京郊典型设施蔬菜地N2O排放规律及影响因素研究

为明确典型设施蔬菜地N2O排放规律及其影响因素,采用静态箱法,对北京郊区典型设施菜地番茄生长季进行了系统的观测,并分析了氮肥施用量、土壤温度、土壤水分对土壤N2O排放的影响。结果表明:设施番茄地N2O排放具有明显的生长季变异性,随着施肥和灌溉事件呈现多峰的动态变化规律。与农民习惯施肥处理(FP)相比,减氮施肥处理(OPT)能减少N2O排放总量41.67%,减氮施肥+硝化抑制剂处理(OPT+DCD)则能减少N2O排放总量54.46%;各处理N2O的排放系数介于0.55%～1.15%之间;土壤N2O排放与土壤湿度表现出显著的相关性,但与土壤温度未表现出明显相关性。     

温室栽培条件下N2O排放量和浓度分布对肥料和施肥的短期响应

In vegetable cultivation, the majority of N2O emissions occur after fertilization; it is therefore important to understand any factors contributing to this process. An experiment was conducted to investigate short-term N2O dynamics following topdressing in a greenhouse vegetable field in South China. During two topdressing processes, three different urea-N treatments with irrigation were conducted in May and June in a tomato (Lycopersicum esculentum) cultivation. The N2O fluxes, soil concentration profiles and soil environments at the 0-60 cm depths at 10 cm intervals were measured both immediately prior to and 5 days after topdressing. The N2O fluxes before topdressing ranged from 6.7±2.1 to 55.0±28.8 μ g N m 2 h 1 ; even higher numbers were recorded in highly fertilized plots. The NO3-N accumulation in the soil caused by vegetable cultivation during the 5 years prior to the start of the experiment, resulted in high background N2O fluxes. One day after topdressing (1 DAT) in May and June, N2O fluxes increased, which coincided with sharp increases in soil N2O concentrations at depths of 2.5 and 15 cm and in NO3-N and NH+4 -N contents at depths of 0-20 cm. From 1 to 5 DAT, fluctuations in the N2O fluxes did not harmonize with the N2O concentrations at a depth of 2.5 cm, which was attributed to different gas diffusion rates at depths of 0-10 cm. These results suggested that surface soil N and environmental conditions were crucial for determining the short-term N2O ebullitions during topdressing in greenhouse vegetable cultivation.     

农田土壤N2O排放的关键过程及影响因素

一氧化二氮 (N₂O) 作为重要的温室气体之一,在全球气候变化研究中引人关注。随着氮肥使用量的增加,农田土壤N₂O排放已经成为全球关注和研究的热点。人们普遍认为土壤硝化、反硝化过程是N₂O产生的两个主导途径,而诸如施肥、灌水等农田管理措施以及土壤pH、温度等环境因子均会影响农田土壤N₂O产生和排放。本文系统论述了土壤N₂O产生的各主要途径,并综述了氮源、碳源、水分含量、氧气含量、土壤pH和温度以及其他调控因子对N₂O排放的影响,旨在阐明各过程对N₂O排放的产生机制及主要环境因子的影响,以期为后续研究提供参考和理论依据。农田土壤硝化过程本身对N₂O排放的直接贡献较小,N₂O产生的主要来源是包含硝化细菌的反硝化、硝化–反硝化耦合作用在内的生物反硝化过程。真菌反硝化和化学反硝化在酸性土壤以及硝酸异化还原成铵过程在高有机质和厌氧土壤环境中对N₂O排放具有重要作用。未来研究可从农田土壤N₂O的产生和消耗机制、降低N₂O/N₂产物比、N₂O的还原过程及相关影响因素进行深入研究。此外,利用新技术方法,探究土壤物理、化学和生物学因素对氮素转化过程的影响,重点关注N₂O峰值排放及相关联微生物的响应,并构建土壤氮素平衡和N₂O排放模型,可进一步加深对农田土壤N₂O排放机制和影响因素的理解。     

Effects of different organic fertilizers on nitrous oxide and methane emissions from double-cropping rice fields

Rice fields are a major source of greenhouse gases,such as nitrous oxide (N₂O) and methane (CH₄).Organic fertilizers may potentially replace inorganic fertilizers to meet the nitrogen requirement for rice growth;however,the simultaneous effects of organic fertilizers on N₂O and CH₄emissions and crop yield in paddy fields remain poorly understood and quantified.In this study,experimental plots were established in conventional double-cropping paddy field...     

