Effect Of Straw Returning Combined With Nitrogen Fertilizer On Nitrogen Use Efficiency And Yield Of Maize

In 2017,China’s maize planting area was 42.399 million hectares,and the yield reached259.071 million tons.According to the grass-grain ratio of 1.2,the amount of maize straw reached31.085 million tons,and the straw resources were excessive.The smashing of maize straw directly returned to the field is an effective measure to reduce the straw burning and increase soil fertilizer.It is also an effective measure to realize its ecological benefits.The maize straw C/N is high,and the fertilizer nitrogen should be added after the straw is returned to the field to ensure the supply of nitrogen.The application of straw has a certain influence on the distribution of nitrogen.The experiment was carried out in the south-central part of the Songnen Plain.The frame experiment method was used to set up two main treatments: straw returning and straw removed,and setting three amounts of urea application,respectively are 0 kg·hm-2,175 kg·hm-2,350 kg·hm-2(The nitrogen conten of Urea t is 46%),and each fertilizer application amount set two methods of application,respectively are applied as base fertilizer and top dressing ratio is 1:1,another was applied as base fertilizer and top dressing ratio is 1:0.The top dressing measure was carried out after the sampling of the jointing stage.The fertilizer nitrogen applied was 15N-labeled urea(15N abundance is 3.60%).The experiment set ten treatments in total to study the effect of straw returning combined with fertilizer nitrogen on nitrogen use efficiency and yield of maize.The results showed that:From the seedling stage to the maturity stage,the change of soil available nitrogen content treated with straw showed as a single-peak curve.The soil available nitrogen content reach the highest value in the jointing stage.The soil available nitrogen content of the straw removed treatments gradually decreased.From the seedling stage to the maturity stage,the nitrogen content of the stalks decreased continuously.The nitrogen content of the grain in the maturity stage was higher than that of the stalks.The dry matter weight and nitrogen accumulation increased continuously.The straw returning treatments reduced the soil available nitrogen content in the seedling stage and jointing stage and reached a significant difference in the seedling stage.While it was higher than the straw removed treatments in the maturity stage.The straw returning treatments reduced the nitrogen content,dry matter weight and nitrogen accumulation of the maize in theseedling stage and jointing stage,while increased in the maturity stage.The proportion of fertilizer nitrogen account for the nitrogen uptake by maize of straw returning treatments was higher than that of straw removed treatments,and it is opposite after the jointing stage.Straw returning causes crops to absorb more soil nitrogenUnder the same nitrogen application rate,compared with the treatments of fertilizing in two times,dry matter weight,nitrogen content of grain at the maturity stage of the maize and the soil available nitrogen content in the maturity stage were lower than the one-time fertilization treatment.With the increase of nitrogen application rate,soil available nitrogen content,soil available nitrogen residue,fertilizer nitrogen ratio account for nitrogen absorbed and utilized by plant,dry matter weight and nitrogen accumulation increased.Under the conditions of this experiment,returning 12 t·hm-2 maize straw to the soil reduced the nitrogen use efficiency of maize.Under the same nitrogen application amount,the nitrogen use efficiency of topdressing treatments were remarkably higher than that of one-time fertilization treatments.Nitrogen use efficiency remarkably decreased with increasing nitrogen application rate.The nitrogen use efficiency under straw returning treatment were 25.27%~38.04%,and the fertilize rnitrogen use efficiency under straw removed treatments were 32.33%~40.05%.Under the same nitrogen application treatments,straw returning treatments increased yield of maize,but the effect was not significant.With the increase of nitrogen application rate,the yield remarkably increased.Under the same nitrogen application rate,the yield of topdressing treatments were lower than that of one-time fertilization treatments.