Present high yielding cultivars available to farmers in Chile are not seriously affected by insects, pests or deseases that might be limiting grain production. Nitrogen fertilization and weed control practices are the two principal rice production constraints in the country. In this study, the effect of both agronomic practices on grain yleld of the three principal cultivars, during two crop season at several locations, is analyzed. Results obtained indicate that the economic yield potential is 6.6ton/ha,which is only possible to obtain when both nitrogen fertilization and weed control are complementarily used. Appreciable yield reductions are produced when either of them is omitted.