Effect of crop residue incorporation on soil organic carbon and greenhouse gas emissions in European agricultural soils

Soil organic matter (SOM) improves soil physicochemical and biological properties, and the sequestration of carbon in SOM may mitigate climate change. Soil organic carbon (SOC) often decreases in intensive cropping systems. Incorporation of crop residues (CR) may be a sustainable management practice to maintain the SOC levels and to increase soil fertility. This study quantifies the effects of CR incorporation on SOC and greenhouse gas (GHG) emissions (CO₂ and N₂O) in Europe using data from long‐term experiments. Response ratios (RRs) for SOC and GHG emissions were calculated between CR incorporation and removal. The influence of environmental zones (ENZs), clay content and experiment duration on the RRs was investigated. We also studied how RRs of SOC and crop yields were correlated. A total of 475 RRs were derived from 39 publications. The SOC increased by 7% following CR incorporation. In contrast, in a subsample of cases, CO₂ emissions were six times and N₂O emissions 12 times higher following CR incorporation. The ENZ had no significant influence on RRs. For SOC concentration, soils with a clay content >35% showed 8% higher RRs compared with soils with clay contents between 18 and 35%. As the experiment progressed, RR for SOC concentration increased. For N₂O emissions, RR was significantly greater in experiments with a duration <5 yr compared with 11–20 yr. No significant correlations were found between RR for SOC concentration and yields, but differences between sites and study durations were detected. We suggest that a long duration of crop residue incorporation is a win‐win scenario under a continental climate. We conclude that CR incorporation is important for maintaining SOC, but its influence on GHG emissions should be taken into account as well.     

Nutrient and trace element concentrations influence greenhouse gas emissions from Malaysian tropical peatlands

Tropical peatlands are unique and globally important ecosystems for carbon storage that are generally considered nutrient poor. However, different nutrient and trace element concentrations in these complex ecosystems and their interactions with carbon emissions are largely unknown. The objective of this research was to explore the concentrations of macro‐ and micronutrients and othertrace elements in surface peats, and their relationship with greenhouse gas emissions in North Selangor peatlands subjected to different land use. All nutrient and trace element concentrations except chromium exhibited significant differences between sites. Most macronutrients and some micronutrients showed significant differences between seasons, typically with a reduction over time from wet to dry seasons, possibly due to leaching. CO₂ emissions were positively related to organic matter content and manganese concentrations and negatively correlated with selenium. CH₄ emissions were positively correlated with organic matter content, manganese, copper, barium, cobalt and aluminium, and negatively correlated with molybdenum, selenium, lithium and vanadium. This research has detected loss of essential nutrients over time, aiding to increase nutrient limitation in tropical peatlands due to drainage. The observed significant correlation between trace elements and greenhouse gas emissions strengthens the importance of including trace element analyses in understanding the biogeochemical functions of these understudied peatlands.     

Biochar application to soil for climate change mitigation by soil organic carbon sequestration

Pyrogenic carbon (C) is produced by incomplete combustion of fuels including organic matter (OM). Certain ranges in the combustion continuum are termed ‘black carbon' (BC). Because of its assumed persistence, surface soils in large parts of the world contain BC with up to 80% of surface soil organic C (SOC) stocks and up to 32% of subsoil SOC in agricultural soils consisting of BC. High SOC stocks and high levels of soil fertility in some ancient soils containing charcoal (e.g., terra preta de Índio) have recently been used as strategies for soil applications of biochar, an engineered BC material similar to charcoal but with the purposeful use as a soil conditioner (1) to mitigate increases in atmospheric carbon dioxide (CO₂) by SOC sequestration and (2) to enhance soil fertility. However, effects of biochar on soils and crop productivity cannot be generalized as they are biochar‐, plant‐ and site‐specific. For example, the largest potential increases in crop yields were reported in areas with highly weathered soils, such as those characterizing much of the humid tropics. Soils of high inherent fertility, characterizing much of the world's important agricultural areas, appear to be less likely to benefit from biochar. It has been hypothesized that both liming and aggregating/moistening effects of biochar improved crop productivity. Meta‐analyses of biochar effects on SOC sequestration have not yet been reported. To effectively mitigate climate change by SOC sequestration, a net removal of C and storage in soil relative to atmospheric CO₂ must occur and persist for several hundred years to a few millennia. At deeper soil depths, SOC is characterized by long turnover times, enhanced stabilization, and less vulnerability to loss by decomposition and erosion. In fact, some studies have reported preferential long‐term accumulation of BC at deeper depths. Thus, it is hypothesized that surface applied biochar‐C (1) must be translocated to subsoil layers and (2) result in deepening of SOC distribution for a notable contribution to climate change mitigation. Detailed studies are needed to understand how surface‐applied biochar can move to deeper soil depths, and how its application affects organic C input to deeper soil depths. Based on this knowledge, biochar systems for climate change mitigation through SOC sequestration can be designed. It is critically important to identify mechanisms underlying the sometimes observed negative effects of biochar application on biomass, yield and SOC as biochar may persist in soils for long periods of time as well as the impacts on downstream environments and the net climate impact when biochar particles become airborne.     

