Effects of Different Nitrogen Fertilizer Management Practices on Wheat

Transcription

1 Journal of Integrative Agriulture Advane Online Publiation 2014 Doi: /S (14) Effets of Different Nitrogen Fertilizer Management Praties on Wheat Yields and N 2 O Emissions from Wheat Fields in North China LIU Ya-nan 1, LI Ying-hun 2, PENG Zheng-ping 1, WANG Yan-qun 1, MA Shao-yun 1,GUO Li-ping 2, LIN Er-da 2, HAN Xue 2 1 College of Resoures and Environmental Sienes, Agriultural University of Hebei, Baoding , P.R.China 2 Institute of Environment and Sustainable Development in Agriulture, Chinese Aademy of Agriultural Sienes/ Key Laboratory of Agriultural Environment, Ministry of Agriulture of P.R. China, Beijing , P.R.China Abstrat Nitrogen (N) is one of the maronutrients required for plant growth, and reasonable appliation of N fertilizers an inrease rop yields and improve their quality. However, exessive appliation of N fertilizers will derease N use effiieny and also lead to inreases in N 2 O emissions from agriultural soils and many other environmental issues. Researh on the effets of different N fertilizer management praties on wheat yields and N 2 O emissions will assist the seletion of effetive N management measures whih enable ahieving high wheat yields while reduing N 2 O emissions. To investigate the effets of different N management praties on wheat yields and soil N 2 O emissions, we onduted field trials setting up 5 treatments of no N fertilizer (CK), farmers ommon N rate (AN), optimal N rate (ON), 20% redution in optimal rate+diyandiamide (ON80%+DCD), 20% redution in optimal rate+nano-arbon (ON80%+NC). The stati losed hamber gas hromatography method was used to monitor N 2 O emissions during the wheat growing season. The results showed that there were obvious seasonal harateristis of N 2 O emissions under eah treatment and N 2 O emissions were mainly onentrated in the sowinggreening stage, aounting for % of the overall emissions. Compared with AN, N 2 O emissions were dereased by 23.1, 45.4 and 33.7%, respetively, under ON, ON80%+DCD and ON80%+NC, and emission fators were delined by 21.4, 64.3 and 32.1%, respetively. Wheat yields was inreased signifiantly under ON80%+DCD and ON80%+NC by 12.3 and 11.9%, respetively, relative to AN while there was no signifiant hange in yield in the ON treatment. Compared with ON, overall N 2 O emissions were dereased by 29.1 and 13.9% while wheat yields improved by 18.3 and 17.9% under ON80%+DCD and ON80%+NC, respetively. We therefore reommend that ON80%+DCD and ON80%+NC an be referred as effetive N management praties inreasing yields while mitigating emissions. Key words: Diyandiamide, Nitrous Oxide Emissions, N Fertilizer Management, Nano-arbon, Wheat Yields INTRODUCTION Nitrous Oxide (N 2 O) is one of the important greenhouse gases (GHG). The IPCC Fifth Assessment Report indiated that the atmospheri onentration of N 2 O has reahed 324 ppb, whih is 20% higher than pre-industrial levels (IPCC 2013). It is estimated that 65% of the total N 2 O emissions were released from soils (Mosier and Kroeze 2000) and N fertilization ontributed about 36% of the diret N 2 O emissions from LIU Ya-nan, smileliugirl@163.om; Correspondene LI Ying-hun, Tel: , liyinghun@ami.a.n; PENG Zheng-ping, Tel: , pengzhengping@sohu.om

