有机、无机氮肥施用对苜蓿产量、土壤硝态氮和温室气体排放的影响

2012年5月—2014年6月,采用田间小区试验方法,研究了不同氮肥管理对N₂O与CH₄的排放、土壤硝态氮含量以及苜蓿干草产量的影响.试验共设5个处理:对照(CK)、单施尿素处理(100 kg N·hm^-2, CF)、尿素(100 kg N·hm^-2)与腐熟牛粪(60 kg N·hm^-2)混施处理(DM₁)、尿素(100 kg N·hm^-2)与沼液(60 kg N·hm^-2)混施处理(DT)及减量尿素(40 kg N·hm^-2)与牛粪(60 kg N·hm^-2)混施处理(DM₂).结果表明: 与CK相比,CF、DM₁、DT和DM₂处理苜蓿干草产量分别增加44.2%、38.9%、56.3%和30.6%,N₂O排放分别比对照增加52.2%、89.1%、133.7%和59.4%,但各施肥处理对甲烷吸收表现出不同程度的抑制作用.苜蓿生产中,尿素和牛粪处理N₂O-N排放与肥料氮素投入量比值(排放系数)为0.25%～0.28%,而沼液处理N₂O-N排放系数为0.64%,显著高于前者.苜蓿生产中,施用化肥或有机无机混施均能显著增加苜蓿干物质产量,土壤硝态氮深层淋洗风险较小,但增加了CO_2-equivalent净排放量.     

Infield greenhouse gas emissions from sugarcane soils in Brazil: effects from synthetic and organic fertilizer application and crop trash accumulation

Bioethanol from sugarcane is becoming an increasingly important alternative energy source worldwide as it is considered to be both economically and environmentally sustainable. Besides being produced from a tropical perennial grass with high photosynthetic efficiency, sugarcane ethanol is commonly associated with low N fertilizer use because sugarcane from Brazil, the world's largest sugarcane producer, has a low N demand. In recent years, several models have predicted that the use of sugarcane ethanol in replacement to fossil fuel could lead to high greenhouse gas (GHG) emission savings. However, empirical data that can be used to validate model predictions and estimates from indirect methodologies are scarce, especially with regard to emissions associated with different fertilization methods and agricultural management practices commonly used in sugarcane agriculture in Brazil. In this study, we provide in situ data on emissions of three GHG (CO₂, N₂O, and CH₄) from sugarcane soils in Brazil and assess how they vary with fertilization methods and management practices. We measured emissions during the two main phases of the sugarcane crop cycle (plant and ratoon cane), which include different fertilization methods and field conditions. Our results show that N₂O and CO₂ emissions in plant cane varied significantly depending on the fertilization method and that waste products from ethanol production used as organic fertilizers with mineral fertilizer, as it is the common practice in Brazil, increase emission rates significantly. Cumulatively, the highest emissions were observed for ratoon cane treated with vinasse (liquid waste from ethanol production) especially as the amount of crop trash on the soil surface increased. Emissions of CO₂ and N₂O were 6.9 kg ha^?1 yr^?1 and 7.5 kg ha^?1 yr^?1, respectively, totaling about 3000 kg in CO₂ equivalent ha^?1 yr^?1.     

Effect of improved nitrogen management on greenhouse gas emissions from intensive dairy systems in the Netherlands

Dairy systems in Europe contribute to the emissions of the greenhouse gases (GHGs) nitrous oxide (N₂O), methane (CH₄) and carbon dioxide (CO₂). In this paper, the effects of improved nitrogen (N) management on GHG emissions from Dutch dairy farms are determined. The GHG emissions are calculated using the panel on climate change (IPCC) methodology for the Netherlands, an updated and refined IPCC methodology, and a full accounting approach. The changes in dairy farming over the last 20 years, and the consequences for N management are described using detailed farm‐level data, collected in 1985, 1997 and 2002. The selected years represent distinct stages in the implementation of N policies. The changes in N management have reduced the GHG emissions. A reduction of the N surplus per kilogram milk with 1 g N reduced the GHG emissions per kilogram milk with approximately 29 g CO₂‐equivalents. The reduction of the N surpluses was mainly brought about by reduced fertilizer use and reduced grazing time. The use of updated and refined emission factors resulted in higher CH₄ emissions and lower N₂O emissions. On average, the overall emission was 36% higher with the refined method. Full accounting, including all direct and indirect emissions of CH₄, N₂O and CO₂, increased the emission with 36% compared with the refined IPCC methodology. We conclude that the N surplus at farm level is a useful indicator of GHG emissions. A full accounting system as presented in this study may effectively enable farmers to address the issue of emissions of GHGs in their operational management decisions. Both approaches serve their own specific objectives: full accounting at the farm level to explore mitigation options, and the IPCC methods to report changes in GHG emissions at the national level.     

