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1.
Nitrous oxide emission (N2O) from applied fertilizer across the different agricultural landscapes especially those of rainfed area is extremely variable (both spatially and temporally), thus posing the greatest challenge to researchers, modelers, and policy makers to accurately predict N2O emissions. Nitrous oxide emissions from a rainfed, maize-planted, black soil (Udic Mollisols) were monitored in the Harbin State Key Agroecological Experimental Station (Harbin, Heilongjiang Province, China). The four treatments were: a bare soil amended with no N (C0) or with 225?kg?N ha?1 (CN), and maize (Zea mays L.)-planted soils fertilized with no N (P0) or with 225?kg?N ha?1 (PN). Nitrous oxide emissions significantly (P?<?0.05) increased from 141?±?5?g N2O-N?ha?1 (C0) to 570?±?33?g N2O-N?ha?1 (CN) in unplanted soil, and from 209?±?29?g N2O-N?ha?1 (P0) to 884?±?45?g N2O-N?ha?1 (PN) in planted soil. Approximately 75?% of N2O emissions were from fertilizer N applied and the emission factor (EF) of applied fertilizer N as N2O in unplanted and planted soils was 0.19 and 0.30?%, respectively. The presence of maize crop significantly (P?<?0.05) increased the N2O emission by 55?% in the N-fertilized soil but not in the N-unfertilized soil. There was a significant (P?<?0.05) interaction effect of fertilization?×?maize on N2O emissions. Nitrous oxide fluxes were significantly affected by soil moisture and soil temperature (P?<?0.05), with the temperature sensitivity of 1.73–2.24, which together explained 62–76?% of seasonal variation in N2O fluxes. Our results demonstrated that N2O emissions from rainfed arable black soils in Northeast China primarily depended on the application of fertilizer N; however, the EF of fertilizer N as N2O was low, probably due to low precipitation and soil moisture.  相似文献   

2.
施肥方式对紫色土农田生态系统N2O和NO排放的影响   总被引：1，自引：1，他引：0  
依托紫色土施肥方式与养分循环长期试验平台(2002年—),采用静态箱-气相色谱法开展紫色土冬小麦-夏玉米轮作周期(2013年10月至2014年10月)农田生态系统N_2O和NO排放的野外原位观测试验。长期施肥方式包括单施氮肥(N)、传统猪厩肥(OM)、常规氮磷钾肥(NPK)、猪厩肥配施氮磷钾肥(OMNPK)和秸秆还田配施氮磷钾肥(RSDNPK)等5种,氮肥用量相同[小麦季130 kg(N)×hm~(-2),玉米季150 kg(N)×hm~(-2)],不施肥对照(CK)用于计算排放系数,对比不同施肥方式对紫色土典型农田生态系统土壤N_2O和NO排放的影响,以期探寻紫色土农田生态系统N_2O和NO协同减排的施肥方式。结果表明,所有施肥方式下紫色土N_2O和NO排放速率波动幅度大,且均在施肥初期出现峰值;强降雨激发N_2O排放,但对NO排放无明显影响。在整个小麦-玉米轮作周期,N、OM、NPK、OMNPK和RSDNPK处理的N_2O年累积排放量分别为1.40 kg(N)×hm~(-2)、4.60 kg(N)×hm~(-2)、0.95 kg(N)×hm~(-2)、2.16kg(N)×hm~(-2)和1.41 kg(N)×hm~(-2),排放系数分别为0.41%、1.56%、0.25%、0.69%、0.42%;NO累积排放量分别为0.57 kg(N)×hm~(-2)、0.40 kg(N)×hm~(-2)、0.39 kg(N)×hm~(-2)、0.46 kg(N)×hm~(-2)和0.17 kg(N)×hm~(-2),排放系数分别为0.21%、0.15%、0.15%、0.17%、0.07%。施肥方式对紫色土N_2O和NO累积排放量具有显著影响(P0.05),与NPK处理比较,OM和OMNPK处理的N_2O排放分别增加384%和127%,同时NO排放分别增加3%和18%;RSDNPK处理的NO排放减少56%。表明长期施用猪厩肥显著增加N_2O和NO排放,而秸秆还田有效减少NO排放。研究表明,土壤温度和水分条件均显著影响小麦季N_2O和NO排放(P0.01),对玉米季N_2O和NO排放没有显著影响(P0.05),土壤无机氮含量则是在小麦-玉米轮作期N_2O和NO排放的主要限制因子(P0.01)。全量秸秆还田与化肥配合施用是紫色土农田生态系统N_2O和NO协同减排的优化施肥方式。  相似文献   