Nutrient cycling and greenhouse gas emissions from soil amended with biochar-manure mixtures

Integrating biochar into cattle diets has recently emerged as a potential management practice for improving on-farm productivity.Yet,information concerning the cycling of biochar-manure mixtures is scarce.A 70-d incubation experiment was conducted within two surface(0–15 cm)Mollisols with contrasting textures,i.e.,sandy clay loam(Raymond)and clayey(Lethbridge),to evaluate the effects of biochar(3 Mg ha^-1)on cumulative greenhouse gas(GHG)emissions and related fertility attributes in the presence or absence of cattle manure(120 Mg ha^-1).Five treatments were included:i)non-amended soil(control,CK),ii)soil amended with pinewood biochar(B),iii)soil amended with beef cattle manure(M)(manure from cattle on a control diet),iv)soil amended with biochar-manure(BM)(manure from cattle on a control diet,with pinewood biochar added at 20 g kg^-1of diet dry matter),and v)soil amended with B and M at the aforementioned rates(B+M).A total of 40 soil columns were prepared and incubated at 21℃and 60%–80%water-holding capacity.On average,total CO₂fluxes increased by 2.2-and 3.8-fold under manure treatments(i.e.,M,BM,and B+M),within Raymond and Lethbridge soils,respectively,relative to CK and B.Similarly,total CH4 fluxes were the highest(P<0.05)in Raymond soil under B+M and BM relative to CK and B,and in Lethbridge soil under M and BM relative to CK and B.In Lethbridge soil,application of BM increased cumulative N₂O emissions by 1.8-fold relative to CK.After 70-d incubation,amendment with BM increased(P<0.05)PO_4-P and NO_3-N+NH_4-N availability in Raymond and Lethbridge soils compared with B.A similar pattern was observed for water-extractable organic carbon in both soils,with BM augmenting(P<0.05)the occurrence of labile carbon over CK and B.It can be concluded that biochar,manure,and/or biochar-manure have contrasting short-term effects on the biogeochemistry of Mollisols.At relatively low application rates,biochar does not necessarily counterbalance manure-derived inputs.Although BM did not mitigate the flux of GHGs over M,biochar-manure has the potential to recycle soil nutrients in semiarid drylands.     

