conducted in the experimental station near the village of Tsalapitsa (24o35' E; 42o14' N; 180 m a.s.l.), southern Bulgaria and involved vegetables grown as: (1) single crop: potato (1995 year); carrot (2001 and 2004 year); pepper (1997, 1999 and 2002 year); aubergine (1998 and 2005 year); green bean (2000 year); and (2) compact crops rotation: potato-cabbage-lettuce (1995-1996 years); carrot-spinach-green pee (1996-1997 years), green bean-cabbage (2003 year). The nitrogen fertilizer rate in the so-called optimal treatment was calculated in accordance with crops' demands and varied between 80-180 kg.ha-1. The other two treatments were with 50 % below and 50 % above the optimal levels. During the first years of the experiment (1995-1998) two types of nitrogen fertilizers were tested – ammonium nitrate and urea, with two ways of application – one-time (spread before sowing) and split (before sowing and as a dressing). Nitrogen fertilizer was applied together with a background treatment with 80-100 kg.ha-1 phosphorous and potassium for each year from the experimental period. Chemical elements' migration through the soil profile was monitored by modified Ebermaier-Shilova type of lyzimeters cut into the soil at 1m depth from the soil surface. Nitrogen contents in all components of the plant-soil-groundwater system were monitored. The NLEAP model was parametrized by using experimental soil and vegetable crops data. The reliability of NLEAP model was tested in regards to the nitrate leached out of 1m soil layer and residual soil nitrogen in the experimental years. It was found acceptable coincidence between measured and simulated amounts and seasonal distribution of drainage water and leached nitrogen. The character of seasonal and year-to-year dynamics of nitrate leaching under different agrotechnical management was evaluated using the sequential runs with the event-by-event time scale of the NLEAP model. The climate conditions varied from extremely hot and dry for this region in 1995 and 2000 year, when the April-September precipitation was less than 161 mm (probability of exceedance 0.90) to extremely wet in 2001 and 2005 year, when this parameter was more than 415 mm (probability of exceedance 0.10). This resulted in significantly high variations in the leachate volumes.The highest quantities of drained water was observed during 2002 year in the cases when the irrigarion application was followed by a precipitation event and in extremely wet 2005 year. In most studied cases it was observed an enhanced migration of nitrate nitrogen at the highest N rates The nitrate content in the crop decreased when the nitrogen fertilzer was split applied. Fertilization with ammonium nitrate resulted in a considerable increasing of nitrogen content in the lyzimetric water compared to the variants treated with urea. The amount of the residual mineral nitrogen in the soil profile after the compact rotation was insignificant and was not the precondition for a groundwater nitrate contamination. Annual quantity of leached nitrate-nitrogen out of the 1 meter soil layer for the whole period depending on different N rates and vegetable crops ranged between 2.0 – 40,0 kg.ha-1. When the meteorological conditions in 2002 year destroyed the pepper production at the middle of the vegetation period one of the highest loss of nitrate-nitrogen (38.0 kg.ha-1) occurred under the highest fertilzer rate variant. The climatic conditions during the studied period were the most risky factor for the horticulture in the region and for groundwater nitrate contamination.