3.
有机无机肥料配合施用对设施菜田土壤N2O排放的影响   总被引：11，自引：3，他引：8  
采用静态箱气相色谱法研究了有机无机肥料配合施用对设施菜田土壤N2O排放的影响。结果表明: 1）设施芹菜和番茄施基肥后57 d（灌溉后13 d）出现土壤N2O排放通量峰值,追肥后（施肥与灌溉同步）1 d出现土壤N2O排放通量峰值; 芹菜季和番茄季施用基肥后20 d内N2O排放量分别占当季总排放量的40%65%左右,是土壤N2O主要排放期。2）施用基肥后至定植灌水前各处理土壤N2O排放量逐渐降低,灌水后N2O排放通量迅速上升。各处理土壤N2O排放通量与土壤含水量之间呈显著相关,相关系数在0.43~0.72之间。3）土壤N2O排放主要发生在番茄季,番茄生育期各处理土壤N2O总排放量是芹菜生育期的3.1倍; 各处理土壤N2O排放通量与5 cm土层温度之间总体上呈显著相关,相关系数在0.40~0.58之间。4）设施菜田大幅减施化肥的有机无机肥配合施用模式可显著降低土壤N2O排放量和肥料损失率,芹菜季和番茄季土壤N2O排放量较习惯施肥处理分别降低66.3%和85.1%,肥料损失率分别降低45.2%和74.9%。5）等氮量投入时,施用秸秆较施用猪粪可有效降低土壤N2O排放,芹菜季和番茄季分别降低43.4%和74.2%。  相似文献   

4.
施肥方式对冬小麦季紫色土N2O排放特征的影响   总被引：8，自引：2，他引：6  
利用紫色土养分循环长期定位施肥试验平台,通过静态箱-气相色谱法,于2012年11月至2013年5月,研究了单施氮肥(N)、猪厩肥(OM)、常规氮磷钾肥(NPK)、猪厩肥配施氮磷钾肥(OMNPK)、秸秆还田配施氮磷钾肥(CRNPK)及对照不施肥(NF)6种施肥方式下,紫色土冬小麦季土壤N2O的排放特征。结果表明,在相同施氮水平[130 kg(N)·hm-2]下,施肥方式对N2O排放量有显著影响(P0.05)。N、OM、NPK、OMNPK和CRNPK处理下,土壤N2O排放量[kg(N)·hm-2]分别为0.38、0.36、0.29、0.33和0.19,N2O排放系数分别为0.25%、0.23%、0.18%、0.21%和0.10%。NF的土壤N2O排放量为0.06 kg(N)·hm-2。土壤无机氮含量(NO3--N和NH4+-N)是N2O排放的主要影响因子,降雨能有效激发N2O排放。基于小麦产量评价不同施肥方式下的N2O排放,结果表明,N、OM、NPK、OMNPK和CRNPK单位小麦产量N2O的GWP值[yield-scaled GWP,kg(CO2 eq)·t-1]分别为132.57、45.70、49.07、48.92和26.41。CRNPK的小麦产量与6种施肥方式中获得最大产量的OM间没有显著差异,但显著高于其他处理。而且,CRNPK的yield-scaled GWP比紫色土地区冬小麦种植中常规施肥方式(NPK)显著减少46%,并显著低于其他4种施肥方式。可见,秸秆还田配施氮磷钾肥在保证小麦产量的同时,能有效减少因施肥引发的N2O排放,可作为紫色土地区推荐的最佳施肥措施。  相似文献   