耕作与轮作方式对黑土有机碳和全氮储量的影响

土壤有机碳(SOC)及全氮(TN)对土壤肥力、作物产量、农业可持续发展以及全球碳、氮循环等都具有重要影响。为探索不同耕作和轮作方式对耕层黑土SOC和TN储量的影响,本文以吉林省德惠市进行了8 a的田间定位试验中层黑土为研究对象,对免耕、垄作和秋翻三种耕作方式及玉米-大豆轮作和玉米连作两种轮作方式下SOC和TN在各土层的含量变化进行了分析,并采用等质量土壤有机质储量计算方法,对比分析了不同处理对0～30 cm SOC和TN储量的影响。结果表明,与试验开始前相比,玉米-大豆轮作系统中,秋翻下SOC和TN储量均有所降低;免耕显著增加了0～5 cm SOC及TN含量,但SOC在亚表层亏损,导致其储量并未增加;而垄作处理下SOC及TN含量在0～5、5～10 cm的均显著增加,0～30 cm储量亦分别增加了4.9%和10.7%。玉米连作系统的两种耕作处理(免耕和秋翻)下SOC和TN储量均有所增加,且TN储量增幅均高于玉米-大豆轮作系统,其中免耕下TN储量增幅是玉米-大豆轮作的3.2倍。所有处理下C/N均呈降低趋势,其中垄作0～5 cm C/N由12.05降至11.04,降低幅度分别是免耕和秋翻的3.2和2.8倍。综上可知,对质地黏重排水不良的中层黑土,玉米-大豆轮作系统下免耕并不是促进SOC固定的有效形式,而垄作则促进了黑土SOC和TN的积累,这不仅有利于土壤肥力的改善,而且是使农田黑土由CO2"源"变为"汇"的有效形式之一。与玉米-大豆轮作相比,玉米连作下三种耕作方式都有利于SOC和TN积累。     

Mitigation of greenhouse gas emissions from soil under silage production by use of organic manures or slow-release fertilizer

Abstract. Grassland is a major source of nitrous oxide (N₂O) and methane (CH₄) emissions in the UK, resulting from high rates of fertilizer application. We studied the effects of substituting mineral fertilizer by organic manures and a slow-release fertilizer in silage grass production on greenhouse gas emissions and soil mineral N content in a three-year field experiment. The organic manures investigated were sewage sludge pellets and composted sewage sludge (dry materials), and digested sewage sludge and cattle slurry (liquid materials). The organic manures produced N₂O and carbon dioxide (CO₂) consistently from time of application up to harvest. However, they mitigated N₂O emissions by around 90% when aggregate emissions of 15.7 kg N ha⁻¹ from NPK fertilizer were caused by a flux of up to 4.9 kg N ha⁻¹ d⁻¹ during the first 4 days after heavy rainfall subsequent to the NPK fertilizer application. CH₄ was emitted only for 2 or 3 days after application of the liquid manures. CH₄ and CO₂ fluxes were not significantly mitigated. Composting and dried pellets were useful methods of conserving nutrients in organic wastes, enabling slow and sustained release of nitrogen. NPK slow-release fertilizer also maintained grass yields and was the most effective substitute for the conventional NPK fertilizer for mitigation of N₂O fluxes.     

耕作方式对华北农田土壤有机碳储量及温室气体排放的影响

耕作方式能够改变土壤有机碳在土层中的分布,进而对土壤有机碳及土壤碳储量产生影响。该研究在模型调整的基础上选取了土壤有机碳(SOC)、土壤碳密度(SCD)、土壤呼吸(SR)以及生物量碳(BC)4个指标对DNDC(denitrification-decomposition)模型在华北麦-玉两熟农田的适用性进行验证,并用该模型模拟当地土壤碳储量(SCS)动态变化以及温室气体排放特征。结果表明,模型模拟值与实测值吻合良好,此模型可以适用于华北麦-玉两熟农田土壤有机碳的模拟研究;2001-2010年SOC和SCS逐年递增;对未来100a模拟发现,前15a旋耕(RT)和翻耕(CT)处理SOC增长迅速,而免耕(NT)SOC的剧烈增长趋势要持续近40a;对比各处理100a碳储量变化可知,前20aCT处理SCS最大,20a后NT处理SCS最大;各处理土壤全球变暖潜势(GWP)大小为CT>RT>NT。通过验证该文证明了DNDC模型可以较好地研究华北麦-玉两熟农田土壤碳循环;长久来看NT有利于农田SCS的积累以及GWP的降低。该研究能够为华北麦-玉两熟农作区固碳减排提供依据。     