Modelling soil compaction impacts on nitrous oxide emissions in arable fields

Nitrous oxide (N₂O) emissions comprise the major share of agriculture's contribution to greenhouse gases; however, our understanding of what is actually happening in the field remains incomplete, especially concerning the multiple interactions between agricultural practices and N₂O emissions. Soil compaction induces major changes in the soil structure and the key variables controlling N₂O emissions. Our objective was to analyse the ability of a process‐based model (Nitrous Oxide Emissions (NOE)) to simulate the impact of soil compaction on N₂O emission kinetics obtained from field experiments. We used automatic chambers to continuously monitor N₂O and CO₂ emissions on uncompacted and compacted areas in sugar beet fields during 2 years. Soil compaction led to smaller CO₂ emissions and larger N₂O emissions by inducing anoxic conditions favourable for denitrification. Cumulative N₂O emissions during the crop cycles were 944 and 977 g N ha⁻¹ in uncompacted plots and 1448 and 1382 g N ha⁻¹ in compacted plots in 2007 and 2008, respectively. The NOE model ( Hénault et al., 2005 ) simulated 106 and 138 g N₂O‐N ha⁻¹ in uncompacted plots and 1550 and 650 g N₂O‐N ha⁻¹ in compacted plots in 2007 and 2008, respectively, markedly under‐estimating the nitrification rates and associated N₂O emissions. We modified the model on the basis of published results in order to better simulate nitrification and account for varying N₂O fractions of total end‐products in response to varying soil water and nitrate contents. The modified model (NOE2) better predicted nitrification rates and N₂O emissions following fertilizer addition. Using a fine vertical separation of soil layers of configurable, but constant, thickness (1 cm) also improved the simulations. NOE2 predicted 428 and 416 g N‐N₂O ha⁻¹ in uncompacted plots and 1559 and 1032 g N‐ N₂O ha⁻¹ in compacted plots in 2007 and 2008, respectively. These results show that a simple process‐based model can be used to predict successfully the post‐fertilizer addition kinetics of N₂O emissions and the impact of soil compaction on these emissions. However, large emissions later on during the cropping cycle were not captured by the model, emphasizing the need for further research.     

灌溉方式和秸秆还田对设施番茄田CO2排放的影响

中国北方下沉式设施菜田表层土壤缺失,以及高温高湿的环境条件,导致耕层土壤有机质含量低、矿化快。如何减缓土壤有机质矿化,是该文所关注的焦点问题。该研究采用二因素试验设计,主因素为灌溉方式（传统畦灌施肥、滴灌施肥）,副因素为秸秆（含C量为0、3 500 kg/hm2）。测定了48 h内每3 h的CO2排放通量,以及全生育期CO2日排放通量、土壤温度。结果表明：1）08:00−09:00测定的土壤CO2排放通量与CO2日均排放通量不存在显著差异,二者呈极显著线性正相关关系,其决定系数为0.987;而其他时段测定值与日均值均存在显著差异。2）与传统畦灌相比,无论是否添加秸秆,滴灌处理均显著降低了CO2累积排放量。3）CO2排放高峰出现在定植后8～15 d,随后逐渐降低并趋于平稳;定植后40 d内能检测到处理间CO2日排放通量的差异,此后处理间差异不显著。4）CO2累积排放通量和土壤积温呈显著正相关关系。综上所述,滴灌施肥栽培体系可显著降低土壤CO2排放量,有利于设施菜田土壤有机质的积累。     