5.
Nitrous oxide (N2O) emissions from grazed pastures constitute approximately 28% of total global anthropogenic N2O emissions. The aims of this study were to investigate the effect of inorganic N fertilizer application on fluxes of N2O, quantify the emission factors (EFs) for a sandy loam soil which is typical of large areas in Ireland and to investigate denitrification sensitivity to temperature. Nitrous oxide flux measurements from a cut and grazed pasture field for 1 year and denitrification laboratory incubation were carried out. The soil pH was 7.3 and had a mean organic C and N content at 0–20 cm of 44.1 and 4.4 g/kg dry weight, respectively. The highest observed peaks of N2O fluxes of 67 and 38.7 g N2O‐N per hectare per day were associated with times of application of inorganic N fertilizer. Annual fluxes of N2O from control and fertilized treatments were 1 and 2.4 kg N2O‐N per hectare, respectively. Approximately 63% of the annual flux was associated with N fertilizer application. Multiple regression analysis revealed that soil nitrate and the interaction between soil nitrate and soil water content were the main factors controlling N2O flux from the soil. The derived EF of 0.83% was approximately 66% of the IPCC default EF value of 1.25% as used by the Irish EPA to estimate greenhouse gases (GHGs) in Ireland. The IPCC‐revised EF value is 0.9%. A highly significant exponential regression (r2 = 0.98) was found between denitrification and incubation temperature. The calculated Q10 ranged from 4.4 to 6.2 for a temperature range of 10–25 °C and the activation energy was 47 kJ/mol. Our results show that denitrification is very sensitive to increasing temperature, suggesting that future global warming could lead to a significant increase in soil denitrification and consequently N2O fluxes from soils.  相似文献   

6.
为了明确有机无机肥料配施条件下华北旱地春玉米农田N2O周年排放规律、影响因素及其净温室效应,采用静态箱-气相色谱法和生物地球化学模型（DNDC）相结合的方法,对单施化肥（NPK）、有机无机肥料配施（50％M＋50％U）、单施有机肥（M）、对照（CK）等处理的春玉米农田N2O排放情况进行了周年监测,并对DNDC模型进行验证,利用验证后的模型定量评价了不同施肥处理的净温室效应。结果表明：不同有机无机肥料配施处理N2O放通量具有明显的季节变化规律,通量变化范围是-17．56—157．25μg·m2·h-1,在非生长季观测到明显的N2O排放峰,最大排放通量为83．85μg·m2·h-1。NPK、50％M＋50％U、M、CK处理周年累计排放量分别为1．49、1．20、0．82、0．61kgN·hm-2·a-1,非生长季排放总量分别占全年总排放量的40．6％、59．2％、61．7％和60．7％,非生长季N2O排放不容忽视;在整个周年观测期内,当土壤水分含量介于19％-37％之间时,各处理下的N2O通量同土壤含水量呈极显著正相关关系。综合考虑整个农田生态系统碳收支平衡和温室气体排放,经过DNDC模型模拟表明有机无机肥料配施同单施化肥处理相比净温室效应减少33．5％,可以达到在保持产量的基础上“减排”和“固碳”的协同效果。上述研究结果为有机无机肥料合理使用以及旱地农田“稳产、减排、固碳”相协调施肥技术的筛选提供了科学依据。  相似文献   

7.
氧化亚氮（N2O）是重要的温室气体之一。本文从施肥、灌溉、耕作、种植作物及土地用途改变等方面论述了农业活动对土壤排放氧化亚氮的影响，并总结了减排措施。  相似文献   

8.
Nitrous oxide (N2O) is a high‐impact greenhouse gas. Due to the scarcity of unmanaged forests in Central Europe, its long‐term natural background emission level is not entirely clear. We measured soil N2O emissions in an unmanaged, old‐growth beech forest in the Hainich National Park, Germany, at 15 plots over a 1‐year period. The average annual measured N2O flux rate was (0.49 ± 0.44) kg N ha–1 y–1. The N2O emissions showed background‐emission patterns with two N2O peaks. A correlation analysis shows that the distance between plots (up to 380 m) does not control flux correlations. Comparison of measured data with annual N2O flux rates obtained from a standard model (Forest‐DNDC) without site‐specific recalibration reveals that the model overestimates the actual measured N2O flux rates mainly in spring. Temporal variability of measured N2O flux was better depicted by the model at plots with high soil organic C (SOC) content. Modeled N2O flux rates were increased during freezing only when SOC was > 0.06 kg C kg–1. The results indicate that the natural background of N2O emissions may be lower than assumed by most approaches.  相似文献   