Soil tillage and cover crop on soil CO2 emissions from sugarcane fields

Soil tillage is an agricultural practice that directly affects the global carbon cycle. Our study sought to assess the implications of adopting sunn hemp cover crops with different tillage practices on CO₂ emissions for two soil types (clayey and sandy soil) cultivated with sugarcane in Brazil. The experimental design was a split‐plot with randomized blocks, with the main plots being with cover crop or fallow and sub‐plots being under conventional or minimum tillage. Our results indicate that during the first 50 days after soil tillage, the variation in soil CO₂ emissions was stimulated by cover crop and soil tillage, while after that, it became dominated by the root respiration of sugarcane plants. We also found that over the first 97 days after the tillage, the clayey soil showed differences between minimum tillage with cover crop and fallow. Conversely, for sandy soil over the first 50 days following, there were differences between the tillage systems under cover cropping. Emissions from sugarcane rows were found to be greater than those from inter‐row positions. We concluded that soils under different textural classes had distinct patterns in terms of soil CO₂ emissions. The correct quantification of CO₂ emissions during the sugarcane renovation period should prioritize having a short assessment period (~50 days after soil tillage) as well as including measurements at row and inter‐row positions.     

Effects of biochar amendment on greenhouse gas emissions,net ecosystem carbon budget and properties of an acidic soil under intensive vegetable production

Biochar addition to soils has been frequently proposed as a means to increase soil fertility and carbon (C) sequestration. However, the effect of biochar addition on greenhouse gas emissions from intensively managed soils under vegetable production at the field scale is poorly understood. The effects of wheat straw biochar amendment with mineral fertilizer or an enhanced‐efficiency fertilizer (mixture of urea and nitrapyrin) on N₂O efflux and the net ecosystem C budget were investigated for an acidic soil in southeast China over a 1‐yr period. Biochar addition did not affect the annual N₂O emissions (26–28 kg N/ha), but reduced seasonal N₂O emissions during the cold period. Biochar increased soil organic C and CO₂ efflux on average by 61 and 19%, respectively. Biochar addition greatly increased C gain in the acidic soil (average 11.1 Mg C/ha) compared with treatments without biochar addition (average ?2.2 Mg C/ha). Biochar amendment did not increase yield‐scaled N₂O emissions after application of mineral fertilizer, but it decreased yield‐scaled N₂O by 15% after nitrapyrin addition. Our results suggest that biochar amendment of acidic soil under intensive vegetable cultivation contributes to soil C sequestration, but has only small effects on both plant growth and greenhouse gas emissions.     

Consequences of feasible future agricultural land‐use change on soil organic carbon stocks and greenhouse gas emissions in Great Britain

The aim of this study was to assess the consequences of feasible land‐use change in Great Britain on GHG emissions mainly through the gain or loss of soil organic carbon. We use estimates of per‐area changes in soil organic carbon (SOC) stocks and in greenhouse gas (GHG) emissions, coupled with Great Britain (GB) county‐level scenarios of land‐use change based on historical land‐use patterns or feasible futures to estimate the impact of potential land‐use change between agricultural land‐uses. We consider transitions between cropland, temporary grassland (<5 yr under grass), permanent grass (>5 yr under grass) and forest. We show that reversion to historical land‐use patterns as present in 1930 could result in GHG emission reductions of up to ca. 11 Mt CO₂‐eq./yr (relative to a 2004 baseline), because of an increased permanent grassland area. By contrast, cultivation of 20% of the current (2004) permanent grassland area for crop production could result in GHG emission increases of up to ca. 14 Mt CO₂‐eq./yr. We conclude that whilst change between agricultural land‐uses (transitions between permanent and temporary grassland and cropland) in GB is likely to be a limited option for GHG mitigation, external factors such as agricultural product commodity markets could influence future land‐use. Such agricultural land‐use change in GB could have significant impacts on Land‐use, Land‐Use Change and Forestry (LULUCF) emissions, with relatively small changes in land‐use (e.g. 5% plough out of grassland to cropland, or reversion of cropland to the grassland cover in Nitrate Vulnerable Zones of 1998) having an impact on GHG emissions of a similar order of magnitude as the current United Kingdom LULUCF sink. In terms of total UK GHG emissions, however, even the most extreme feasible land‐use change scenarios account for ca. 2% of current national GHG emissions.     

