Production of biomass for energy, food or biomaterials requires certain agricultural practices. The increasing nitrogen loading due to inorganic fertilizers used in conventional agriculture is one of the major global environmental challenges. This research was conducted in central part of Croatia near Park of nature Lonjsko polje, on experimental field which was established 17 years ago in order to determine influence of mineral nitrogen fertilization on nitrate leaching. The soil type of trial site is drained distric Stagnosols and four different nitrogen fertilization levels are taken into consideration: 1. N0+P+K, 2. N100+P+K, 3. N200+P+K, 4. N300+P+K (kg N ha-1). Water samples were taken in periods with lysimeters discharge. Soil sampling (0-0.25 m) was carried out four times in the investigated period from June 2007 to June 2008 during the vegetation of maize and winter wheat. Research results indicate that the soil NO3-N content significantly varied (27.3 kg ha–1 to 338.2 kg ha –1) depending on the treatment and sampling time. Compare to the winter sampling time (November 2007 and February 2008) significantly higher content of soil NO3-N was determined in the summer sampling (June 2007 and June 2008). Regarding to the water samples, results revealed that the total nitrate-nitrogen losses were in the range from 5.97 kg NO3-N ha-1 to 112.3 kg NO3-N ha-1. Lysimeter discharge varied in dependence on precipitation and crop type. Total amounts of precipitation during the investigation were 652.5 mm and 34.6 % of them were recorded in lysimeters. Average NO3-N concentration in lysimeter water varied from 2.4 mg L-1 (0 kg N ha-1) up to 54.5 mg L-1 (300 kg N ha-1)