中国农业温室气体排放量测算及影响因素研究

农业生产过程所产生的温室气体在全球生产活动温室气体排放总量中占有很大比例,因此对农业温室气体的排放量进行测算并分析其影响因素,对实现农业节能减排有重要意义。本文基于1993―2011年中国农业生产的相关统计数据,借鉴前人关于农业生产中各种温室气体排放源排放系数的研究成果,测算了中国农业生产过程中的CH4、N2O和CO2排放量,并分析了影响因素。结果表明,CH4排放量基本平稳波动不大,N2O排放量从1993年的93.21万t波动增加到2011年的120.51万t,农业生产资料CO2排放量由15 626.98万t增加到31 258.10万t。种植业CO2排放主要分为土壤排放和生产资料排放,土壤CO2排放与大气温度、土壤温度、地表温度和土壤水分有关,生产资料CO2排放主要是由化肥和农药造成的;种植业CH4、N2O排放原因较为复杂,还有待进一步研究;动物肠道发酵CH4、N2O排放的影响因素主要取决于动物种类、饲料特性、饲养方式和粪便管理方式等。     

Factors influencing nitrous oxide and methane emissions from minerotrophic fens in northeast Germany

 At two field sites representing northeastern German minerotrophic fens (Rhin-Havelluch, a shallow peat site; Gumnitz, a partially drained peat site) the influence of different factors (N fertilization, groundwater table, temperature) on N₂O and CH₄ emissions was investigated. The degraded fens were sources or sinks of the radiatively active trace gases investigated. The gas fluxes measured were much higher than those found in other terrestrical ecosystems such as forests. Lowering the groundwater table increased the release of N₂O and the oxidation of CH₄. High CH₄ emission rates occurred when the groundwater tables and soil temperatures were high (>12  °C). N fertilization stimulated the release of N₂O only when application rates were very high (480 kg N ha^–1). A moderate N supply (60 or 120 kg N ha^–1) hardly increased the release of N₂O in spite of high soluble soil NO₃ ^– contents. Received: 31 October 1997     

加气灌溉温室番茄地土壤N2O排放特征

加气灌溉引起的土壤中氧气含量改变势必会影响N_2O的产生和排放。为了揭示加气灌溉对秋冬茬温室番茄地土壤N_2O排放的影响,2014年采用静态箱-气相色谱法对加气灌溉土壤N_2O排放进行原位观测,研究秋冬茬温室番茄地土壤N_2O排放对加气灌溉的动态响应。试验采用灌水量(充分灌溉、亏缺灌溉)和加气(加气、不加气)的双因素设计,设置4个处理,分别为加气亏缺灌溉(A1)、不加气亏缺灌溉(CK1)、加气充分灌溉(A2)和不加气充分灌溉(CK2)。结果表明:不同加气灌溉模式下土壤N_2O排放均主要集中在番茄果实膨大期,其他时期排放水平较低。加气和充分供水处理均增加了番茄整个生育期的土壤N_2O排放量,以A2处理最大(120.34 mg/m2),分别是A1和CK1处理的1.89和4.21倍(P0.01),而与CK2处理差异性不显著(P=0.078)。此外,不同灌水水平不加气处理,除N_2O排放主峰值点外,N_2O排放通量与土壤充水孔隙率(water-filled pore space,WFPS)存在指数正相关关系(P0.05),WFPS在46.0%~52.1%时观测到N_2O剧烈释放。可见,加气灌溉增加了温室番茄地土壤N_2O排放,且在亏缺灌溉条件下,加气灌溉对温室番茄地土壤N_2O排放的影响显著。研究结果为评估加气灌溉技术的农田生态效应及设施菜地温室气体减排提供参考。     