Impacts of natural factors and farming practices on greenhouse gas emissions in the North China Plain: A meta‐analysis

Requirements for mitigation of the continued increase in greenhouse gas (GHG ) emissions are much needed for the North China Plain (NCP ). We conducted a meta‐analysis of 76 published studies of 24 sites in the NCP to examine the effects of natural conditions and farming practices on GHG emissions in that region. We found that N₂O was the main component of the area‐scaled total GHG balance, and the CH ₄ contribution was <5%. Precipitation, temperature, soil pH , and texture had no significant impacts on annual GHG emissions, because of limited variation of these factors in the NCP . The N₂O emissions increased exponentially with mineral fertilizer N application rate, with y  =  0.2389e^0.0058x for wheat season and y  =  0.365e^0.0071x for maize season. Emission factors were estimated at 0.37% for wheat and 0.90% for maize at conventional fertilizer N application rates. The agronomic optimal N rates (241 and 185 kg N ha^?1 for wheat and maize, respectively) exhibited great potential for reducing N₂O emissions, by 0.39 (29%) and 1.71 (56%) kg N₂O‐N ha^?1 season^?1 for the wheat and maize seasons, respectively. Mixed application of organic manure with reduced mineral fertilizer N could reduce annual N₂O emissions by 16% relative to mineral N application alone while maintaining a high crop yield. Compared with conventional tillage, no‐tillage significantly reduced N₂O emissions by ~30% in the wheat season, whereas it increased those emissions by ~10% in the maize season. This may have resulted from the lower soil temperature in winter and increased soil moisture in summer under no‐tillage practice. Straw incorporation significantly increased annual N₂O emissions, by 26% relative to straw removal. Our analysis indicates that these farming practices could be further tested to mitigate GHG emission and maintain high crop yields in the NCP .     

High emissions of greenhouse gases from grasslands on peat and other organic soils

Drainage has turned peatlands from a carbon sink into one of the world's largest greenhouse gas (GHG) sources from cultivated soils. We analyzed a unique data set (12 peatlands, 48 sites and 122 annual budgets) of mainly unpublished GHG emissions from grasslands on bog and fen peat as well as other soils rich in soil organic carbon (SOC) in Germany. Emissions and environmental variables were measured with identical methods. Site‐averaged GHG budgets were surprisingly variable (29.2 ± 17.4 t CO₂‐eq. ha^?1 yr^?1) and partially higher than all published data and the IPCC default emission factors for GHG inventories. Generally, CO₂ (27.7 ± 17.3 t CO₂ ha^?1 yr^?1) dominated the GHG budget. Nitrous oxide (2.3 ± 2.4 kg N₂O‐N ha^?1 yr^?1) and methane emissions (30.8 ± 69.8 kg CH₄‐C ha^?1 yr^?1) were lower than expected except for CH₄ emissions from nutrient‐poor acidic sites. At single peatlands, CO₂ emissions clearly increased with deeper mean water table depth (WTD), but there was no general dependency of CO₂ on WTD for the complete data set. Thus, regionalization of CO₂ emissions by WTD only will remain uncertain. WTD dynamics explained some of the differences between peatlands as sites which became very dry during summer showed lower emissions. We introduced the aerated nitrogen stock (N_air) as a variable combining soil nitrogen stocks with WTD. CO₂ increased with N_air across peatlands. Soils with comparatively low SOC concentrations showed as high CO₂ emissions as true peat soils because N_air was similar. N₂O emissions were controlled by the WTD dynamics and the nitrogen content of the topsoil. CH₄ emissions can be well described by WTD and ponding duration during summer. Our results can help both to improve GHG emission reporting and to prioritize and plan emission reduction measures for peat and similar soils at different scales.     

