The Reserach On The Utilization Of Soil Nitrate By Crops In The North China Plain Under Water, Nitrogen Managements

In grain production,farmers applied a lot of nitrogen fertilizer into soil,and thenitrogen use efficiency was low.The result was that large amount of nitrate accumulated insoil,which posed a great threat to the groundwater environment.According to the aboveproblems,this paper took the most common grain crops of winter wheat and summer maizein the north of China as the research object,investigated the uptake of labeled nitrate-N indifferent soil layers by winter wheat at different growth stages,and the influence ofdifferent water and nitrogen managements on the root distribution of winter wheat andsummer maize,N uptake and the residual of soil nitrate by using the soil columnexperiment combined with field experiment. Aiming to determine the recovery of thenitrate accumulated in subsoil in wheat growth stages,improve water and nitrogen useefficiency,reduce nitrate leaching,which could provide a scientific basis and technicalsupport for the utilization of soil nitrate. The main results are as follows.（1） Most roots of winter wheat were concentrated in the0-40cm layer, and thedensity of roots decreased exponentially with increasing depth. The total root length anddry weight reached the maximum value at booting stage and the value under the treatmentN400was higher than that under N200at the jointing stage and booting stage. Moreover,the value of total root length under TM was the highest at mature stage. Most roots ofsummer maize were concentrated in the0-20cm layer, and the density of root length anddry weight decreased with increasing depth, the amount of nitrogen application andirrigation had little effect on the root distribution of summer maize.（2） The yield of winter wheat could significantly increase when the annual nitrogenapplication amount was400kg/hm²,and the irrigation had no significant effect on it,but3times spring irrigation>2times spring irrigation> no irrigation, The yield of the treatmentN400TD was6161.77kg/hm²,was the highest, which had the significant difference fromN200T0.The amount of nitrogen application and irrigation both had no significant effect onthe yield of summer maize,in all treatments N200TM had the highest yield,9700.04kg/hm².The total yield had no significant difference between treatments,but could find that inwinter wheat season2times irrigation, summer maize season1time irrigation couldimprove the total yield.The amount of nitrogen application and irrigation also had nosignificant effect on the nitrogen uptake by winter wheat and summer maize and thenitrogen distribution.The irrigation could improve the nitrogen use efficiency in winterwheat significantly, but had no significant effect on summer maize.It also found that increasing the amount of nitrogen application would decrease the nitrogen use efficiency inthe high-yield farmland.（3）In winter wheat season,increasing the amount of irrigation could significantlyincrease soil water content,especially above140cm soil layer.While in summer maizeseason only2times irrigation could significantly increase water content above60cm soillayer,and for the water content below120cm soil layer, the amount of nitrogenapplication was the main influence factor,that N200treatment was greater than N400treatment.It increased residual nitrate amount significantly to increase the amount ofnitrogen application,while increasing the amount of irrigation would promote the leachingof nitrate, the depth of nitrate accumulation peak was deeper in summer maize season thanin winter wheat season.（4）The biomass of winter wheat,N uptake,¹⁵N uptake and the¹⁵N use efficiencyincreased gradually with the prolongation of growth stages,and decreased with theincreasing depth of labeled-N in the soil proifle at any same stage.The accumulation peaksof nitrate and¹⁵N were around the labeled depth,the migration range of nitrate was70cm.（5）The biomass of winter wheat,N uptake and the nitrogen use efficiency of60cm,120cm irrigation and fertilization treatments were significant higher than180cmirrigation and fertilization treatment. Shallow irrigation promoted deep layer nitrate uptakeby winter wheat.It could improve the nitrogen use efficiency in the presence of water.Theuptake of labeled nitrate-N in the surface accounted for3.53%of total N uptakeequally,were greater than in the deeper layer,and deep irrigation and fertilization had nosignificant effect on it.（6）In the whole growth period of winter wheat,adequate soil moisture was necessaryto ensure the growth of winter wheat.The influence of evapotranspiration,rainfall and cropabsorption decreased with increasing soil depth. The corresponding depth irrigationsignificantly increased the lower soil water content within45cm.