評估施用氮肥對水稻灌溉系統(tǒng)中CH4和N2O排放的影響翻譯解析

1、Assessing fertilizer N placement on CH4 and N2O emissions in irrigated rice systems ABSTRACT ：Improved N fertilizer management practices can increase rice yields and mitigate global warming potential (GWP). While banding N has been shown to have positive effects on yield and nitrogen use efficiency

2、(NUE),there is little information on how it affects green house gas (GHG) emissions from flooded rice systems. We tested the hypothesis that in continuously flooded rice systems where GWP is dominated by CH4 emissions , deep placement of urea in bands would reduce CH4 and N2O emissions. Rice yields

3、and GHG emissions were measured from three field experiments which had three treatments : (1) no N(N0), (2) urea broadcast(U-BR) on soil surfaceand (3) urea banded at 7.5 cm soil depth (U-BA). All urea was applied in a single application -1before floodi ng in preparati on for pla nti ng at N rates o

4、f 143-50 kg N ha . Throughout the ricegrowing season GHG emissions were measured using a vented flux chamber and gas chromatograph. Across all fields , N fertilizer application increased yield on average by 121%.Between the N placement methods, grain yields and NUE(37kg grain kg - 1 ) were similar.

5、DailyN2O emissions were low to negative and did not differ among treatments. CH4 emissions were themajor source of GWP emissions and cumulative emissions ranged from 6.3 to 297 kg CH4-C ha-1-1seasonamong fields. While in some cases fertilizer N increased CH4 emissions, there was no effect of N place

6、ment on them.評估氮肥深施對水稻灌溉系統(tǒng)中CH4和20排放的影響摘要：提高氮肥管理措施能夠增加水稻產(chǎn)量且減輕全球變暖趨勢（GWP）。帶狀施氮已對產(chǎn)量和氮肥利用率（NUE）產(chǎn)生積極影響，但在淹水水稻系統(tǒng)下，如何影響溫室氣體（GHG）排放的信息還很少。我們檢驗假設(shè)在持續(xù)淹水水稻系統(tǒng)中 GWP 主要由 CH4 排放占主導(dǎo)地位，尿素 深施會降低CH4和N2O的排放。3個田間試驗各3個處理測定水稻產(chǎn)量和 GHG排放：（1） 不施氮（NO），（2）尿素播撒（U-BR）在土壤表層，（3）在7.5cm 土壤深度處尿素帶施 （U-BA）。 在準(zhǔn)備種植淹水之前一次性施用所有尿素，施氮量為143-150

7、 kg ha-1。利用排放通量室和氣相色譜儀測定水稻整個生育期GHG排放量。在所有 田間試驗中，施用氮肥平均產(chǎn)量增加了121%。氮肥深施的方法、作物產(chǎn)量和NUE （每Kg施氮量產(chǎn)37Kg糧食）都有類似結(jié)果。每天N2O排放量很低，且和其他處理之間沒有差別。CH4排放是GWP的主要來源，且每季每公頃CH4累積排放量范圍為 6.3-297Kg。雖然在某些情況下，施氮增加了CH4的排放，但氮肥深施對CH4的排放并沒有影響。1. IntroductionRice is the largest single source of calories for over 3.7 B people and rice

8、 cultivation is the largest single use of land for food (GRISP,2013). According to FAO projections, feeding a world population of 9 B in 2050 will require raising overall food production by 70% (FAO, 2009). Given the currentworld population and estimated projections, rice production needs to increas

9、e annually by 1.2-2.4% during the next decade to meet global demand (GRISP, 2013, Ray et al., 2013). However at the current rate of grain yield increase, supply will not meet the demand (Grassini et al., 2013) and thus, production systems need to be more productive while at the same time reducing ne

10、gative environmental impacts.對于超過 37 億人來說，水稻是最大的單一熱量來源，水稻種植也是最大的糧食土地利用(GRISP2013)。根據(jù)FAO (聯(lián)合國糧食與農(nóng)業(yè)組織)預(yù)測， 到2050年要養(yǎng)活90億的世界 人口，需要提高糧食產(chǎn)量 70% ( FAO, 2009)?？紤]到目前世界人口和預(yù)測人口，在接下來的 10 年里，水稻產(chǎn)量每年要增加1.2-2.4%，來滿足全球需求 (GRISP,2013, Ray et al., 2013)。然而，在目前糧食產(chǎn)量增長率上來看，供不應(yīng)求( Grassini et al., 2013 )，因此，生產(chǎn)系統(tǒng)需要 更高的生產(chǎn)力，與此同