Nitrogen deposition and greenhouse gas emissions from grasslands: uncertainties and future directions

Increases in atmospheric nitrogen deposition (N_dep) can strongly affect the greenhouse gas (GHG; CO₂, CH₄, and N₂O) sink capacity of grasslands as well as other terrestrial ecosystems. Robust predictions of the net GHG sink strength of grasslands depend on how experimental N loads compare to projected N_dep rates, and how accurately the relationship between GHG fluxes and N_dep is characterized. A literature review revealed that the vast majority of experimental N loads were higher than levels these ecosystems are predicted to experience in the future. Using a process‐based biogeochemical model, we predicted that low levels of N_dep either enhanced or reduced the net GHG sink strength of most grasslands, but as experimental N loads continued to increase, grasslands transitioned to a N saturation‐decline stage, where the sensitivity of GHG exchange to further increases in N_dep declined. Most published studies represented treatments well into the N saturation‐decline stage. Our model results predict that the responses of GHG fluxes to N are highly nonlinear and that the N saturation thresholds for GHGs varied greatly among grasslands and with fire management. We predict that during the 21st century some grasslands will be in the N limitation stage where others will transition into the N saturation‐decline stage. The linear relationship between GHG sink strength and N load assumed by most studies can overestimate or underestimate predictions of the net GHG sink strength of grasslands depending on their N baseline status. The next generation of global change experiments should be designed at multiple N loads consistent with future N_dep rates to improve our empirical understanding and predictive ability.     

An agronomic assessment of greenhouse gas emissions from major cereal crops

Agricultural greenhouse gas (GHG) emissions contribute approximately 12% to total global anthropogenic GHG emissions. Cereals (rice, wheat, and maize) are the largest source of human calories, and it is estimated that world cereal production must increase by 1.3% annually to 2025 to meet growing demand. Sustainable intensification of cereal production systems will require maintaining high yields while reducing environmental costs. We conducted a meta‐analysis (57 published studies consisting of 62 study sites and 328 observations) to test the hypothesis that the global warming potential (GWP) of CH₄ and N₂O emissions from rice, wheat, and maize, when expressed per ton of grain (yield‐scaled GWP), is similar, and that the lowest value for each cereal is achieved at near optimal yields. Results show that the GWP of CH₄ and N₂O emissions from rice (3757 kg CO₂ eq ha^?1 season^?1) was higher than wheat (662 kg CO₂ eq ha^?1 season^?1) and maize (1399 kg CO₂ eq ha^?1 season^?1). The yield‐scaled GWP of rice was about four times higher (657 kg CO₂ eq Mg^?1) than wheat (166 kg CO₂ eq Mg^?1) and maize (185 kg CO₂ eq Mg^?1). Across cereals, the lowest yield‐scaled GWP values were achieved at 92% of maximal yield and were about twice as high for rice (279 kg CO₂ eq Mg^?1) than wheat (102 kg CO₂ eq Mg^?1) or maize (140 kg CO₂ eq Mg^?1), suggesting greater mitigation opportunities for rice systems. In rice, wheat and maize, 0.68%, 1.21%, and 1.06% of N applied was emitted as N₂O, respectively. In rice systems, there was no correlation between CH₄ emissions and N rate. In addition, when evaluating issues related to food security and environmental sustainability, other factors including cultural significance, the provisioning of ecosystem services, and human health and well‐being must also be considered.     

有机无机肥配施对双季稻轮作系统产量、温室气体排放和土壤养分的综合效应

本研究开展了连续3年(2017-2019年)的田间试验,通过设置不施肥(CK)、单施化肥(F)、等氮条件下有机肥配施化肥(FM)(有机肥全部于早稻季施用)3个处理,对双季稻轮作系统作物产量、土壤肥力进行分析,并连续2年(2018-2019年)对单施化肥和有机肥配施化肥处理的CH4和N20排放进行监测.结果表明:施肥可以...     

不同氮肥对东北春玉米农田温室气体周年排放的影响

为探明不同氮肥条件下高纬度农田土壤的温室气体排放特性,采用静态箱-气相色谱法研究了常规施氮(CN)、施用缓释肥(SLN)、尿素添加硝化抑制剂和脲酶抑制剂(NIUI)、不施氮肥(NN)对东北春玉米农田土壤温室气体排放的影响.结果表明: CN、SLN和NIUI处理产量分别为9618、9376和9645 kg·hm^-2.与CN处理相比,SLN促进了玉米生长季土壤N₂O的排放,降低了非生长季土壤N₂O的排放;NIUI处理N₂O累积排放量比CN降低了39.0%;各处理土壤CO₂周年累积排放通量无显著差异;东北春玉米田是大气中CH₄的弱汇,NIUI处理较CN促进了玉米生长季土壤对CH₄的吸收.综上,尿素添加脲酶抑制剂和硝化抑制剂可以在实现玉米高产的同时有效减少土壤温室气体排放.     

