Effects of plastic film mulching and nitrogen fertilization on spring wheat growth progress and dry matter accumulation

A field experiment was carried out on cultivated loessial soil in semiarid area with 415 mm precipitation and spring wheat ( Triticum aestivum ) used as an indicating crop to study the effects of plastic film mulching period(including no mulching,mulching for 30 days,mulching for 60 days,after sowing and mulching for whole growing period),nitrogen fertilizer application (including no nitrogen application and nitrogen application 75 kg/hm 2 ) and soil water storage amount in soil profile before sowing (including low and high water storage amount)on the spring wheat growth progress and dry matter accumulation.The results showed that plastic film mulching could make the seedling 1-9 days earlier than no film mulching treatment (mostly 3-6 days earlier).Uncover film mulching in a eligible time can improve wheat growth process remarkably and benefit to last maturity stage.Earlier seedling had a significantly positive effect on the whole spring wheat growth process,it increased valid number of tillering and post filling for grain;the delayed maturity was beneficial for formation of big grain and increasing weight per 1000 kernel.Film mulching in all growing period might change wheat growth process but it also did harm to post growing period and decrease the kernel filling period,1000 kernel weight;increase invalid number of tilling.Film mulching at the earlier growing period could not only increase shoot matter accumulation remarkably but also had a vigorous effect on further dry matter accumulation and formation of yield in mid growing and post growing stages.The shoot biomass yield in the three film mulching treatments was the biggest at 60 days after sowing when the soil water storage amount was higher,and after this period,the shoot biomass yield appeared to decrease tendency.The shoot biomass yield was the biggest at 90 days after sowing of non mulching treatments in both low and high soil water storage amount before sowing,it showed that it remained maintain a high producing ability from 60 to 90 days for non-mulching treatments.As for unit area dry matter accumulation at 90 days after sowing,in high soil water storage amount condition before sowing,the biomass yield was the biggest in the treatment of mulching for 60 days,and in low soil water storage amount condition,the biomass yield was the biggest in the treatment of mulching for 30 days,it showed that high soil water storage water before sowing could delay mulching process in some extent.On the other hand,the two soil water storage amount treatments indicated simultaneously that difference among unit area dry matter accumulation in various treatments decreased as wheat growth process progress,it revealed that it did bad for photosynthate accumulation if film mulching continued in later wheat growing stage.View at the distribution of the biomass yield underground,the weight of the biomass yield,especially that of stem increased remarkably after mulching,resulted in decreasing of R/S as the wheat growth process progress.Obviously it hampered photosynthate flowing to the root after mulching,compared with non mulching treatment,R/S was the highest in earlier growing period,decreased remarkably in later growing period,it was the lowest at 90 days after sowing and stabilized after that.Generalized the result in two years,film mulching in earlier growing period of spring wheat was beneficial to maintain a high R/S ratio in later growing period;film mulching in whole growth period was detrimental to maintain a high R/S ratio.On the other hand,the negative effect of film mulching in whole growth period was to make much photoynthate flowing to stems and leaves,and reduce the harvest index.