9.
Nitrous oxide (N2O) fluxes from an apple orchard soil in the semiarid Loess Plateau of China were measured using static chambers from September 2007 to September 2008. In this study, three sites were selected at distance of 2.5 m (D 2.5), 1.5 m (D 1.5), and 0.5 m (D 0.5) from the apple tree row. Nitrous oxide fluxes followed seasonal pattern, with high N2O emission rates occurring in the hot-humid summer and low rates in the cold-dry winter. Pulses of N2O emissions occurred after nitrogen fertilizer application, summer rainfall events, and during freeze-thaw cycles. Annual average N2O emission rates were the highest at D 0.5 site (48.2 ± 39.9 μg N2O m−2 h−1), the lowest at D 2.5 site (31.9 ± 18.2 μg N2O m−2 h−1), and intermediate at D1.5 site (36.8 ± 32.2 μg N2O m−2 h−1), suggesting that N2O emissions from the apple orchard soil increased when the chamber location was closer to the apple tree row. This may be due to the fertilization close to roots in hot and humid season. Over one third (37.1%) of the annual N2O emission occurred in the summer. Annual N2O emissions from the apple orchard soil averaged to 3.22 kg N2O ha−1 year−1. Annual emission factor of the apple orchard from the applied fertilizer (uncorrected for background emission) was 0.658%. This value was nearly a half (53%) of the default value provided by the Intergovernmental Panel on Climate Change for the application of synthetic fertilizers to cropland (1.25%). Therefore, the amount of N2O emissions from the semiarid apple orchard soil could be largely overestimated if no regional-specific factor is used.  相似文献   

10.
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.  相似文献   

11.
We investigated the effect of environmentally smart nitrogen (ESN) fertilizer on nitrous oxide (N2O) emissions under no-till barley (Hordeum vulgare L.) production over 3 years at three sites in Alberta, Canada. Treatments included two barley cultivars, with ESN and urea applied at 1× and 1.5× the recommended rate, and herbicide at 50% and 100% of registered in-crop rates. Cumulative N2O emissions over the growing season were low (0.11 to 1.32 kg nitrogen (N) per hectare or 0.05–0.22 g N kg?1 grain yield), and not affected by barley cultivars or herbicide rates in all nine site-years, nor by fertilizer type or rate in seven out of nine site-years. However, average N2O emissions from ESN were 15% lower (P = 0.05) than urea across all site-years. Our results suggest ESN could play a role in reducing N2O emissions, but the reduction will depend on rainfall events and crop N utilization.  相似文献   

12.
施肥方式对冬小麦—夏玉米轮作土壤N_2O排放的影响   总被引：4，自引：0，他引：4  
刘韵  柳文丽  朱波 《土壤学报》2016,53(3):735-745
氧化亚氮(N_2O)是一种重要的农田温室气体,本研究利用紫色土长期施肥试验平台,采用静态箱/气相色谱法对紫色土旱作农田冬小麦—夏玉米轮作系统的N_2O排放进行了定位观测(2012年11月至2013年9月),研究单施氮肥(N)、常规氮磷钾肥(NPK)、猪厩肥(OM)、猪厩肥配施氮磷钾肥(OMNPK)和秸秆还田配施氮磷钾肥(ICRNPK)等施肥方式对紫色土N_2O排放特征的影响;不施肥(NF)作为对照计算排放系数,以探寻紫色土地区可操作性强、环境友好的施肥方式。结果表明,所有施肥方式的N_2O排放均呈现双峰排放,峰值出现在施肥初期;玉米季N_2O排放峰值显著高于小麦季(p0.05)。在相同的施氮水平(小麦季130 kg hm~(~(-2)),玉米季150 kg hm~(~(-2)))下,施肥方式对N_2O排放和作物产量均有显著影响(p0.05)。N、OM、NPK、OMNPK和ICRNPK处理的土壤N_2O周年累积排放量分别为1.93、1.96、1.12、1.50和0.79 kg hm~(~(-2)),排放系数分别为0.62%、0.63%、0.33%、0.47%和0.21%,全年作物产量分别为4.35、11.95、8.39、9.77、10.93 t hm~(~(-2))。施用猪厩肥显著增加N_2O排放量,而秸秆还田在保证作物产量的同时显著降低N_2O排放量,可作为紫色土地区环境友好的施肥方式。土壤无机氮(NO_3~--N和NH_4~+-N)是N_2O排放的主要限制因子。因此,在施氮水平相同时,施肥方式对紫色土活性氮含量的影响导致N_2O排放差异显著,是土壤N_2O排放差异的根本原因。土壤孔隙充水率也是影响N_2O排放的重要环境因子,并且其对N_2O排放的影响存在阈值效应。  相似文献   