11、時要降低對環(huán)境的消極影響。Doberma nn (2004) estimated that for each ton of grain yield produced, rice requires 15-20 kg Nwhen all other factors for growing rice are not limiting. However, increasing N rates to achieve higher yields can also lead to higher N 2 O emissions (Pittelkow et al., 2014). Recent results

12、of meta-analysis of N fertilizer effects on GHG emissions showed that N fertilizer-induced N 2 O emission factor during the rice growing season was 0.21% for continuously flooded fields and 0.40% for fields with drained periods (Linquist et al., 2012). A higher N 2 O emission factor of 0.31% was rep

13、orted by Akiyama et al. (2005) for both organically and synthetically fertilized rice fields under all water management practices. Likewise, addition of fertilizer N influences CH 4 emission through enhanced CH 4 oxidation, increased transport for CH 4 and more carbon substrate for CH 4 production (

14、Schimel, 2000; Wassmann and Aulakh, 2000). Field studies report variable results on the effect of N fertilization on CH 4 emission however, based on a meta-analysis, Linquist et al. (2012) concluded that impacts of N fertilizer on growing season CH 4 emissions are N rate-dependent, where low to mode

15、rate N rates increased emissions and high N rates decreased emissions.Dobermann ( 2 0 04 )預(yù)測在所有其他因素都不限制水稻生長時，每生產(chǎn)1t 糧食，水稻需要15-20kg N 肥。然而增加氮肥用量實現(xiàn)高產(chǎn)也能導(dǎo)致 N2O 的高排放( Pittelkow et al., 2014 )。 氮肥對溫室氣體排放的Meta分析最新結(jié)果表明：水稻生育期間氮肥誘導(dǎo)N2O排放系數(shù)，在持續(xù)淹水條件下為 0.21%，在排水期為 0.40%(Linquist et al., 2012)。 Akiyama et al.(2005)

16、 報道在所有水分管理方式下，稻田有機(jī)地綜合地施用肥料，N2O高排放系數(shù)為0.31%。同樣地，氮肥的增加影響 CH4排放，主要通過加強(qiáng)CH4氧化、增加CH4遷移和更多的CH4碳源物(Schimel, 2000; Wassmann and Aulakh, 2000)。很多報道表明施氮對 CH4排放的影響有不 同的結(jié)果，然而基于 Meta分析，Linquist et al. (2012)總結(jié)：氮肥對生育期 CH4排放的影 響取決于施氮量，低施氮量增加CH4排放，高施氮量降低 CH4排放。In the same review, Linquist et al. (2012) found that dee

17、p placement or banding of fertilizer N in continuously flooded rice systems reduced CH 4 emissions by 40% and increased N 2 O emissions by 18%. Given that N 2 O emissions are relatively low in rice systems, the large decrease in CH 4 emissions could potentially lead to a net reduction in GWP. The re

18、ason suggested for reduced CH4 emissions was that deep-placed fertilizer N stimulates CH 4 oxidation through the concentration of N in localized areas. However, the amount of data available for this analysis was small suggesting the need for further study before conclusions could be drawn.在同一綜述中， Li

19、nquist et al. (2012)表明：在持續(xù)淹水水稻系統(tǒng)中，氮肥深施或帶施降低 了 40%的CH4排放，并且增加了 18%的N2O排放。鑒于水稻系統(tǒng)中相對較低的N2O排放，CH4排放大量減少可能潛在導(dǎo)致GWP降低。提出降低CH4排放的原因：氮肥深施通過局部區(qū)域的氮濃度來刺激 CH4 氧化。 然而，可用于分析的數(shù)據(jù)量很少，建議需要進(jìn)一步深入研 究來得到之前的結(jié)論。Deep placement of N can also lead to increased NUE because it minimizes N losses as the ammonium is protected from

20、 nitrification / denitrification in anaerobic soil layers (Savant and Stangel, 1990). While some studies find no effect of deep N placement or banding of N on grain yields (Suratno et al., 1998; Setyanto et al., 2000) many studies report grain yields and NUE increase compared to broadcast (Savant an

