Effects of plastic film mulching models and nitrogen fertilizer on wheat yield and nitrogen efficiency

Field experiments have been carried out on loess plateau in middle part with 415 mm average precipitation and in south part with 632 mm precipitation per year.In these experiments,spring wheat ( Triticum aestivum ) and winter wheat ( Triticum aestivum ) have been used as indicating crops to study the effects of plastic film mulching (for spring wheat,including non mulching,mulching for 30 days and 60 days after sowing,and mulching for the whole growing period;and for winter wheat,including non mulching,mulching for 75 days and for 150 days after sowing,and mulching for the whole growth period) and nitrogen fertilizer application (for spring wheat,including no nitrogen application and nitrogen application 75 kg N/hm 2,and for winter wheat,including no nitrogen application and nitrogen application 225 kg/hm 2 ) on wheat yield and N efficiency.The results showed that the effects of plastic film mulching on the yield and N efficiency differed according to the soil water storage amount before sowing,the application of N fertilizer,the course of plastic film mulching and rainfall in the growth periods.In 1999 with rich rainfall,no matter whether nitrogen fertilizer was applied or not,under the condition of low soil water storage before sowing,although the grain,straw and biomass yield under all the film mulching treatments increased,there was no significant difference compared with non mulching treatment (control);under the condition of high soil water storage before sowing,both grain and dry matter had the highest yield after film mulching for 60 days,and non film mulching had the lowest one.But,there was no significant difference between the non mulching treatment and film mulching for 30 days,and between film mulching for 60 days and film mulching for the whole growth period.In 2000 with the extreme drought,film mulching affected significantly the biomass yield.Under the conditions of low soil water storage before sowing and no application of nitrogen fertilizer,biomass yield increased markedly in the treatment of film mulching for 30 days,then was the treatment of film mulching for 60 days,and the last was the treatment of film mulching for the whole growth period.After applying nitrogen fertilize,the biomass yields difference between the non film mulching and the film mulching for 30 days,and between film mulching for 60 days and film mulching for the whole growth period did not reach significant level.In dealing with the plot of high soil water storage before sowing,if nitrogen fertilizer was not applied,there was not any difference,no matter how plastic film was mulched.The grain yield ranged from 1 430 kg/hm 2 to 1 482 kg/hm 2.When nitrogen fertilizer applied,the grain yield in the treatment of film mulching for the whole growth period was the highest,and there was no significant difference between the film mulching for 30 days and for 60 days.According to the average of two rates of nitrogen fertilizer application,there was no significant difference among various film mulching treatments.Because there werent notable difference of crop nitrogen content between different mulching treatments,the effect of film mulching treatment on crop uptake of nitrogen was the same as the effect on crop yield.But,it was obvious that film mulching during the earlier growth stage (e.g.film mulching for 30 days after sowing) could improve the nitrogen to transfer from straws to spikes (mainly in grain) in later growth stage.According to the analysis of the factors affecting the yield in two years experiments,the effects of film mulching on the number of spiklet and the valid number of spiklet were mainly factors affecting the grain yield.At the same time,the effects of film mulching course on the nitrogen fertilizer efficiency were related to precipitation in crop growth stage.In the year with rich rainfall,under low soil water storage before sowing,nitrogen fertilizer efficiency was the highest in the treatments of non film mulching and film mulching for 30 days,they were 30.4% and 30.3% respectively,while nitrog