2 worldwide agriultural soils (Mosier et al. 1998). Studies have shown that N 2 O emissions ourred mainly due to the appliation of syntheti N fertilizers (Huang et al. 2011). In the North China Plain as one of the ountry's major grain produing areas, exessive appliation of N fertilizers is prominent, partiularly in high-yielding wheat and maize prodution zones with an average amount of kg N hm -2 whih far more exeeds the rop N requirements (Chen et al. 2006). Reduing N 2 O emissions from agriultural soils has drawn great attention as global warming intensifies, and the urrent researh on N 2 O emission mitigation measures fouses on long-lasting fertilizers or organi fertilizers, the implementation of onservation tillage and fertilizers added with nitrifiation inhibitors (NI) (Oenema et al. 2005; Asing et al. 2008; Huang et al. 2011). Diyandiamide (DCD) is one type of highly effetive NI. Nie et al. (2012) reported that addition of DCD in ombination with optimized N rate and water management resulted in a derease of % and % respetively in N 2 O flux peak and umulative N 2 O emissions ompared with onventional praties. In the rie-wheat rotation eosystem, relative to the ontrolled group with only urea, appliation of urea mixed with DCD for wheat ould redue N 2 O emissions by 49% in the wheat growing season and by 18% in the rie growing season (Majumdar et al. 2000, 2002). Nano-arbon (NC) is a new type of fertilizer synergist and is found to be able to improve rie yield by 10.2% and N agronomi effiieny by 40.1% while minimizing N losses when added into urea ompared to urea appliation alone (Wang et al. 2011). Nano arbon is a kind of modified arbon with low ignition point and non-ondutivity. Its size is 5-80 nm, having small-size effet, surfae effet and adsorption and other features. Nano arbon an filter toxi gases and harmful organisms and is urrently widely used in the researh field of new fertilizers whih aim to improve rop yields and fertilizer use effiieny. However, it is not lear whether nano-arbon ould also offer N 2 O emission redution potential, espeially ompared with DCD. There have been few studies on the effets of fertilizers added with NC on N 2 O emissions and rop yields, nor the effets of different N management praties in the wheat and maize rotation ropping system in north China plain. In this ontext, we will investigate the effets of different N management praties on N 2 O emissions and wheat yields based on the measurement of N 2 O flux during the winter wheat growing season using the methods of stati hamber/gas hromatogram in a field experiment. We aim to provide suggestions on N management praties for wheat prodution in north China that an ahieve high and stable prodution, improve N use effiieny while dereasing N 2 O emissions. RESULTS N 2 O flux As shown in Fig. 1, N 2 O flux in the sowing - greening stage generally followed the similar trends: rising first before dereasing. Within the 30 d following wheat sowing, N 2 O emission flux of eah treatment showed an order of AN>ON>ON80%+NC>ON80%+DCD>CK, implying that dereasing N fertilizers an lower N 2 O flux, espeially with the addition of DCD and NC. N 2 O flux peaked in the 11 th day at

3 Air temperature ( ) and μg m -2 h -1 respetively under the AN and ON treatments. The N 2 O flux peaks under the treatments of ON80%+DCD and ON80%+NC were delayed 2 d ompared with AN and ON treatments, and were 46.9 and 22.6% lower than AN and 37.7 and 9.1% lower than ON. N2O Flux(µg N m -2 h -1 ) Base fertilizer Topdressing CK AN ON ON80%+DCD ON80%+NC Days after seeding(d) Fig. 1 Impats of different N fertilizer management praties on N 2 O flux Fig. 1 and Fig.2 show that the temperature dereased one month after wheat sowing when winter ame, and N 2 O emission flux in all treatments delined to less than 50 μg m -2 h -1 with relatively little variations. Topdressing and irrigation was performed in the greening stage (175 d after sowing) in the following year. During this period of rapid wheat growth, fast uptake and utilization of soil N ourred, resulting in the seond peak of N 2 O flux in the week after topdressing under AN and ON. The N 2 O flux peak was measured and μg m -2 h -1 respetive in the treatments of AN and ON, whih dereased by 60.9 and 75.8% from the winter peak levels. Due to the ontrolled-release effets of DCD and NC on N nutrients, there was no apparent N 2 O flux peak under ON80%+DCD and ON80%+NC. In later stages, large amounts of soil N were absorbed and utilized for wheat growth along with rising temperature, leading to minor hanges 35 in N 2 O fluxes under all treatments Days after seeding (d) Days after seeding (d) Air temperature( ) Fig.2 Temperature hange during wheat growing season