Molecular mechanisms of water table lowering and nitrogen deposition in affecting greenhouse gas emissions from a Tibetan alpine wetland

Rapid climate change and intensified human activities have resulted in water table lowering (WTL) and enhanced nitrogen (N) deposition in Tibetan alpine wetlands. These changes may alter the magnitude and direction of greenhouse gas (GHG) emissions, affecting the climate impact of these fragile ecosystems. We conducted a mesocosm experiment combined with a metagenomics approach (GeoChip 5.0) to elucidate the effects of WTL (?20 cm relative to control) and N deposition (30 kg N ha^?1 yr^?1) on carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) fluxes as well as the underlying mechanisms. Our results showed that WTL reduced CH₄ emissions by 57.4% averaged over three growing seasons compared with no‐WTL plots, but had no significant effect on net CO₂ uptake or N₂O flux. N deposition increased net CO₂ uptake by 25.2% in comparison with no‐N deposition plots and turned the mesocosms from N₂O sinks to N₂O sources, but had little influence on CH₄ emissions. The interactions between WTL and N deposition were not detected in all GHG emissions. As a result, WTL and N deposition both reduced the global warming potential (GWP) of growing season GHG budgets on a 100‐year time horizon, but via different mechanisms. WTL reduced GWP from 337.3 to ?480.1 g CO₂‐eq m^?2 mostly because of decreased CH₄ emissions, while N deposition reduced GWP from 21.0 to ?163.8 g CO₂‐eq m^?2, mainly owing to increased net CO₂ uptake. GeoChip analysis revealed that decreased CH₄ production potential, rather than increased CH₄ oxidation potential, may lead to the reduction in net CH₄ emissions, and decreased nitrification potential and increased denitrification potential affected N₂O fluxes under WTL conditions. Our study highlights the importance of microbial mechanisms in regulating ecosystem‐scale GHG responses to environmental changes.     

Offsetting global warming‐induced elevated greenhouse gas emissions from an arable soil by biochar application

Global warming will likely enhance greenhouse gas (GHG) emissions from soils. Due to its slow decomposability, biochar is widely recognized as effective in long‐term soil carbon (C) sequestration and in mitigation of soil GHG emissions. In a long‐term soil warming experiment (+2.5 °C, since July 2008) we studied the effect of applying high‐temperature Miscanthus biochar (0, 30 t/ha, since August 2013) on GHG emissions and their global warming potential (GWP) during 2 years in a temperate agroecosystem. Crop growth, physical and chemical soil properties, temperature sensitivity of soil respiration (R_s), and metabolic quotient (qCO₂) were investigated to yield further information about single effects of soil warming and biochar as well as on their interactions. Soil warming increased total CO₂ emissions by 28% over 2 years. The effect of warming on soil respiration did not level off as has often been observed in less intensively managed ecosystems. However, the temperature sensitivity of soil respiration was not affected by warming. Overall, biochar had no effect on most of the measured parameters, suggesting its high degradation stability and its low influence on microbial C cycling even under elevated soil temperatures. In contrast, biochar × warming interactions led to higher total N₂O emissions, possibly due to accelerated N‐cycling at elevated soil temperature and to biochar‐induced changes in soil properties and environmental conditions. Methane uptake was not affected by soil warming or biochar. The incorporation of biochar‐C into soil was estimated to offset warming‐induced elevated GHG emissions for 25 years. Our results highlight the suitability of biochar for C sequestration in cultivated temperate agricultural soil under a future elevated temperature. However, the increased N₂O emissions under warming limit the GHG mitigation potential of biochar.     

Life cycle greenhouse gas emissions of furniture and bioenergy production from oil palm trunks

The palm oil industry constantly attempts to increase the sustainability along the entire palm oil value chain. One important strategy is to utilize all co‐products. Oil palm trunks, which become available upon replanting of existing plantations, represent an important and increasing flow of underexploited biomass. In recent years, innovative technologies are emerging to use them for producing furniture or plywood or providing bioenergy. We assessed the life cycle greenhouse gas emissions of such products and the greenhouse gas emission savings due to replaced alternative products. Although challenging material properties result in a relatively high energy demand and related greenhouse gas emissions in the oil palm wood processing, substantial reductions in greenhouse gas emissions can arise from producing furniture or bioenergy from oil palm trunks, especially if the process energy demand is met by the energy recovery from oil palm wood‐processing residues.     