水肥气耦合滴灌番茄地土壤N2O排放特征及影响因素分析

为了解水肥气耦合滴灌下不同水肥气调控措施对土壤N_2O排放的影响,该研究设置施氮量(低氮和常氮)、掺气量(不掺气和循环曝气处理)和灌水量(低湿度和高湿度处理)3因素2水平完全随机试验,通过静态箱-气相色谱法、q PCR技术和结构方程模型,系统研究了不同水肥气组合方案下温室番茄地土壤N_2O排放特征及其与相关影响因素之间的关系。结果表明,水肥气耦合滴灌下N_2O排放峰值出现在施氮后2 d内,其余时期N_2O排放通量较低且变幅较小。施氮量、掺气量和灌水量的增加可增加土壤N_2O排放通量和排放总量。其中,高湿度条件下N_2O排放总量较低湿度平均增加了30.14%,曝气条件下N_2O排放总量较对照平均增加了35.16%,常氮条件下N_2O排放总量较低氮平均增加了33.83%。施氮量、掺气量和灌水量的增加可提高温室番茄的产量和氮肥偏生产力。土壤NH4+-N和NO3--N含量对N_2O排放的总效应为0.60和0.79,是影响水肥气耦合滴灌下土壤N_2O排放的主导因子。综合考虑作物产量、N_2O排放总量和氮肥偏生产力,常氮曝气低湿度处理是适宜的水肥气耦合滴灌方案。     

氮肥与生物炭施用对稻麦轮作系统甲烷和氧化亚氮排放的影响

【目的】以我国稻麦轮作系统为对象,研究氮肥和小麦秸秆生物炭联合施用对CH4和N2O排放规律的影响;结合小麦和水稻总产量进而评估对该生态系统综合温室效应(GWP)和温室气体强度(GHGI)的影响,为生物炭在减缓全球气候变化及农业生产中的推广应用提供科学依据。【方法】生物炭通过小麦秸秆在300 500℃条件下炭化获得。田间试验于2012年11月至2013年10月进行,为稻麦轮作体系。采用静态暗箱—气相色谱法观测CH4和N2O排放通量;试验共设置不施氮肥不施生物炭(N0B0)、不施氮肥施20 t/hm2生物炭(N0B1)、施氮肥不施生物炭(N1B0)、氮肥与20 t/hm2生物炭配施(N1B1)、氮肥与40 t/hm2生物炭配施(N1B2)等5个处理,各处理3次重复。【结果】单施氮肥(N1B0)与不施氮肥(N0B0)处理相比,增加了稻麦轮作产量82.8%,增加了CH4排放0.6倍,增加了N2O排放5.5倍。单施生物炭(N0B1)与不施生物炭(N0B0)处理相比,显著增产25.4%,却不能减少CH4和N2O的排放。在施氮的同时,配施20 t/hm2生物炭与单施氮肥处理相比,显著增加稻麦轮作产量21.6%,小麦和水稻总产量也比配施40 t/hm2生物炭处理高;配施40 t/hm2生物炭与单施氮肥处理相比,显著降低稻麦轮作系统CH4排放11.3%和N2O排放20.9%,CH4和N2O排放量也比配施20 t/hm2生物炭的排放量低。随着生物炭配施量的增加,CH4和N2O减排效果更明显。单施生物炭并不能有效地减少GWP,但却可以显著增加作物产量,从而减小GHGI。对N0B0、N0B1、N1B0、N1B1四个处理进行双因素方差分析发现,氮肥和生物炭在CH4和N2O排放、作物产量、GWP和GHGI方面都不存在明显的交互作用。各处理在100 a时间尺度上总GWP由大到小的顺序为N1B0N1B1N1B2N0B0N0B1,GHGI值由大到小的顺序则为N1B0N1B1N0B0N1B2N0B1。单施生物炭与配施生物炭都能降低稻麦轮作系统的GWP和GHGI,配施40 t/hm2生物炭处理降低效果更好。【结论】稻田麦季施用不同水平生物炭都能在保产或增产的同时,降低稻麦轮作系统CH4和N2O的排放及GWP和GHGI。在当前稻麦轮作系统中,与20 t/hm2的生物炭施用量相比,40 t/hm2的生物炭施用量显著降低GWP,但增产效果不明显,因此二者GHGI相当,需要根据温室效应与作物产量权衡选择生物炭实际施用量。     

