Grazing sheep on alfalfa in the fall is widely accepted in the southern half of California, but is viewed with skepticism for a number of reasons in the northern part of the state. The greatest concern expressed by northern California growers is the possibility of increased soil compaction and subsequent reduction of water infiltration and yield. The potential for entry of pathogens into injured alfalfa crowns is also of concern. A lesser but still important concern is the possible introduction of weed seeds contained in fecal droppings or caught in the wool. We therefore began a three-year research program in the fall of 1984 at the University of California, Davis, to study the effects of fall grazing sheep on alfalfa.