21、d Stangel, 1990; Schnier et al., 1993; Ingram et al.,1991; Linquist et al., 2009).氮素深施也能增加NUE,是因為在厭氧土層中硝化/反硝化保護(hù)了氨基鹽，從而使氮素?fù)p失最小化 (Savant and Stangel, 1990)。 而有些研究發(fā)現(xiàn)氮素深施或帶施對糧食產(chǎn)量沒有影響(Surat no et al., 1998; Setya nto et al., 2000)，很多研究報道了與撒施相比糧食產(chǎn)量和NUE增加了( Savant and Stangel, 1990; Schnier et al., 1993; I

22、ngram et al.,1991; Linquist et al., 2009 )。Realizing the variable results of N fertilizer management practices on GHG emissions and rice yield, it is difficult to assume that a strategy based exclusively on rates, source or method of application will promote both low N 2 O and CH 4 emissions and hig

23、her yield because gas fluxes are largely influenced by fertilizer N, soil, crop and their interactions (Horwath, 2011; Chai et al., 2013) and mitigating one gas may lead to stimulating the other gas. Therefore, in field experiments we tested the hypothesis that N fertilizer banded below the soil sur

24、face would result in the lowest CH 4 and N 2 O emissions and higher grain yield relative to N that is broadcasted on the soil surface.了解到氮肥管理方式對 GHG 排放和水稻產(chǎn)量產(chǎn)生不同的結(jié)果，由于氣體通量主要受氮肥、 土壤、作物和他們的相互作用的影響( Horwath, 2011; Chai et al., 2013 ) ，且減少一個氣體可 能導(dǎo)致刺激其他氣體，所以很難假設(shè)一個促進(jìn) N2O及CH4的低排放和高產(chǎn)的完全基于用量、 來源或應(yīng)用方法的對策。因此，我們

25、檢驗假設(shè)在田間試驗中，相對于N 撒播在土壤表面，在土壤表層以下帶狀施氮會導(dǎo)致最低的 CH4和N2O排放以及更高的產(chǎn)量。2. Materials and methods2.1. Field experimentThree field trials were conducted on an experimental field located at the University of California near Davis, CA in 2012 (Field 1: 38.54 N; 121.81 W; elevation 20 m above sea level masl), a comme

26、rcial farm near Marysville, CA in 2013 (Field 2: 39.22 N; 121.54 W; elevation 23 masl), and at the Rice Experiment Station of the California Cooperative Rice Research Foundation, Inc. near Biggs, CA in 2014 (Field 3:39.46 N; 121.74 W; elevation 29 masl). Site details, including cropping history and

27、previous crop residue management are reported in Table 1.三個田間試驗：1)2012年在加州大學(xué)戴維斯附近(試驗1： 38.54 N； 121.81 W；海拔高20m)，2) 2013年在馬里斯維爾鎮(zhèn)附近的一個商業(yè)農(nóng)場(試驗2: 39.22 N； 121.54 W ；海拔高23m)，3) 2014年在加州合作水稻研究基金會的水稻實驗站， 比格斯附近的公司 (試驗 3： 39.46 N；121.74 W;海拔高29m)。試驗地細(xì)節(jié)包括種植歷史和前作殘留管理見表1。The experiments were set up as randomiz

28、ed complete block design with three to four replicates2in plots of 5.5 -55.7 m . Fertilizer N rates were 0, 150 kg N ha -1 (Fields 1 and 3) and 0, 143 kg N ha -1 (Field 2) (Table 2). The three fertilizer N treatment combinations used were: U-BR : urea N fertilizer broadcast on the soil surface , U-B

29、A: urea N fertilizer placed in a row at 7.5 cm depth and 22.9 cm apart, and N0; no fertilizer N applied. At all sites, fertilizer N was applied as a single dose and either broadcast or deeply placed in a row right before permanently flooding the field in preparation for planting. Triple superphospha

30、te (46kgP ha -1 ) and K2SO4 (22 kg K ha -1 ) fertilizers were applied before seeding to ensure these nutrients were not limiting. After fertilizer addition and flooding, pre-germinated rice seeds (varieties Table 1) were sown at a rate of 123 -68 kg seeds ha -1 . All three fields were continuously f