Effects of application of lime nitrogen and dicyandiamide on nitrous oxide emissions from green tea fields

Abstract

The aim of this study was to assess the mitigating effects of lime nitrogen (calcium cyanamide) and dicyandiamide (DCD) application on nitrous oxide (N₂O) emissions from fields of green tea [Camellia sinensis (L.) Kuntze]. The study was conducted in experimental tea fields in which the fertilizer application rate was 544 kg nitrogen (N) ha^?1 yr^?1 for 2 years. The mean cumulative N₂O flux from the soil between the canopies of tea plants for 2 years was 7.1 ± 0.9 kg N ha^?1 yr^?1 in control plots. The cumulative N₂O flux in the plots supplemented with lime nitrogen was 3.5 ± 0.1 kgN ha^?1, approximately 51% lower than that in control plots. This reduction was due to the inhibition of nitrification by DCD, which was produced from the lime nitrogen. In addition, the increase in soil pH by lime in the lime nitrogen may also be another reason for the decreased N₂O emissions from soil in LN plots. Meanwhile, the cumulative N₂O flux in DCD plots was not significantly different from that in control plots. The seasonal variability in N₂O emissions in DCD plots differed from that in control plots and application of DCD sometimes increased N₂O emissions from tea field soil. The nitrification inhibition effect of lime nitrogen and DCD helped to delay nitrification of ammonium-nitrogen (NH₄⁺-N), leading to high NH₄⁺-N concentrations and a high ratio of NH₄⁺-N /nitrate-nitrogen (NO₃^–-N) in the soil. The inhibitors delayed the formation of NO₃^–-N in soil. N uptake by tea plants was almost the same among all three treatments.     

灌水下限与毛管埋深对温室番茄生长的影响

为探明番茄根系生长与水分分布之间的互反馈机制,通过日光温室地下滴灌试验,设置了4种毛管埋深(0 cm、10 cm、20 cm和30 cm)和3种灌水下限(保持土壤含水量为50%、60%和75%田间持水量),研究了不同灌水下限与毛管埋深对番茄根系生长及干物质分配的影响。研究结果表明,轻度、中轻度水分亏缺(灌水下限为75%和60%田间持水量)时,毛管埋深对番茄耗水量有显著影响,10~20 cm毛管埋深提高番茄耗水量。毛管埋深增加会减少0~20 cm土层根系分布,促进20~60 cm土层根系生长;毛管埋深对0~10 cm、20~30 cm、30~40 cm土层根系生长影响显著,对50~60 cm土层根系生长无显著影响。灌水下限对细根(d1 mm)、粗根(d1mm)的根长与根表面积影响显著,毛管埋深对细根的根长与根表面积有显著影响;轻度水分亏缺及20 cm毛管埋深有利于细根根长和根表面积生长,减少粗根比例。本研究结果表明,轻度水分亏缺及毛管埋深为20 cm更有利于全株干物质积累,灌水下限为75%田间持水量能够增加根系干物质分配比例,而20 cm毛管埋深则能促进干物质向茎叶转移且减少根系干物质的分配比例。     

The effect of soil texture and soil drainage on emissions of nitric oxide and nitrous oxide

