In order to have information and data on nitrogen balance of different types of farms in the region of Souss-Massa (Morocco), the apparent balance method was used in this study. The terms of the balance are expressed on per hectare basis of cropped agricultural land using the difference between the Sum of Inputs (kg N/ha/year) and the Sum of Outputs (kg N/ha/year). The balance of the different cropping systems showed a very highly significant difference between them. The average nitrogen surpluses (balances) are very disparate between farm types ranging from 23 kg N/ha/year in extensive cereal farming associated with vegetables and 1026 kg N/ha/year for the system characterized by diversified intensive vegetables (tomato, melon, green bean, pepper, cucumber) as well as the mixed system of banana and diversified intensive vegetables (tomato, watermelon, melon) having each one a high nitrogen surplus (about 1000 kg N/ha/year). The systems characterized by a monoculture of intensive tomato greenhouse production, citrus and diversified intensive vegetables, are similar and had an average surplus of 270 kg N/ha/year. The nitrogen balance is strongly correlated with inputs (r = 0.98 ***) and outputs (r = 0.94 ***). The results also showed that the use of nitrogen fertilizers and unsustained irrigation remains the main determining factor in aquifer nitrate pollution as nitrogen surplus is generally leached on sandy soils of low storage capacity.

Key words: Nitrogen balance, cropping systems, nitrogen fertilization and nitrate pollution.