Abstract: Under conditioas of applying and without applying organic manure in the fields with cinnamon soil of medium-high fertility and with double cropping system, the efficiency of long-term application of N P K and their effect on soil nutrients were studied in Hebei province 10 year field experiments and 2 year pot tests showed that N fertilizer had a significant yield-increasing effect: Under normal weather conditions P and K fertilizers did not show obvious effect when caghnic manure was applied, but P would give a significant effect in the years when the weather was frigid in the winter and spring. After stopping applying organic manure, application of P fertilizer showed a significant effect on the winter wheat, and N P combination would be the best application form. In this experiment the effect of combined application of N P K fertilizers on organic matter in soil and nitrogen contents was small. P K contents in the soil changed with the variation in applied amount of P K. On the basis of organic manure, N 15kg/mu, P₂O₅ 8 kg/mu,K₂O 18kg/mu were applied on the soil every year, the NPK contents in soil showed surplus. Under conditions of applying the chemical fertilizers in aforementioned amount but without having organic manure, N P K in the soil were lacking.

Key words: Organic manure, N P K fertilizers, Fertilizer efficiency, Soil nutrient