The pedoclimatic conditions in the West-African semiarid region frequently limit the growth of annual crops. Soil physical properties, in particular, limit crop root development. Ongoing studies conducted by Tropical Agronomic Research Institute (IRAT) researchers in Senegal and in other countries of the region have suggested that soil tillage favorably modifies these physical properties and especially the porosity of surface horizons. Such an increase in porosity immediately results in improved development of the root system and thus, in better shoot growth. For the farmer this can mean a significant increase in yield. After defining the soil and climatic conditions of the semiarid region of Senegal, the main results achieved from soil tillage practices on annual crop production and the relevance of these results to the establishment of trees will be summarized.