Effects Of Nitrogen Topdressing Stage On Fate Of Fertilizer Nitrogen And Gaseous N Loss In Winter Wheat

Nitrogen （N） plays a very important role in grain production. However, too much orirregular application of N fertilizer may reduce the efficiency of N. Since the1960s, theclimate appeared the trend of less rainfall and rising temperatures. Water shortage has becomea key factor constraining the sustainable development of the agricultural production in theregion. Water use efficiency has become the important research issues of Huang-Huai winterwheat cultivation. In this study, we established the field15N-microplot experiments, usedventing method and the closed static chamber measurement, quantitative studied effects of Ntopdressing stage on fate of fertilizer N and gaseous N loss in winter wheat under theirrigation and rainfed conditions, in order to explore the relationship between N topdressingstage as well as water management and the fate of fertilizer N as well as gaseous N loss. Itprovided the theoretical basis for reducing the N loss and raising the utilization efficiency offertilizer and water. The main results were as follows:1The effects of N topdressing stage on the N accumulation, translocation and distribution inwheat plants.With the postpone of nitrogen application, the N content of wheat grain increased, butthe N content of leaf and stem decreased. The total N accumulation amount （TNAA） in plantwas highest dressing at jointing stage （JT）. N application at JT was beneficial to increase theTNAA in grains, reduce the TNAA in vegetative organs, to promote the transportation of N invegetative organs into grain.Under different N topdressing stage conditions, N productive efficiency and N harvestindex of winter wheat were highest dressing at JT. N application at JT was more conducive topromoting the N absorption of the strong gluten wheat variety, and increasing the Nutilization of the middle and weak gluten wheat variety.With the postpone of nitrogen application, the percentage of the TNAA derived fromfertilizer decreased. Delayed N topdressing stage, the percentage of the TNAA derived from basal dressing fertilizer increased, the percentage derived from topdressing fertilizer reduced.2The effects of N topdressing stage on fertilizer N residues and the fate of fertilizer NWith the postpone of nitrogen application, the residues of fertilizer N in0-100cm soilincreased. Compared to N application at stem elongation （SE） and booting stage （BT）, as Napplication at JT after water irrigation, the residues of fertilizer N in20-60cm soil werehigher.The fate of fertilizer N in wheat season showed as follows: under N application at SE,the rate of plants uptake from fertilizer N was44.5-49.5%; the rate of0-100cm soil residuefrom fertilizer N was31.9-35.8%; the rate of fertilizer N loss was18.6-19.7%. Under Napplication at JT, the rate of plants uptake was36.2-43.4%, the rate of0-100cm soil residuewas41.1-47.9%, the rate of fertilizer loss was15.6-16.0%. Under N application at BT, therate of plants uptake was33.1-41.5%, the rate of0-100cm soil residue was42.0-49.7%, therate of fertilizer loss was16.5-17.3%. Comprehensive analysis of plants uptake, soil residueand the fertilizer loss obtained: under N application at JT content, the fate of fertilizer N wasmore balanced.3The effects of N topdressing stage on ammonia volatilization （AV） from topdressingfertilization in irrigated and rainfed wheat fieldsUnder rainfed conditions, the AV from topdressing fertilization in wheat fields occurredmainly during5to25days after fertilization. With the delay of N topdressing stage from SEto JT, the peak value of AV rate increased and was ahead, and a small amount of rainfall afterfertilization increased AV rate; with the delay of N topdressing stage to BT, the peak value ofAV rate reduced. The rate of AV loss was24.82-25.32%,25.07-25.42%and13.72-15.02%atSE, JT and BT treatments, respectively. In the three N topdressing stage treatments, the AVrate from topdressing fertilization in irrigated wheat fields did not change significantly. N lossvia accumulated AV was0.40to0.55kg N·ha^-1, only accounting for0.36-0.49%oftopdressing N.Ammonium nitrogen concentration （NH₄⁺-N） of0-10cm soil was a direct factoraffecting AV in the low soil moisture content. In the high soil moisture, water was the maincontrolling factor, but was not NH₄⁺-N concentration. After irrigation, the hydrolysis ofNH4₊^-N into ammonia escaped into the air and moved into10-20cm soil were carried out simultaneously, but the synchronization relationship of the hydrolysis of NH4+-N intoammonia escaped into the air and moved into20-40cm soil appeared a certain delay.Under rainfed conditions, with the delay of nitrogen topdressing stage from SE to JT,soil temperature enhanced and AV losses increased. The small amount of rainfall aftertopdressing fertilization applying at SE and JT stage could increase AV rate. But Ntopdressing stage delayed to BT could effectively use a large number of late rainfall, to reduceAV loss of rainfed wheat field.4The effects of N topdressing stage on nirous oxide （N₂O） emission from topdressingfertilization in irrigated and rainfed wheat fieldsN₂O emission from wheat field began to rise3days after fertilization, the differencewere small between different treatments and control （CK）25days after fertilization. N₂Oemission could be achieved duration of23days. The net N₂O emission under irrigationconditions was smaller than under rainfed condition. Both irrigation and rainfed conditions,soil N₂O emission flux peak and net N₂O emission fluxes increased With the postpone ofnitrogen application.Both irrigation and rainfed conditions, N₂O emission fluxes with0-10cm and10-20cmsoil nitrate N （NO3--N） concentration were significantly positively related.0-20cm soilNO₃^--N concentration was the determining factor of N₂O emission from fertilizer nitrogen.NO₃^--N released N₂O by the nitrification and denitrification into the air and moved20-40cmsoil was carried out simultaneously.Irrigation and rainfall significantly affected N₂O emission. Soil moisture and N₂Oemission were more complex, only soil moisture under suitable conditions could N₂Oemission increase. With the postpone of nitrogen application, soil temperature enhanced andN₂O emission flux increased. The correlation analysis showed that the temperature of10cmsoil was the determining factor of N₂O emission.