13.
Maize(Zea mays L.), a staple crop in the North China Plain, contributing substantially to agricultural nitrous oxide(N_2O)emissions in this region. Many studies have focused on various agricultural management measures to reduce N_2O emissions. However, few have investigated soil N_2O emissions in intercropping systems. In the current study, we investigate whether maize-soybean intercropping treatments could reduce N_2O emission rates. Two differently configured maize-soybean intercropping treatments, 2:2 intercropping(two rows of maize and two rows of soybean, 2M2S) and 2:1 intercropping(two rows of maize and one row of soybean,2M1S), and monocultured maize(M) and soybean(S) treatments were performed using a static chamber method. The results showed no distinct yield advantage for the intercropping systems. The total N_2O production from the various treatments was 0.15 ± 0.04–113.85 ± 12.75 μg m~(-2) min~(-1). The cumulative N_2O emission from the M treatment was 16.9 ± 2.3 kg ha~(-1) over the entire growing season(three and a half months), which was significantly higher(P 0.05) than that of the 2M2S and 2M1S treatments by 36.6% and 32.2%, respectively. Two applications of nitrogen(N) fertilizer(as urea) at 240 kg N ha~(-1) each induced considerable soil N_2O fluxes. Short-term N_2O emissions(within one week after each of the two N applications) accounted for 74.4%–83.3% of the total emissions. Soil moisture, temperature, and inorganic N were significantly correlated with soil N_2O emissions(R~2= 0.246–0.365, n =192, P 0.001). Soil nitrate(NO_3~-) and moisture decreased in the intercropping treatments during the growing season. These results indicate that maize-soybean intercropping can reduce soil N_2O emissions relative to monocultured maize.  相似文献   

14.
Abstract

Nitrous oxide (N2O) contributes to global climate change, and its emission from soil–crop systems depend on soil, environmental, and anthropogenic factors. Thus, we evaluated the variability of N2O emissions measured by microchambers (cross section: 184 cm2) from a groundnut–fallow–maize–fallow cropping system of the humid tropics. The crops received inorganic nitrogen (N) plus crop residues (NC), inorganic N alone as ammonium sulfate (RN), and half of the inorganic N along with crop residues and chicken manure (N1/2CM), amounting for the crop rotation to 322, 180, and 400 kg N ha?1 yr?1, respectively. The N2O fluxes during the groundnut–maize crop rotation were log‐normally distributed, and the frequency distributions were positively skewed. Daytime changes in N2O fluxes were inconsistent, and the 50% of total N2O emission during the 12 h measurement periods was attained earlier under maize (～11∶00 h) than groundnut covers (～13∶00 h). Spatial variability in each treatment with eight gas chambers was large but smaller during the cropping periods than the fallow, indicating masking efficiency of crop covers for the soil heterogeneity that was accelerated presumably by antecedent climatic variables. The temporal variability of N2O emissions was also large (coefficients of variation, CV, ranged from 60 to 81%), involving both input differences between treatments and measurement periods. As such, the relative deviation from the annual mean of total N2O emission was high during the period after a large N application with a maximum of +480%, due to addition of chicken manure. The seasonal contribution of summer and monsoon to N2O emissions was insignificant. However, intensive rainfall negatively (?0.65**) and the amount of added N from either source positively (0.83***) correlated with the integrated N2O emissions, and those were exponential. Results suggest that around noon (12∶00 h) gas collection could represent well the daily N2O fluxes, increasing the number or size of the gas chambers could minimize the large variability, and mainly the rainfall and N inputs regulated its emissions in the humid tropics of Malaysia.  相似文献   