Soil and greenhouse gas responses to biochar additions in a temperate hardwood forest

Biochar additions can improve soil fertility and sequester carbon, but biochar effects have been investigated primarily in agricultural systems. Biochar from spruce and maple sawdust feedstocks (with and without inorganic phosphorus in a factorial design) were added to plots in a commercially managed temperate hardwood forest stand in central Ontario, Canada; treatments were applied as a top‐dressing immediately prior to fall leaf abscission in September 2011. Forests in this region have acidic, sandy soils, and due to nitrogen deposition may exhibit phosphorus, calcium, and magnesium limitation. To investigate short‐term impacts of biochar application on soil nutrient supply and greenhouse gas fluxes as compared to phosphorus fertilization, data were collected over the first year after treatment application; linear mixed models were used to analyze data. Two to six weeks after treatment application, there were higher concentrations of potassium in spruce and maple biochar plots, and phosphorus in spruce biochar plots, as compared to the control treatment. There were higher concentrations of calcium, magnesium, and phosphorus in the phosphorus plots. In the following spring and summer (9–12 months after treatment application), there were higher soil calcium concentrations in maple biochar plots, and phosphorus plots still had higher soil phosphorus concentrations than control plots. No treatment effects on fluxes of carbon dioxide, methane, or nitrous oxide were detected in the field; however, laboratory incubations after 12 months showed higher microbial respiration in soils from maple biochar plots as compared to spruce biochar, despite no effect on microbial biomass. The results suggest that the most important short‐term impact of biochar additions in this system is the increased supply of the limiting plant nutrients phosphorus and calcium. We expect that larger changes in mineral soil physical and chemical properties will occur when the surface‐applied biochar becomes incorporated into the soil after a few years.     

Comparison of different modeling approaches to better evaluate greenhouse gas emissions from whole wastewater treatment plants

New tools are being developed to estimate greenhouse gas (GHG) emissions from wastewater treatment plants (WWTPs). There is a trend to move from empirical factors to simple comprehensive and more complex process‐based models. Thus, the main objective of this study is to demonstrate the importance of using process‐based dynamic models to better evaluate GHG emissions. This is tackled by defining a virtual case study based on the whole plant Benchmark Simulation Model Platform No. 2 (BSM2) and estimating GHG emissions using two approaches: (1) a combination of simple comprehensive models based on empirical assumptions and (2) a more sophisticated approach, which describes the mechanistic production of nitrous oxide (N₂O) in the biological reactor (ASMN) and the generation of carbon dioxide (CO₂) and methane (CH₄) from the Anaerobic Digestion Model 1 (ADM1). Models already presented in literature are used, but modifications compared to the previously published ASMN model have been made. Also model interfaces between the ASMN and the ADM1 models have been developed. The results show that the use of the different approaches leads to significant differences in the N₂O emissions (a factor of 3) but not in the CH₄ emissions (about 4%). Estimations of GHG emissions are also compared for steady‐state and dynamic simulations. Averaged values for GHG emissions obtained with steady‐state and dynamic simulations are rather similar. However, when looking at the dynamics of N₂O emissions, large variability (3–6 ton CO₂e day^?1) is observed due to changes in the influent wastewater C/N ratio and temperature which would not be captured by a steady‐state analysis (4.4 ton CO₂e day^?1). Finally, this study also shows the effect of changing the anaerobic digestion volume on the total GHG emissions. Decreasing the anaerobic digester volume resulted in a slight reduction in CH₄ emissions (about 5%), but significantly decreased N₂O emissions in the water line (by 14%). Biotechnol. Bioeng. 2012; 109: 2854–2863. © 2012 Wiley Periodicals, Inc.     

