The experiments presented here had in the objectives to compare different chemical fertilization and weed control methods, with the use of compost as fertilizer and a flex-tine harrow for mechanical weeding. In 1996, trials were established in a four years crop rotation: fallow→ barley (Hordeum vulgare L. ) → vetch (Vicia sativa L.) ground ploughed→ durum wheat (Triticum durum Desf.), in semi-arid regions. The results of 29 trials performed since 1999 to 2003 are presented here. In all of them three fertilization levels [organic (2500 kg compost/ha made by cereal straw and sheep manure), chemical (100-60-60) and no fertilized] and weed control levels [a flex-tine harrow tillage, a conventional herbicide application and untreated control] were studied in cereal plots with a bifactorial statistical model. Cereal production increased significantly only in the 21% and 17% of the chemical and organic fertilizer treatments respectively. Under these conditions the application of any fertilizer is not economically justified. The crop rotation had a very important preventive effect. Following the fallow and ploughed vetch periods, weed density was generally low in cereal plots (74 pl/m² average on untreated plots). Herbicide had the same average effectivity as mechanical control (about 50%). The smaller weed density obtained with any treatments only meant a significant higher grain production with respect of untreated plots in the 11% and 3.5% of the chemical and mechanical weed control treatments respectively. Mechanical control was observed negative for cereal production the 7% of the occasions. Consequently, both weed control methods are not considered efficient to increase the cereal yields in these conditions.