A long term field experiment designed to compare the effect of farm yard manure with mineral dressing on a mollisol was started at La Platina Experiment Station in 1963. A wheat-beans rotation fertilized with 0, 4, 8 and 16 ton, of farm-yard manure and the same amount of NPK applied as chilean nitrate, superphosphate and potassium sulfate has been sowed for 25 years. Wheat yields were always better when a mineral dressing was used. In the last 13 years the average yields of wheat were 27, 32 and 42 qqm/ha for treatments without fertilizers, 16 ton farm-yard manure and NPK mineral fertilizer equivalent to the nutrients input in the farm-yard manure, respectively. In beans there were no important differencies due to fertilization systems. During the last 13 years the highest level of organic matter (2.9%) is detected on the 16 ton manure plot and the lowest (2%) in the check plot. pH and available N do not show any change associated to the treatmenl. Available phosphorus and potassium, and electrical conductivity were changed. Farmyard manure greatly increased available P. The physical properties of the soil were improved with farmyard manure: porosíty and water holding capacity were increased.