31、looded with flood water maintained at 6 -22 cm duri ng the grow ing seas on un til fields were drained about three to four weeks before harvest (Table 1).試驗設(shè)置為完全隨機(jī)區(qū)組設(shè)計3到4次重復(fù)，小區(qū)面積為5.5 -55.7 m2。氮肥用量為0,150 kg- 1 -1N ha-(試驗地1和3)和0，143 kg N ha-(試驗地2)(表2)。3種氮肥處理方式：U-BR: 土壤表面撒施尿素，U-BA：尿素深施深 7.5cm，兩行相距22.9c

32、m，N0：不施氮肥。所有試驗 田都一次性施用氮肥， 在種植之前的長期漬水田中在一行撒施或深施。 在播種之前施用三重 過磷酸鈣(46kg P ha-1)和©SO4(22 kg K ha-1)，并確保這些營養(yǎng)物質(zhì)沒有限制。施肥和漬水后， 播種發(fā)芽前的水稻(表1)種子123-168 kg ha-1。三個試驗地在作物生長季節(jié)都持續(xù)漬水6-22cm，直到在收獲之前三到四個星期把水排干(表1)。2.2. CH 4 and N 2 O flux measurementsMethane and N 2 O fluxes were measured daily during N fertilizati

33、on and drain events and weekly during the rest of growing season using a static vented flux chamber technique (Hutchinson and Livingston, 1993). Gas sampling occurred between 09:00 to 12:00 h and the sequence of gas measurements was randomized to avoid bias to changing air temperature.施N肥和排水過程中，每天都進(jìn)

34、行甲烷和N 2O通量測量，每周使用靜態(tài)排放通量室技術(shù)測定生長季節(jié)的其余部分 (Hutchinson and Livingston, 1993) 。在上午 9點至 1 2點之間進(jìn)行氣體 采樣,氣體的測量順序是隨機(jī)的,以避免偏見來改變空氣溫度。Flux chambers consisted of a base (29.5 cm in diameter), an extension (15.3 to 80.6 cm throughout the growing season to accommodate plants), and a lid (7.6 cm tall) all made of pol

35、yvinyl chloride (PVC) pipe.通量室包括一個底面 (直徑 29.5 cm)，一個范圍(15.3-80.6 cm，適 應(yīng)植物整個生長季節(jié))，和一個蓋子(高7.6cm)都由聚氯乙烯(PVC管道組成。The flux chamber base was placed 15 cm into the soil leaving approximately 8 cm above the soil surface. 通量室基 礎(chǔ)被 15 厘米離開大約 8 厘米以上進(jìn)入土壤土壤表面。 Two holes were made on upper sides of the base and fo

36、ur 11 cm diameter holes were drilled in the bottom of the chamber base in order to prevent restriction of water and root movement above and below the soil surface. The chamber lid had a vent tube to equalize pressure between the inside and outside of the chamber (HutchinsonandMosier,1981 ) and a fan

37、 to mix the headspace gas for one minute before sampling. Air temperature was measured by a thermocouple wire while floodwater height was measured manually by ruler and continuously using a water level sensor and logger (Global Water Inst., College Station, TX). At four equal time intervals within a

38、n hour of chamber closure, a 25 mL gas sample was taken from the enclosed flux chamber and immediately transferred into an evacuated 12-mL glass vial (Labco Ltd., Buckinghamshire, UK) with rubber septa double sealed with 100% silicon for leak-free storage prior to gas analysis . Concentrations of CH

39、 4 and N 2 O from the headspace gas samples were analyzed on a GC-2014 gas chromatograph (Shimadzu Scientific, Inst, Columbia, MD) with a 63 Ni electron capture detector (ECD) for N 2 O concentrations and flame ionization detector (FID)for CH 4 concentrations. N 2 O and CH 4 were separated by a stai

40、nless steel column packed with Hayesep D, 80/100 mesh at 75 °C isothermally. The ECD was set at 325 C°while FID was set at 250 C. A 1 m°Lheadspace gas was injected into the GC inlet port using an autosampler (Bandolero?, XYZTEK, Sacramento, CA).在上表面做 2 個小孔，底面鉆 4 個直徑為 11cm 的孔，便于水分和根系的運

