An organic fertilizer was applied to durum wheat (Triticum durum Desf.) and barley (Hordeum vulgare L.) crops in a rotation with vetch (Vicia sativa L.) and fallow in a semiarid dryland. The organic, chemical and no fertilizer effects on the long-term evolution of O.M., P and K, nitrate loss and crop nitrogen total content were compared during different periods. The high level of O.M. and P were maintained after 6 years of experiments even in the unfertilized plots while K slightly decreased. Thus, the rotation and straw and stubble burying were enough to maintain the initial nutrient contents. During the crop period, chemical fertilization significantly increased the nitrate content in the first 30 cm of soil, compared with organic fertilizer or no fertilization. However, the estimated nitrogen losses during the test period were similar in the three levels of fertilization, as well as the nitrogen extraction for the total biomass produced. Finally the crop yield was not increased after applying chemical or organic fertilizer, since the unfertilized plots production was similar.