4 Cumulative N 2 O emissions from whole season and emission fators Table 1 shows that, ompared with CK, total N 2 O emissions inreased by 143.0, 86.9, 32.6 and 61.0% under AN, ON, ON80%+DCD, ON80%+NC, respetively, with those under AN, ON, ON80%+NC reahing signifiant levels (P<0.05). Overall N 2 O emissions dereased by 23.1, 45.4 and 33.7% respetively under ON, ON80%+DCD, ON80%+NC relative to AN, all reahing signifiant levels (P<0.05), while emission fators dereased by 21.4, 64.3 and 32.1%, respetively. Compared with ON, total N 2 O emissions delined by 29.1 and 13.9% and emission fator dereased by 54.5 and 13.6% under ON80%+DCD and ON80%+NC, respetively. The results imply that reduing N appliation rate an derease total N 2 O emissions from wheat fields, lower N 2 O emission fators, whih is more effetive when ombined with DCD and NC addition. Table 1 Total N 2 O emissions from wheat fields and emission fators Treatment Change Change Change Emission Total N 2 O emissions relative to CK relative to AN relative to ON fator (kg N hm -2 ) (%) (%) (%) (%) CK 0.565±0.069 d AN 1.374±0.218 a ON 1.057±0.095 b ON80%+DCD 0.750±0.112 d ON80%+NC 0.911±0.143 b Note: Total N 2 O emissions in the table are expressed as means±standard deviation; different letters following numbers show signifiant differene at 0.05 level. The same as below. Cumulative N 2 O emissions from eah wheat growing stage N 2 O emissions under different N management praties have obvious seasonal variation harateristis (Fig. 3). It an be observed that under all treatments umulative N 2 O emissions of eah growing stage gradually delined along the growth of wheat. N 2 O emissions during the sowing-seedling stage represented 25.5, 39.9, 42.8, 31.2 and 39.6% of total N 2 O emissions from the wheat growth period while those from the seedling-greening stage aounted for 29.1, 28.2, 22.2, 27.0 and 18.5% under CK, AN, ON, ON80%+DCD and ON80%+NC, respetively. N 2 O emitted after the greening stage aounted for less than 45.4% of overall emissions in all treatments. These findings indiate that N 2 O emissions were generally onentrated in the sowing-greening stage, aounting for % of the total and that N 2 O emissions from the sowing stage were higher than the seedling-greening stage due to basal N fertilizer appliation. N 2 O emissions from the seedling-greening stage generally followed AN>ON>ON80%+NC>ON80%+DCD>CK while there were no obvious differenes for later growing stages. Suh findings imply that reduing the amount of N fertilizers is onduive to avoid N 2 O emissions and redution in N rates at early stages is more effetive than at latter stages.

5 N2O umulative emissions(kg N hm -2 ) a a b b b a ab b a b Sowing-seedling stage Greening-jointing stage Filling-maturing stage a ab b Seedling-greening stage Jointing-filling stage a b b b 0 CK AN ON ON80%+DCD ON80%+NC Treatments Fig. 3 Effets of different N management praties on N 2 O emissions during the different wheat growth stages Wheat yields, grain quality and N uptake As an be seen from Table 2, the appliation of N fertilizers signifiantly inreased the number of effetive paniles, grains per panile, thousand-grain weight, grain yield and N uptake of winter wheat and there was no signifiant differene on the number of effetive paniles and grains per panile between different treatments. Relative to AN, thousand-grain weight inreased signifiantly by 4.20 g under ON80%+DCD and wheat yield enhaned signifiantly by 12.3 and 11.9% under ON80%+DCD and ON80%+NC, respetively, while no signifiant hange in yields ourred under ON. Compared with ON, thousand-grain weight inreased signifiantly by 4.35 g under ON80%+DCD but saw little variation under ON80%+NC; however, wheat yields both inreased under ON80%+DCD and ON80%+NC by 18.3 and 17.9%, respetively. These results show wheat yields were not negatively impated by the 20% redution in N rates but ould be improved by adding NC or DCD into N fertilizers with the later was slightly more benefiial to yield inrease.