41、動。通量室蓋有 一個通氣管， 來平衡通量室里外的壓力， 風(fēng)扇是為了在采樣前一分鐘混合頂端空氣。 用熱電 偶線測量空氣溫度， 用尺子并連續(xù)用水位傳感器及記錄儀測量水位。 在四個相等的時間間隔 后的一小時內(nèi)關(guān)閉， 25mL 氣體收集在通量室內(nèi)，并立即轉(zhuǎn)移到 12mL 的真空玻璃瓶中，在 氣體分析之前用100%的硅橡膠隔膜雙重密封儲存。用GC-2014氣象色譜儀分析頂端空氣的CH4和N2O的濃度，用63Ni電子捕獲檢測器（ECD檢測N2O濃度和火焰離子化檢測器（FID） 檢測CH4濃度。用純凈的色譜柱隔列 N 2 O和CH4 Hayesep D在75°C等溫地80/100網(wǎng)。ECD 設(shè)定溫

42、度為325°C, FID為250 °。自動進(jìn)樣器把1mL的頂端空氣注入到 GC進(jìn)氣口 （Bandolero?,XYZTEK, Sacramento, CA。）Fluxes of N2O and CH4 were estimated from the linear increase of gas concentration over time2based on r > 0.90 (Liu et al., 2010; Shang et al.,2011) while providing the maximum available flux data in the anal

43、ysis of gas emissions. Gas concentrations were converted to mass per unit volume (g N 2 O or CH 4 L-1 ) using the Ideal Gas Law at chamber air temperature measured during each sampling event and 0.101 MPa. Fluxes of N 2 O and CH 4 were computed as:N2O和CH4通量基于r2> 0.90估計氣體濃度隨時間線性增加，同時提供可用的最大氣體排 放通量

44、分析數(shù)據(jù)。利用理想氣體定律把氣體濃度轉(zhuǎn)換成單位體積的質(zhì)量(g N 2 O或CH 4 L-1),在每個采樣結(jié)果和0.101 MPa中測定通量室內(nèi)的空氣溫度。N2O和CH4通量公式：F=A C/ t *V/A* aWhere Fis gas flux rate for N 2 O/CH 4 (g N 2 O -N/CH 4 - Cha -1 d -1 ), deCotAstthe in crease or decrease of gas concentration in the chamber (g L -1 d -1 ), V is the chamber volume (L), A is th

45、e enclosed surface area (ha), and a is a conversion coefficient for elemental N and C (28/44for N 2 O; 12 /16 for CH 4 ). Gas fluxes which failed linearity test were not included in the data analysis and accounted for <2% of the total data set, while gas fluxes that failed significance and detect

46、ion tests were set to zero flux. A complete discussion of chamber flux method is described in Adviento-Borbe et al. (2013).計算N2O/CH4氣體通量率，A C/ 表示通量室內(nèi)氣體濃度的增加或減少，V表示通量室體積，A表示表面積，a表示元素N和C的轉(zhuǎn)化系數(shù)。不呈線性關(guān)系的氣體不進(jìn)行氣體通量數(shù)據(jù)分 析，且這些氣體占總數(shù)據(jù)集的比例小于 2%，不顯著和檢測通量測試的氣體通量設(shè)置為零通 量。 Adviento-Borbe et al. (2013) 描述了一個完整的通量方法2.3.

47、 Measurements of ancillary variablesPrior to each field experiment, soil samples were taken from 0 to 0.15 m soil layer (Table 2). At2physiological maturity, rice in a 1 m area within each treatment was harvested at 1 to 2 cm above the soil surface, separated into grain and straw components, and dri

48、ed at 60 °C to a -1constant weight. Grain yield was adjusted to 140 g kg water content. Air temperature and rainfall data were obtained from weather stations located 5 to 59 km from study sites.每個試驗之前，采集 0 到 15cm 表層土樣 (Table 2)。在生理成熟時，每個處理1 平方米地區(qū)，收獲地表1到2厘米以上的水稻，分成谷物和草，60°C烘干至恒重。籽粒產(chǎn)量含水量為140

49、 g kg-1。從氣象站獲得氣溫和降雨量數(shù)據(jù)，氣象站位于試驗田5- 59km。2.4. Data analysisAll data were subjected to no rmality tests using the Shapiro-Wilk approach and data that failedno rmal distributi ons were log-tra nsformed(P=0.000-0.224). Gree n house gas emissi ons due to Nfertilizer treatments and site as main effects and

50、 blocking and blockx N fertilizer treatments arandom effects were analyzed using PROC MIXED. and the model was fitted using the restricted maximum likelihood procedure to estimate the means and standard errors for each combination (SAS, 2010) . Analysis of repeated measures was performed using autor