Abstract. Agricultural soils are important sources of the tropospheric ozone precursor NO and the greenhouse gas N₂O. Emissions are controlled primarily by parameters that vary the soil mineral N supply, temperature and soil aeration. In this field experiment, the importance of soil physical properties on emissions of NO and N₂O are identified. Fluxes were measured from 13 soils which belonged to 11 different soil series, ranging from poorly drained silty clay loams to freely drained sandy loams. All soils were under the same soil management regime and crop type (winter barley) and in the same maritime climate zone. Despite this, emissions of NO and N₂O ranged over two orders of magnitude on all three measurement occasions, in spring before and after fertilizer application, and in autumn after harvest. NO emissions ranged from 0.3 to 215 μg NO-N m^–2 h^–1, with maximum emissions always from the most sandy, freely drained soil. Nitrous oxide emissions ranged from 0 to 193 μg N₂O-N m^–2 h^–1. Seasonal shifts in soil aeration caused maximum N₂O emissions to switch from freely drained sandy soils in spring to imperfectly drained soils with high clay contents in autumn. Although effects of soil type on emissions were not consistent, N₂O emission was best related to a combination of bulk density and clay content and the NO/N₂O ratio decreased logarithmically with increasing water filled pore space.     

不同水稻、小麦品种对N2O排放的影响

Plant species of cropping systems may affect nitrous oxide (N2O) emissions. A field experiment was conducted to investigate dynamics of N2O emissions from rice-wheat fields from December 2006 to June 2007 and the relationship between soil and plant parameters with N2O emissions. The results indicated that N2O emissions from different wheat varieties ranged from 12 to 291 μg N2O-N m-2 h-1 and seasonal N2O emissions ranged from 312 to 385 mg N2O-N m-2. In the rice season, it was from 11 to 154 μg N2O-N m-2 h-1 with seasonal N2O emission of 190--216 mg N2O-N m-2. The seasonal integrated flux of N2O differed significantly among wheat and rice varieties. The wheat variety HUW 234 and rice variety Joymoti showed higher seasonal N2O emissions. In the wheat season, N2O emissions correlated with soil organic carbon (SOC), soil NO3--N, soil temperature, shoot dry weight, and root dry weight. Among the variables assessed, soil temperature followed by SOC and soil NO3--N were considered as the important variables influencing N2O emission. N2O emission in the rice season was significantly correlated with SOC, soil NO3--N, soil temperature, leaf area, shoot dry weight, and root dry weight. The main driving forces influencing N2O emission in the rice season were soil NO3--N, leaf area, and SOC.     

Decreased nitrous oxide emissions associated with functional microbial genes under bio-organic fertilizer application in vegetable fields

Bio-organic fertilizers enriched with plant growth-promoting microbes(PGPMs)have been widely used in crop fields to promote plant growth and maintain soil microbiome functions.However,their potential effects on N₂O emissions are of increasing concern.In this study,an in situ measurement experiment was conducted to investigate the effect of organic fertilizer containing Trichoderma guizhouense(a plant growth-promoting fungus)on soil N₂O emissions from a greenhouse vegetable field.The following four treatments were used:no fertilizer(control),chemical fertilizer(NPK),organic fertilizer derived from cattle manure(O),and organic fertilizer containing T.guizhouense(O+T,referring to bio-organic fertilizer).The abundances of soil N cycling-related functional genes(amoA)from ammonium-oxidizing bacteria(AOB)and archaea(AOA),as well as nirS,nirK,and nosZ,were simultaneously determined using quantitative PCR(qPCR).Compared to the NPK plot,seasonal total N₂O emissions decreased by 11.7%and 18.7%in the O and O+T plots,respectively,which was attributed to lower NH₄⁺-N content and AOB amoA abundance in the O and O+T plots.The nosZ abundance was significantly greater in the O+T plot,whilst the AOB amoA abundance was significantly lower in the O+T plot than in the O plot.Relative to the organic fertilizer,bio-organic fertilizer application tended to decrease N₂O emissions by 7.9%and enhanced vegetable yield,resulting in a significant decrease in yield-scaled N₂O emissions.Overall,the results of this study suggested that,compared to organic and chemical fertilizers,bio-organic fertilizers containing PGPMs could benefit crop yield and mitigate N₂O emissions in vegetable fields.     

