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. 1. Introduction Conventional farming has been important for improving food to meet human demands but has been largely dependent on intensive inputs of synthetic fertilizers and pesticides [1, 2], both from an economic and energetic point of view. In recent years, the relationship between agriculture and the environment has changed, and concerns regarding the sustainability of agricultural production systems have come to the fore [3]. In this context, organic or ecological farming, focused on the environment and public health, is increasing worldwide [4]. Organic farming avoids the application of synthetic biocides and fertilizers [5, 6], promotes the use of renewable resources to prevent pollution [7], may reduce some negative effects attributed to conventional farming, and may have potential benefits in enhancing soil quality [2]. Thus, plant production in organic farming mainly depends on nutrient release as a function of the mineralization processes in soils. Therefore, to get an active soil microflora and an important amount of available nutrients is crucial in these productive systems, being the goal “fertilizing the soil rather than the plant” a priority among organic farmers to assure sufficient nutrient mineralization
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