51、egressive order 1 covariance to determine if means and differences of daily gas emissions changed with measurement date. One-way analysis of variance on cumulative gas emissions, crop yield and NUE among N fertilizer treatments per site was also analyzed using PROC MIXED and means of Nfertilizer tre

52、atments were compared using adjusted Tukey test at P <0.05 (SAS, 2010).用 Shapiro-Wilk 方法對所有數(shù)據(jù)進(jìn)行正態(tài)性檢驗，不呈正態(tài)分布的數(shù)據(jù)用對數(shù)轉(zhuǎn)換(P=0.000-0.224)。利用混合效應(yīng)模型(PROC MIXED分析溫室氣體排放，氮肥處理和試驗點 作為固定效應(yīng)，區(qū)組和區(qū)組x N肥處理作為隨機(jī)效應(yīng)，用最大似然方法估計為每個組合的均 值和標(biāo)準(zhǔn)誤對模型進(jìn)行擬合 (SAS, 2010)。用自回歸階 1 協(xié)方差來重復(fù)測量分析確定均值和日 常氣體排放隨測量日期而變化的偏差。對氣體累積排放量進(jìn)行單因素方差分析，利用

53、PROCMIXED分析每個試驗點氮肥處理的作物產(chǎn)量和NUE,用調(diào)整后的圖基檢驗(P <0.05)比較氮肥處理均值。Global warming potential (GWP) of N 2 O and CH 4 was calculated in mass of CO 2 equivalents (kg -1CO2 eq ha ) over a 100-year time horizon. A radiative forcing potential relative to CO2 of 296 was used for N2O and 25 for CH 4 (Houghton et a

54、l., 2001). Yield-scaled global warming potential (GWP Y ) expressed as GWP per unit mass of rice grain (kg CO 2 eq Mg grain -1 ) was comp uted by taking the ratio of GWP (kg CO 2 eq ha -1 ) and grain yield (Mg ha -1 ). Cumulative seasonal CH4 and N2O emissions were determined using linear interpolat

55、ion which included flux measurement period from tillage to harvest at each field. Unfertilized and N fertilized treatment plots were used to estimate NUE (kg kg -1 ). Nitrogen use efficiency was computed fro m the grain yield increase per unit of fertilizer N added (Dobermann and Fairhurst,2000).在10

56、0年時間里，用整個 CO2當(dāng)量(kg CO2 eq ha-1 )來計算N2O和CH4的全球變暖潛力(GWP)。輻射強(qiáng)迫潛力相對于 296年二氧化碳用于一氧化二氮和 25 CH 4(霍頓et al .,2001)。 全球變暖潛力產(chǎn)量比(GWP Y表示為每單位質(zhì)量的水稻 (kg CO 2 eq Mg grain -1 )，通過 GWP(kg CO 2 eq ha -1)和籽粒產(chǎn)量(Mg ha -1 )的比率來計算。使用線性插值測定N2O和CH4季節(jié)性累計排放量，包括在每個試驗點從耕作到收獲的通量測定周期。未施肥和N 施肥處理被用來估計 NUE(kg kg -1)。氮利用效率是增加每單位氮肥提高的谷

57、物產(chǎn)量 (Dobermann and Fairhurst,2000)。3. Results3.1. ClimateIn all fields, mean daily air temperature ranged from 12.4 to 32.8 °C during the rice growing period with the warmest mean air temperature measured in Field 3 (Fig. 1). Total annual rainfall was 138 to 466 mm (3 years) and 91% occurred du

58、ring the non-growing period.在所有試驗點，平均每天空氣溫度范圍為從 12.4 到 32.8°C， 在最熱的水稻生長期平均空氣 溫度測量在試驗點 3(Fig. 1)?？偰杲涤炅繛?138-466 毫米(3年)，且 91%的降雨不在生長期間 內(nèi)。3.2. Grain yield, crop biomass and nitrogen use efficiency Without N fertilizer, grain yields ranged from 2.9 to 11.6 Mg ha -1 with Field 2 having yields >9

59、Mg ha -1 (Fig. 2). In all fertilized N treatments, grain yield (Fig. 2) and crop biomass (data not shown)increased on average by 121% and 138% relative to N0 treatment, respectively. Across all fields, banding and broadcasting N fertilizer increased grain yield by 152% and 91%, respectively, relative to fields without N fertilizer; however, differences in grain yield between U-BA and U-B