水肥管理对鄱阳湖流域稻田温室气体排放的影响

为探明水肥管理模式对稻田温室气体（CH4,CO2和N2O）的影响规律,以鄱阳湖流域赣抚平原灌区稻田为研究对象,考虑间歇灌溉（W1）和淹灌（W0）2种灌溉模式,不施氮（N0）、减量施氮（N1,135 kg/hm2）和常规施氮（N2,180 kg/hm2）3种施氮水平,采用静态箱-气相色谱法测定气体排放量,结合产量计算温室气体排放强度。结果表明：稻田CH4和CO2排放通量全天内表现为单峰模式,CH4日排放峰值在14:00-15:00,CO2排放峰值提前约1～2 h,而N2O排放通量全天内则表现为上午、傍晚和深夜的三峰模式。08:00-11:00内3种气体校正系数和综合值均比较接近1,是进行田间观测的最佳时段。稻田CH4排放通量在生育前期迅速增长达到峰值,中后期相对平缓并伴有1～2个小峰值。间歇灌溉CH4排放通量较少。不同水肥处理下CO2排放的峰值出现次数一致,主要在分蘖前期、乳熟期和黄熟期。2种灌溉模式的CO2排放规律一致,但间歇灌溉下CO2排放量更多。稻田N2O的排放整体水平呈现较低状态,各处理的N2O排放峰值出现在抽穗开花期末。稻田温室气体排放引起的增温潜势受灌溉模式的影响极显著。与W0相比,W1在N0、N1、N2水平下分别降低增温潜势 36.1%、33.9%和23.2%（P<0.05）。地温和气温是重要的环境影响因子,CH4和CO2对地温的敏感性高于气温,9月典型日的温度敏感系数更高。W1N1处理的温室气体排放强度最低,从减排增产角度为鄱阳湖流域推荐的稻田水肥管理模式。     

The contribution of agricultural practices to nitrous oxide emissions in semi-arid Mali

The yield and flux of nitrous oxide (N₂O) emitted from continuous cereals (with and without urea), legumes/cereal in rotation and cereal/legume in rotation all with or without organic manure was monitored from January 2004 to February 2005. All treatments except continuous cereals had phosphate added. The cereal grown July–October in 2003 and 2004 was pearl millet ( Pennisetum glaucum) and the legume was a bean ( Phaseolus vulgaris ). The 10 m × 10 m plots were established in a semi-arid climate in Mali. The addition of organic manure and both inorganic fertilizers increased yield and N₂O emissions. Continuous cereals treated with both organic manure and urea emitted significantly less N₂O (882 g N/ha per year) than plots receiving no organic manure(1535 g N/ha per year). Growing N-fixing crops in rotation did not significantly increase N₂O emissions. This study supports the new practice of growing cereal and legumes in rotation as an environmentally sustainable system in semi-arid Mali.     

The effect of reduced tillage on nitrous oxide emissions of silt loam soils

The effect of reduced tillage (RT) on nitrous oxide (N₂O) emissions of soils from fields with root crops under a temperate climate was studied. Three silt loam fields under RT agriculture were compared with their respective conventional tillage (CT) field with comparable crop rotation and manure application. Undisturbed soil samples taken in September 2005 and February 2006 were incubated under laboratory conditions for 10 days. The N₂O emission of soils taken in September 2005 varied from 50 to 1,095 μg N kg⁻¹ dry soil. The N₂O emissions of soils from the RT fields taken in September 2005 were statistically (P < 0.05) higher or comparable than the N₂O emissions from their respective CT soil. The N₂O emission of soils taken in February 2006 varied from 0 to 233 μg N kg⁻¹ dry soil. The N₂O emissions of soils from the RT fields taken in February 2006 tended to be higher than the N₂O emissions from their respective CT soil. A positive and significant Pearson correlation of the N₂O–N emissions with nitrate nitrogen (NO₃ ⁻–N) content in the soil was found (P < 0.01). Leaving the straw on the field, a typical feature of RT, decreased NO₃ ⁻–N content of the soil and reduced N₂O emissions from RT soils.