6 Table 2 Wheat yields, grain quality and N uptake Effetive panile Treatment number (10k hm -2 ) Grain number per panile Thousand grain weight(g) Yield (kg hm -2 ) N uptake in Grains (kg hm -2 ) NUE (%) CK ±47.16 b 32.05±0.60 b 32.23± ± ±9.73 AN ±11.79 a 41.98±1.03 a 36.79±0.85 b ± b ±10.85 ab 19.0 b ON ±30.66 a 40.72±0.93 a 36.64±1.51 b ± b ±29.25 b 16.0 b ON80%+DCD ±11.79 a 40.38±0.98 a 40.99±0.95 a ± a ±41.75 a 42.9 a ON80%+NC ±16.51 a 40.83±1.94 a 37.98±1.33 b ± a ±38.97 a 35.9 a Appliation of N fertilizers inreased N uptake over ground by % from CK treatment. N uptake under ON80%+DCD and ON80%+NC enhaned by 5.6 and 4.1% respetively ompared to the AN treatment and by 15.7 and 14.1% respetively ompared to the ON treatment. The Nitrogen use effiieny (NUE) of ON80%+DCD and ON80%+NC were 42.9 and 35.9%, respetively, whih were signifiantly higher than that of AN and ON treatments. However, there was no differene in NUE between AN and ON. DISCUSSION N 2 O emissions under different N management praties exhibited obvious seasonal variation harateristis and were onentrated in the seedling-greening stage, aounting for % of the total emissions, whih orresponds to the findings by Ma et al. ( 2007 ). But there are other studies indiating that N 2 O emissions from the wheat greening-maturing stage was higher than from the seedling- greening stage, whih may be related to the speifi basal/topdressing fertilizer ratio, temperature, preipitation and other fators. In our trial, there was heavy preipitation within the month following wheat sowing, providing relatively adequate soil moisture and suitable soil temperature for seedling (Fig. 2). Still, the main reason may lie in that the N uptake was limited by the slow growth of wheat in the seedling stage albeit adequate soil N ontent, therefore providing rih substrates for nitrifiation and denitrifiation. Suh favorable environment stimulated the ativity of relevant miroorganisms and was thus onduive to N 2 O generation. By fitting the relationships between N 2 O flux and soil moisture, we drew the following urves for eah treatment: y=0.0057x (R=0.723*) ; y=0.0062x ( R=0.670* ); y=0.0444x ( R=0.561* ); y=0.0294x (R=0.575*) (P<0.05).The N 2 O flux is positively orrelated with soil moisture, but its relationship with air temperature is not evident. This finding is onsistent with the results reported by Xu et al. (2001). We an therefore reommend reasonable adjustment of basal/topdressing ratios of N fertilizers to be adopted based on periodi harateristis of soil moisture and N 2 O emissions. Controlling the overall N rates to meet the need for rop growth, reduing the amount of basal N fertilizers at the early stages of slow rop growth, and reasonable topdressing at later stages, an help minimize N loss and environmental pollution.

7 Compared with AN, ON80%+DCD treatment not only improved wheat yield by 12.3%, but also redued N 2 O emissions by 45.4%. Relative to ON, the total N 2 O emissions was dereased by 29.1%, the emission fator lowered by 54.5%, and the wheat prodution inreased by 18.3%. We an therefore onlude that the ON80%+DCD treatment ould redue both N 2 O emissions and emission fators while maintaining yield levels. Under the onventional tillage, the umulative N 2 O emissions in the appliation of urea and DCD were signifiantly redued by 29.5% in omparison to the urea treatment, wheat yield inreased by 7.51% (Ma et al.2013). Mixing DCD into N fertilizers an signifiantly redue N 2 O fluxes ( Fig. 1 ) and overall N 2 O emissions (Table 1 ) within the month after wheat sowing, whih may be attributed to the inhibiting effets of DCD on the ativity of ammonia-oxidizing bateria or relevant enzymes, effetively delaying oxidization proess that transforms NH + 4 -N to NO - 3 -N (Di et al. 2009; Guo et al.2013). Maintaining a high soil NH + 4 -N ontent for a longer time by regulating the rapid onversion of soil N an effetively alleviate NO - 3 -N aumulation and leahing losses as well as redue N 2 O emissions (Chen et al. 2008; Fangueiro et al. 2009). Other studies reported that addition of DCD in N fertilizers an not only derease soil N 2 O emissions by 39% during wheat growth season (Ding et al. 2011), but also signifiantly redue N 2 O emissions from rie paddies (Li et al. 2009). The inhibiting effets of DCD on N 2 O emissions are more evident at the early wheat growth stages than latter stages (Fig. 1, Fig. 3), probably due to the onsistent low temperature (below20 ) after wheat sowing whih extended the effetiveness of DCD. Studies (Kelly et al. 2008) show that the half-life of DCD at 20 is d, whih explains the signifiant effets of DCD on lowering N 2 O flux within the 30 d following sowing. After this period, there was no signifiant differene on N 2 O flux between the treatments. Moreover, the temperature rose quikly in the wheat greening stage and was onduive to rapid N uptake by wheat. As a result, N 2 O emissions from the later growth stages were relatively low with little variations. Li et al. (2009) also pointed out that DCD is more effetive in inhibiting early-stage N 2 O emissions in rie paddies. In addition to reduing N 2 O emissions by 33.7 and 13.9% ompared to AN and ON respetively, the ON80%+NC treatment also inreased wheat yields by 11.9 and 17.9% and dereased the emission fators by 32.1 and 13.6%. This arrangement saved expenses on N fertilizers and ensured wheat prodution, thereby reduing the risk of ontamination aused by exessive appliation of N fertilizers. NC dissolve quikly in water when applied to soils and an fix soil NH + 4 for its strong adsorption ability, whih redues the substrate for nitrifiation and denitrifiation and meantime prevents and ontrols the exretion of N 2 O gas and enhanes N uptake by plant (Ma et al. 2009). Many studies found that nano-arbon had the potential to promote maize seed germination and root growth (Wang et al. 2013) and to improve rie yields and N use effiieny (Wang et al. 2010). However, there have been few studies on the mehanism of the effets of nano-arbon on wheat prodution and N 2 O emissions. It is likely that addition of nano-arbon improved wheat soil miro-environment, slowed down the soil nitrifiation and denitrifiation proess and enhaned N nutrient uptake, thereby reduing N 2 O release. Understanding the speifi mehanism of nano-arbon requires further researh.

