Abstract: The effect of plastic film mulching,water storage in soil profile before sowing,and nitrogen fertilization on crop yield and nitrogen efficiency was examined in this paper.The study site was on the cultivated lossial soil in semiarid areas with 415mm of annual rainfall and the test crop was spring wheat,Triticum aestivum.In order to study the effect of plastic film mulching,4 levels of mulching were designed,including mulching of 0,30 and 60 days after sowing and mulching over the whole growing period.The results showed that increase of soil water storage,plastic film mulching and nitrogen fertilization increased crop yield significantly(α<0.01),and their effect followed in the order of nitrogen fertilization>increase of water storage>plastic film mulching.The effect of mulching on crop yield varied with water storage,nitrogen fertilization and mulching periods.When the water storage was low,there was no significant difference in crop yield between mulching and no mulching,although mulching increased crop yield slightly,and the nitrogen efficiency was higher for no mulching and mulching 30 days.When the water storage was high,the difference between the yield of muching 60 days and no mulching was significant,but no difference in nitrogen efficiency was found for mulching 30 days,60 days and over whole growing period.It was suggested that mulching over whole growing period was of less significance in practice.

Key words: Dryland, Plastic film mulching, Crop yield, Nitrogen efficiency, winter wheat, biotic factors., soil respiration, Weihe Plain, environmental factors