15.
A high soil nitrogen (N) content in irrigated areas quite often results in environmental problems. Improving the management practices of intensive agriculture can mitigate greenhouse gas (GHG) emissions. This study compared the effect of maize stover incorporation or removal together with different mineral N fertilizer rates (0, 200 and 300 kg N ha?1) on the emission of nitrous oxide (N2O) and carbon dioxide (CO2) on a sprinkler-irrigated maize (Zea mays L.). The trail was conducted in the Ebro Valley (NE Spain) in a high nitrate-N soil (i.e. 200 g NO3–N kg?1). Nitrous oxide and CO2 emissions were sampled weekly using a semi-static closed chamber and quantified using the photoacoustic technique in 2011 and 2012. Applying sidedress N fertilizer tended to increase N2O emissions whereas stover incorporation did not have any clear effect. Nitrification was probably the main process leading to N2O. Denitrification was limited by the low soil moisture content (WFPS <?54%), due to an adequate irrigation management. Emissions ranged from ??0.11 to 0.36% of the N applied, below the IPCC (2007) values. Nitrogen fertilization tended to reduce CO2 emission, but only in 2011. Stover incorporation increased CO2 emission. Nitrogen use efficiency decreased with increasing mineral fertilizer supply. The application of N in high N soils of the Ebro Valley is not necessary until the soil restores a normal mineral N content, regardless of stover management. This will combine productivity with keeping N2O and CO2 emissions under control provided irrigation is adequately managed. Testing soil NO3 ?–N contents before fertilizing would improve N fertilizer recommendations.  相似文献   

16.
In this study emissions of N2O from arable soils are summarized using data from long‐term N2O monitoring experiments. The field experiments were conducted at six sites in Germany between 1992 and 1997. The annual N‐application rate ranged from 0 to 350 kg N ha—1. Mineral and organic N‐fertilizer applications were temporarily split adapted to the growth stage of each crop. N‐fertilizer input and N‐yield by the crops were used to calculate the In/Out‐balance. The closed chamber technique was applied to monitor the N2O fluxes from soil into the atmosphere. If possible, plants were included in the covers. Annual N2O emission values were based on flux rate measurements of an entire year. The annual N2O losses ranged from 0.53 to 16.78 kg N2O‐N ha—1 with higher N2O emissions from organically fertilized plots as compared to minerally fertilized plots. Approximately 50% of the total annual emissions occurred during winter. No significant relationship between annual N2O emissions and the respective N‐fertilization rate was found. This was attributed to site‐ and crop‐specific effects on N2O emission. The calculation of the N2O emission per unit N‐yield from winter cereal plots indicates that the site effect on N2O emission is more important than the effect of N‐fertilization. From unfertilized soils at the sites Braunschweig and Timmerlah a N‐yield of 60.0 kg N ha—1 a—1 and N2O emissions of 2 kg N ha—1 a—1 were measured. This high background emission was assigned to the amount and turnover of soil organic matter. For a crop rotation at the sites Braunschweig and Timmerlah the N In/Out‐balance over a period of four years was identified as a suitable predictor of N2O emissions. This parameter characterizes the efficiency of N‐fertilization for crop production and allows for N‐mineralization from the soil.  相似文献   

17.
Agricultural soils are the main anthropogenic source of nitrous oxide (N2O), largely because of nitrogen (N) fertilizer use. Commonly, N2O emissions are expressed as a function of N application rate. This suggests that smaller fertilizer applications always lead to smaller N2O emissions. Here we argue that, because of global demand for agricultural products, agronomic conditions should be included when assessing N2O emissions. Expressing N2O emissions in relation to crop productivity (expressed as above‐ground N uptake: ‘yield‐scaled N2O emissions') can express the N2O efficiency of a cropping system. We show how conventional relationships between N application rate, N uptake and N2O emissions can result in minimal yield‐scaled N2O emissions at intermediate fertilizer‐N rates. Key findings of a meta‐analysis on yield‐scaled N2O emissions by non‐leguminous annual crops (19 independent studies and 147 data points) revealed that yield‐scaled N2O emissions were smallest (8.4 g N2O‐N kg−1N uptake) at application rates of approximately 180–190 kg N ha−1 and increased sharply after that (26.8 g N2O‐N kg−1 N uptake at 301 kg N ha−1). If the above‐ground N surplus was equal to or smaller than zero, yield‐scaled N2O emissions remained stable and relatively small. At an N surplus of 90 kg N ha−1 yield‐scaled emissions increased threefold. Furthermore, a negative relation between N use efficiency and yield‐scaled N2O emissions was found. Therefore, we argue that agricultural management practices to reduce N2O emissions should focus on optimizing fertilizer‐N use efficiency under median rates of N input, rather than on minimizing N application rates.  相似文献   

