Artículo en prensa en Proceedings of the 4th World Congress on Conservation Agriculture CONSTRAINTS TO ZERO TILLAGE IN MEDITERRANEAN ENVIRONMENTS. E. Acevedo * , E. Martínez and P.Silva Laboratorio de Relación Suelo-Agua-Planta. Facultad de Ciencias Agronómicas. Universidad de Chile. Casilla 1004. Santiago. Chile. Abstract The projected world food demand will require a sustainable intensification of field crops agriculture, fine tuning genotypes and agronomy for the various growing environments. No-till is central to agricultural sustainability, yet its adoption in Mediterranean environments is lagging behind, particularly in high yielding areas. These environments are characterized by having winter rainfall and hot, dry summers such that crop residue decomposition on top of the soil does not start until the break of autumn rains and decomposition occurs at low temperatures. The accumulated residues cause problems to the planters; allelochemicals limit germination and cause seedling mortality and sexual reproduction of pathogens occurs on the residue during the summer. When rainfall is high slugs thrive in the cool, humid environment provided by the straw. Eventually farmers burn the residues defeating a major purpose of conservation agriculture. Based on our experience with no-till in Central Chile, a high yielding Mediterranean environment, we briefly analyze the effects of crop residues on the soil, the effect of crop residues on the next crop of the rotation and propose agricultural practices and ideotypic traits of wheat for no-till that would help to overcome most of the production problems in these environments. The proposed traits are intended to overcome changes that occur in soil mechanical impedance, anoxia, weed control, diseases and allelopathy when no-till practices are adopted. Key words: No-till, cereal crops, sustainable agriculture. INTRODUCTION Globally the wheat demand is expected to increase to one billion Mg by the year 2020, what implies a fantastic intensification of the production systems to almost double the mean wheat yield, from 2.5 to 4 Mg ha -1 (Rajaram, 2001). The intensification has to be done in a sustainable way and it will require an almost perfect coupling of genotypes, * Corresponding author: Tel.-fax: +56 2 9785858; E-mail address: eacevedo@uchile.cl.