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In organic farming, crop fertilization is largely based on the decomposition of organic matter and biological fixation of nutrients. It is therefore necessary to develop studies conducted to know and understand the soil biological processes for the natural nutrient supplies. The effect of three fertilizer managements (chemical with synthetic fertilizers, organic with 2500 kg compost ha-1, and no fertilizer) in a rainfed crop rotation (durum wheat-fallow-barley-vetch as green manure) on different soil biochemical parameters in semi-arid conditions was investigated. Soil organic matter, microbial biomass carbon, organic matter mineralization, CO² production-to-ATP ratio, and NO3-N content were analysed. Fertilization was only applied to cereals. The results showed the scarce effect of the organic fertilization on soil quality, which resulted more dependent on weather conditions. Only soil organic matter and NO3-N were affected by fertilization (significantly higher in the inorganic treatment, 1.28 g 100 g-1 and 17.3 ppm, resp.). Soil organic matter was maintained throughout the study period by the inclusion of a legume in the cropping system and the burying of crop residues. In fallow, soil microbial biomass carbon increased considerably (816 ng g-1), and NO3-N at the end of this period was around 35 ppm, equivalent to 100 kg N ha-1. [ABSTRACT FROM AUTHOR]