8 Sine there are signifiant orrelations between N 2 O emissions and the amount of N applied (Eihner 1990; Bouwman 1996), N 2 O emission fators are widely used in the preparation and evaluation of regional and global inventories of farmland N 2 O emissions. Emission fators under the ON80%+DCD and ON80%+NC treatments were 0.10 and 0.19%, signifiantly lower than those under onventional praties and those reported for the wheat growth season ( %) in the maize-wheat rotation system in the North China Plain (Ding et al. 2007). The emission fator of N 2 O in our study is lower than the default value (1.00%) suggested by the IPCC in ompiling national GHG emissions inventories (IPCC 2006). The emission fators are also determined by other fators inluding soil texture, moisture, mirobial ativity, fertilizer type, quantity and appliation manner. The NUE of ON80%+DCD and ON80%+NC inreased by 23.9 and 16.9%, respetively, ompared to AN. N aumulation in grain aounted for 70-73% of the overall N aumulation by aboveground plant, while the N aumulated in straw ( kg hm -2) ) was assumed to totally return to soils sine straw was retained in land after harvesting. All straw of the the preeding rop maize was inorporated to soil, whih brings about kg N to per hetare of soil (Zhang et al. 2006). During the wheat growth season, soil N supplying ability was strengthened. He et al. (2011) has shown that nitrogen dry and wet deposition in the whole wheat growing season amounted to 39.2 kg hm -2, providing effetive nitrogen soure for wheat growth. N aumulation in grain were almost equal to the N quantity from fertilization under both ON80%+DCD and ON80%+NC, indiating a higher NUE and better soil sustainable use under these two treatments. Taking into aounts the effets on N 2 O emissions redutions, yield response of wheat and N 2 O emission fators, ON80%+DCD and ON80%+NC praties an be reommended as better N management praties that inrease yields while mitigating N 2 O emissions. CONCLUSION N 2 O emissions under different N management praties have obvious seasonal harateristis. N 2 O emissions under all treatment were onentrated on the sowing-greening stage, aounting for % of total emissions from the whole wheat growth period. We suggest that N 2 O emissions from wheat prodution an be redued through the adjustments of the basal/topdressing ratio and postponing N to a later stage to improve N uptake and use effiieny. A 20% redution in optimal rates of N fertilizers mixed with DCD or NC ould deliver obvious benefits on yield improvement and emission redution, and an be reommended as preferable fertilizer management praties in guaranteeing future food seurity and addressing limate hange.