18.
Grain legume production with rhizobial inoculation has drawn attention not only because of the economic value of nitrogen (N) fixation by grain legumes, but also because of the concern that N2 fixation by grain legumes may enhance emissions of nitrous oxide (N2O), a powerful greenhouse gas. However, the relationship between N2O emissions and biological N2 fixation by grain legumes is not well understood. The objective of this study was to quantify N2O emissions associated with N2 fixation by grain legumes as affected by wetting/drying cycles and crop residues. Two grain legumes, lentil (Lens esculenta Moench) and pea (Pisum sativum L.), either inoculated with two Rhizobium leguminosarum biovar viciae strains, 99A1 and RGP2, respectively, or fertilized with 15N-labeled fertilizer were grown in a controlled environment under three wetting/drying cycles. Profile N2O concentrations and surface N2O emissions were measured from the soil–plant systems, which were compared with those from a cereal, spring wheat (Triticum aestivum L. ac. Barrie). After harvest, crop residues were incorporated into soils that were seeded to spring wheat to evaluate the effect of crop residues on N2O emissions. Results indicated that: (1) inoculating grain legumes with non-denitrifying rhizobia did not enhance N2O emissions and the presence of grain legumes did not increase N2O emissions compared with the cereal crop, and (2) profile N2O accumulation and surface emissions were not related to the type of crop residues added to the soil, but related to the residual N applied previously as N fertilizer. This suggests that N2O emissions are not directly related to biological N2 fixation by grain legumes, and on a short time scale, N rich residues of N2-fixing crops have a limited impact on N2O emissions compared with N fertilization.  相似文献   

19.
Agricultural peat soils are important sources of nitrous oxide (N2O). Emissions of N2O were measured from field plots of grass, barley, potatoes and fallow on a peat field in northern Finland during 2000–2002 and in southern Finland in 1999–2002. In the north the mean annual fluxes of N2O (with their standard errors) during 2 years were 4.0 (±1.2), 13 (±3.0) and 4.4 (±0.8) kg N ha?1 from the plots of grass, barley and fallow, respectively. In the north there were no significant thaw periods in the middle of winter. As a result, the thawing in the spring did not induce especially large N2O emissions. Emissions of N2O were larger in the south than in the north. In the southern peat field the mean annual fluxes during 3 years were 7.3 (±1.2), 15 (±2.6), 10 (±1.9) and 25 (±6.9) kg N2O‐N ha?1 for grass, barley, potato and fallow plots, respectively. Here, the largest single episodes of emission occurred during the spring thaw each year, following winter thaw events. An emission factor of 10.4 kg N2O‐N ha?1 year?1 for the N2O emission from the decomposition of the peat results from these data if the effect of fertilization according to the IPCC default emission factor is omitted. The direct effect of adding N as fertilizer on N2O emissions was of minor importance. On average, 52% of the annual N2O flux entered the atmosphere outside the cropping season (October–April) in the north and 55% in the south. The larger N2O fluxes from the peat soil in the south might be due to the more humified status of the peat, more rapid mineralization and weather with more cycles of freezing and thawing in the winter.  相似文献   

20.
For a long time, farmers in the red soil region of southern China have returned crop residues to the soil, but how various crop residues influence nitrous oxide (N2O) emissions is not well understood. We compared the influence of returning different crop residues [rapeseed cake (RC), maize straw, rice straw and wheat straw (WS)] in combination with different levels of nitrogen (N) fertilizer (nil, low and high) on red soil N2O emissions. Results confirmed the inverse relationship between cumulative N2O emissions and residue C:N ratio in red soil under different levels of N fertilizer. However, N‐fertilizer application did not significantly influence N2O emissions in the WS (which had the highest C:N ratio) and corresponding control treatments, while it enhanced N2O emissions in the RC (which had the lowest C:N ratio) treatment and displayed significantly higher cumulative N2O emissions with low N fertilizer application. This phenomenon may be attributed to the poor nutrient content in red soil, which leads to ‘Liebig's Law of the Minimum’ on available C. N fertilizer application provided sufficient available N, while the readily available C, which was mainly dependent on the degradability of the residue, became the crucial factor influencing N2O emissions. Additional experiments, which showed that the addition of glucose and sucrose could increase N2O emissions when N () was sufficient, confirmed this hypothesis. Thus, to reduce N2O emissions when returning residues to red soil, we suggest that both the residue C:N ratio and the quality should be considered when deciding whether to apply N fertilizer.  相似文献   

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