Canopy soil greenhouse gas dynamics in response to indirect fertilization across an elevation gradient of tropical montane forests

Canopy soils can significantly contribute to aboveground labile biomass, especially in tropical montane forests. Whether they also contribute to the exchange of greenhouse gases is unknown. To examine the importance of canopy soils to tropical forest‐soil greenhouse gas exchange, we quantified gas fluxes from canopy soil cores along an elevation gradient with 4 yr of nutrient addition to the forest floor. Canopy soil contributed 5–12 percent of combined (canopy + forest floor) soil CO₂ emissions but CH₄ and N₂O fluxes were low. At 2000 m, phosphorus decreased CO₂ emissions (>40%) and nitrogen slightly increased CH₄ uptake and N₂O emissions. Our results show that canopy soils may contribute significantly to combined soil greenhouse gas fluxes in montane regions with high accumulations of canopy soil. We also show that changes in fluxes could occur with chronic nutrient deposition.     

Estimation of nitrous oxide, nitric oxide and ammonia emissions from croplands in East, Southeast and South Asia

Agricultural activities have greatly altered the global nitrogen (N) cycle and produced nitrogenous gases of environmental significance. More than half of all chemical N fertilizer produced globally is used in crop production in East, Southeast and South Asia, where rice is central to nutrition. Emissions of nitrous oxide (N₂O), nitric oxide (NO) and ammonia (NH₃) from croplands in this region were estimated by considering background emission and emissions resulting from N added to croplands, including chemical N, animal manure, biologically fixed N and N in crop residues returned to fields. Background emission fluxes of N₂O and NO from croplands were estimated to be 1.22 and 0.57 kg N ha^?1 yr^?1, respectively. Separate fertilizer‐induced emission factors were estimated for upland fields and rice fields. Total N₂O emission from croplands in the study region was estimated to be 1.19 Tg N yr^?1, with 43% contributed by background emissions. The average fertilizer‐induced N₂O emission, however, accounts for only 0.93% of the applied N, which is less than the default IPCC value of 1.25%, because of the low emission factor from paddy fields. Total NO emission was 591 Gg N yr^?1 in the study region, with 40% from background emissions. The average fertilizer‐induced NO emission factor was 0.48%. Total NH₃ emission was estimated to be 11.8 Tg N yr^?1. The use of urea and ammonium bicarbonate and the cultivation of rice led to a high average NH₃ loss rate from chemical N fertilizer in the study region. Emissions were displayed at a 0.5° × 0.5° resolution with the use of a global landuse database.     

Methane and nitrous oxide emissions from rice paddy fields as affected by nitrogen fertilisers and water management

Methane and N₂O emissions affected by nitrogen fertilisers were measured simultaneously in rice paddy fields under intermittent irrigation in 1994. Ammonium sulphate and urea were applied at rates of 0 (control), 100 and 300 kg N ha^-1. The results showed that CH₄ emission, on the average, decreased by 42 and 60% in the ammonium sulphate treatments and 7 and 14% in the urea treatments at rates of 100 and 300 kg N ha^-1, respectively, compared to the control. N₂O emission increased significantly with the increase in the nitrogen application rate. N₂O emission was higher from ammonium sulphate treatments than from the urea treatments at the same application rate. A trade-off effect between CH₄ and N₂O emission was clearly observed. The N₂O flux was very small when the rice paddy plots were flooded, but peaked at the beginning of the disappearance of floodwater. In contrast, the CH₄ flux peaked during flooding and was significantly depressed by mid-season aeration (MSA). The results suggest that it is important to evaluate the integrative effects of water management and fertiliser application for mitigating greenhouse gas emissions in order to attenuate the greenhouse effect contributed by rice paddy fields.     

生物质炭化还田对稻田温室气体排放及土壤理化性质的影响

通过水稻种植田间试验,研究了水稻秸秆直接还田、水稻秸秆与生活垃圾炭化后还田对稻田温室气体CH4、CO2和N2O排放及土壤理化性质和水稻产量的影响.结果表明:与直接还田相比,秸秆炭化后还田可显著降低稻田CH4和N2O的累积排放量,降幅分别为64.2%～78.5%和16.3%～18.4%.与不添加生物炭相比,无论种植水稻与否,添加秸秆炭和垃圾炭均显著降低了稻田N2O的累积排放量;不种植水稻情况下,添加垃圾炭显著降低了稻田CO2的累积排放量,降幅为25.3%.秸秆炭对提高稻田土壤pH和速效钾含量的作用优于垃圾炭.两种生物炭均能显著提高稻田土壤有机碳含量,但对土壤容重、全氮、有效磷、阳离子交换量及水稻籽粒产量均未产生显著影响.与秸秆直接还田相比,秸秆炭化后还田对水稻增产的效果更佳.     