9 MATERIALS AND METHODS Site desription The experimental site (N38 49, E ) is situated within the Siene and Tehnology Park of Agriultural University of Hebei in Wurao township, Baoding, Hebei Provine. This area has a temperate monsoon limate with old and dry winters, hot and rainy summers. The average annual temperature is 12, the annual sunshine hours are 2660 h, and the frost-free period is 210 d. The soil is lassified as fluvo-aqui soil and key properties are: ph 8.7, total N 1.26 g kg -1, alkali-hydrolyzable N mg kg -1, available phosphate (P) mg kg -1, available potassium (K) mg kg -1 and organi matter g kg -1. Winter wheat ultivar is Henong 5274 developed by the rop geneti breeding team in Agriultural University of Hebei. Experiment design Five experimental treatments were set up: CK (the ontrol, no N appliation), AN (farmers ommon pratie, N rate is 285 kg hm -2 ), ON (optimal N rate, N rate is 225 kg hm -2 ), ON80%+DCD (20% redution in optimal N rate added with DCD, N rate is 180 kg hm -2, DCD is applied at a rate of 5% of the applied N (w/w), ON80%+NC (20% redution in optimal N rate added with NC, N rate is 180 kg hm -2, NC is applied at a rate of 0.3% of the total applied fertilizer(w/w)). The annual appliation rates of P and K fertilizers in the forms of alium superphosphate (P 2 O 5 ontent 16%) and potassium sulfate (K 2 O ontent 60%) were 750 kg hm -2 and 250 kg hm -2, whih were kept idential for all treatments. All P and K fertilizers and 50% of N fertilizers (urea with N ontent of 46%) were applied as basal and the remaining 50% N fertilizers were applied as topdressing in the greening-jointing stage referring to the first spring irrigation. Both DCD and NC were applied in basal and topdressing fertilizers. The plot size was 30 m 2 (8 m 3.75 m). The plots were arranged in a randomized omplete blok experimental design with 3 repliates. Land preparation was onduted and wheat was sown by mahine on Otober 10, 2012 with a seed rate of kg hm -2. The wheat harvest took plae on June 20, Exept for fertilization, other on-farm management praties are kept onsistent with farmers traditional management methods. Gas sampling and measurement The stati losed-hamber method was used for olleting gas samples from wheat sowing to harvest. Gas samples were taken one at an interval of 7 d in general, eah day in the 15 d following fertilization and eah day in the 3-5 d following preipitation. Gas olletion was performed in the morning between 09:00 and 11:00 and samples of 30 ml hamber air were olleted at 0, 10 and 20 min after losure. In the meantime, air temperature in the hamber was measured. Gas onentrations were analyzed using a gas hromatography (Agilent 7890A). The olumns are paked with Porapak Q and the olumns temperature is 70. The arrier gas is N 2 and the working temperature of eletroni detetor (ECD) is 330. Calibration

10 of the gas hromatography took plae eah time prior to gas measurement using standard gas supplied by the National Center of Standard Measurement and the relative error is less than 2%. Data disposal and alulation methods N 2 O flux is alulated using the equation : F=ρ V/A Δ/Δt 273/(273+θ) 60 Where, F is the N 2 O emission flux(µg N m -2 h -1 );ρ is the density of gas in standard state(kg m -3 ); V is the volume of the stati hamber (m 3 ); A is the bottom area of the stati hamber (m 2 ); Δ/Δt defines the hange rate of N 2 O onentration within the stati hamber per unit time (10-9 V V -1 min -1 );θ is the average temperature inside the stati hamber ( ). Cumulative N 2 O emissions from eah wheat growing stage are alulated following the equation: T=Σ[( F i+1 +F i )/2] (D i+1 -D i ) 24/ Where, T is the umulative N 2 O emissions from one growing stage (kg N hm -2 ); F i and F i+1 denotes the N 2 O flux of the i and i+1 sub-sampling (μg N m -2 h -1 ) ; D i and D i+1 represents the sampling time (d) (Ji et al. 2011). Wheat growing stages are lassified as the sowing-seedling, seedling-greening, greening-jointing, jointing-filling and filling-maturing stages whih orrespond to the 0-23, , , , d respetively following wheat sowing. The emission fator refers to the perentage of N that is released in the form of N 2 O to the applied N nutrients. Double rows of 1 m areas of wheat were harvested for eah plot. The effetive paniles numbers were ounted from 50 seleted paniles. All harvested samples were threshed and grain yield was standardized at 12.5% moisture ontent. Three samples were weighted to get the average thousand-grain weight for eah plot. The straw and grains from some plants were dried, weighted and then rushed to test the N ontent using H 2 SO 4 -H 2 O 2 Kjeldahl Digestion Method. NUE (%) = (N aumulation in aboveground plant with N treatment-n aumulation in aboveground plant without N treatment)/n appliation rate 100% Exel 2003 was used for data disposal. Some variables,suh as N 2 O flux, umulative N 2 O emissions during the different growth stages of wheat, total N 2 O emissions, yield and it s onstitution, N aumulation in wheat, were statistially analyzed by the Software of SPSS18.0. Aknowledgements This researh is supported by the Chinese Ministry of Siene and Tehnology (2013BAD11B03), the National Natural Siene Foundation ( ) and The Agriultural Siene and Tehnology Innovation Program of CAAS.

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