Effects of combined application of organic manure and chemical fertilizers on crop yields,Soil fertility and nutrient balance were studied systematically according to the results of a 13-year located experiment.The results show that the basic productivity of lou soil in Guanzong could be kept in a shorter period of time.The amounts of soil nutrients supplied for corn were higher than those for wheat.So,the application of N and P in combination with organic manure would be an efficient way for raising crop fields and soil fertility in irrigated area.