Soil organic matter quality influences mineralization and GHG emissions in cryosols: a field‐based study of sub‐ to high Arctic

Arctic soils store large amounts of labile soil organic matter (SOM) and several studies have suggested that SOM characteristics may explain variations in SOM cycling rates across Arctic landscapes and Arctic ecosystems. The objective of this study was to investigate the influence of routinely measured soil properties and SOM characteristics on soil gross N mineralization and soil GHG emissions at the landscape scale. This study was carried out in three Canadian Arctic ecosystems: Sub‐Arctic (Churchill, MB), Low‐Arctic (Daring Lake, NWT), and High‐Arctic (Truelove Lowlands, NU). The landscapes were divided into five landform units: (1) upper slope, (2) back slope, (3) lower slope, (4) hummock, and (5) interhummock, which represented a great diversity of Static and Turbic Cryosolic soils including Brunisolic, Gleysolic, and Organic subgroups. Soil gross N mineralization was measured using the ¹⁵N dilution technique, whereas soil GHG emissions (N₂O, CH₄, and CO₂) were measured using a multicomponent Fourier transform infrared gas analyzer. Soil organic matter characteristics were determined by (1) water‐extractable organic matter, (2) density fractionation of SOM, and (3) solid‐state CPMAS ¹³C nuclear magnetic resonance (NMR) spectroscopy. Results showed that gross N mineralization, N₂O, and CO₂ emissions were affected by SOM quantity and SOM characteristics. Soil moisture, soil organic carbon (SOC), light fraction (LF) of SOM, and O‐Alkyl‐C to Aromatic‐C ratio positively influenced gross N mineralization, N₂O and CO₂ emissions, whereas the relative proportion of Aromatic‐C negatively influenced those N and C cycling processes. Relationships between SOM characteristics and CH₄ emissions were not significant throughout all Arctic ecosystems. Furthermore, results showed that lower slope and interhummock areas store relatively more labile C than upper and back slope locations. These results are particularly important because they can be used to produce better models that evaluate SOM stocks and dynamics under several climate scenarios and across Arctic landscapes and ecosystems.     

Carbohydrate-rich supplements can improve nitrogen use efficiency and mitigate nitrogenous gas emissions from the excreta of dairy cows grazing temperate grass

Temperate pasture species constitute a source of protein for dairy cattle. On the other hand, from an environmental perspective, their high N content can increase N excretion and nitrogenous gas emissions by livestock. This work explores the effect of energy supplementation on N use efficiency (NUE) and nitrogenous gas emissions from the excreta of dairy cows grazing a pasture of oat and ryegrass. The study was divided into two experiments: an evaluation of NUE in grazing dairy cows, and an evaluation of N-NH₃ and N-N₂O volatilizations from dairy cow excreta. In the first experiment, 12 lactating Holstein × Jersey F1 cows were allocated to a double 3 × 3 Latin square (three experimental periods of 17 days each) and subjected to three treatments: cows without supplementation (WS), cows supplemented at 4.2 kg DM of corn silage (CS) per day, and cows supplemented at 3.6 kg DM of ground corn (GC) per day. In the second experiment, samples of excreta were collected from the cows distributed among the treatments. Aliquots of dung and urine of each treatment plus one blank (control – no excreta) were allotted to a randomized block design to evaluate N-NH₃ and N-N₂O volatilization. Measurements were performed until day 25 for N-NH₃ and until day 94 for N-N₂O. Dietary N content in the supplemented cows was reduced by 20% (P < 0.001) compared with WS cows, regardless of the supplement. Corn silage cows had lower N intake (P < 0.001) than WS and GC cows (366 v. 426 g/day, respectively). Ground corn supplementation allowed cows to partition more N towards milk protein compared with the average milk protein of WS cows or those supplemented with corn silage (117 v. 108 g/day, respectively; P < 0.01). Thus, even though they were in different forms, both supplements were able to increase (P < 0.01) NUE from 27% in WS cows to 32% in supplemented cows. Supplementation was also effective in reducing N excretion (761 v. 694 g/kg of N_intake; P < 0.001), N-NH₃ emission (478 v. 374 g/kg of N_milk; P < 0.01) and N-N₂O emission (11 v. 8 g/kg of N_milk; P < 0.001). Corn silage and ground corn can be strategically used as feed supplements to improve NUE, and they have the potential to mitigate N-NH₃ and N-N₂O emissions from the excreta of dairy cows grazing high-protein pastures.