Tropical savannah woodland: effects of experimental fire on soil microorganisms and soil emissions of carbon dioxide

Burning of the vegetation in the African savannahs in the dry season is widespread and may have significant effects on soil chemical and biological properties. A field experiment in a full factorial randomised block design with fire, ash and extra grass biomass as main factors was carried out in savannah woodland of the Gambella region in Ethiopia. The microbial biomass C (C_mic) was 52% (fumigation-extraction) and 20% (substrate-induced respiration) higher in burned than unburned plots 12 d after burning. Both basal respiration and potential denitrification enzyme activity (PDA) immediately responded to burning and increased after treatment. However, in burned plots addition of extra biomass (fuel load) led to a reduction of C_mic and PDA due to enhanced fire temperature. Five days after burning, there was a short-lived burst in the in situ soil respiration following rainfall, with twice as high soil respiration in burned than unburned plots. In contrast, 12 d after burning soil respiration was 21% lower in the burned plots, coinciding with lower soil water content in the same plots. The fire treatment resulted in higher concentrations of dissolved organic C (24-85%) and nitrate (47-76%) in the soil until 90 d after burning, while soil NH₄⁺-N was not affected to the same extent. The increase in soil NO₃⁻-N but not NH₄⁺-N in the burned plots together with the well-aerated soil conditions indicated that nitrifying bacteria were stimulated by fire and immediately oxidised NH₄⁺-N to NO₃⁻-N. In the subsequent rainy season, NO₃⁻-N and, consequently, PDA were reduced by ash deposition. Further, C_mic was lower in burned plots at that time. However, the fire-induced changes in microbial biomass and activity were relatively small compared to the substantial seasonal variation, suggesting transient effects of the low severity experimental fire on soil microbial functioning.     

Functional dependencies of soil CO2 emissions on soil biological properties in northern German agricultural soils derived from a glacial till

Agricultural soil CO₂ emissions and their controlling factors have recently received increased attention because of the high potential of carbon sequestration and their importance in soil fertility. Several parameters of soil structure, chemistry, and microbiology were monitored along with soil CO₂ emissions in research conducted in soils derived from a glacial till. The investigation was carried out during the 2012 growing season in Northern Germany. Higher potentials of soil CO₂ emissions were found in grassland (20.40 µg g^?1 dry weight h^?1) compared to arable land (5.59 µg g^?1 dry weight h^?1) within the incubating temperature from 5°C to 40°C and incubating moisture from 30% to 70% water holding capacity (WHC) of soils taken during the growing season. For agricultural soils regardless of pasture and arable management, we suggested nine key factors that influence changes in soil CO₂ emissions including soil temperature, metabolic quotient, bulk density, WHC, percentage of silt, bacterial biomass, pH, soil organic carbon, and hot water soluble carbon (glucose equivalent) based on principal component analysis and hierarchical cluster analysis. Slightly different key factors were proposed concerning individual land use types, however, the most important factors for soil CO₂ emissions of agricultural soils in Northern Germany were proved to be metabolic quotient and soil temperature. Our results are valuable in providing key influencing factors for soil CO₂ emission changes in grassland and arable land with respect to soil respiration, physical status, nutrition supply, and microbe-related parameters.     

Effect of straw biochar application on soil carbon,greenhouse gas emissions and nitrogen leaching: A vegetable crop rotation field experiment

Intensive vegetable crop systems are rapidly developing, with consequences for greenhouse gas (GHGs) emissions, nitrogen leaching and soil carbon. We undertook a field trial to explore the effect of biochar application (0, 10, 20 and 40 t ha⁻¹) on these factors in lettuce, water spinach and ice plant rotation. Our results show that the 20 and 40 t ha⁻¹ soil treatments resulted in the SOC content being 26.3% and 29.8% higher than the control (0 t ha⁻¹), respectively, with significant differences among all treatments (p < .05). Biochar application caused N₂O emissions to decrease during the lettuce and water spinach seasons, by 1.5%–33.6% and 12.4%–40.5%, respectively, compared the control, with the 20 t ha⁻¹ application rate resulting in the lowest N₂O emissions. Biochar also decreased the dissolved nitrogen (DN) concentration in leachate by 9.8%–36.2%, following a 7.3%–19.9% reduction in dissolved nitrogen in the soil. Similarly, biochar decreased the nitrate (NO₃⁻) concentrations in leachate by 3.9%–30.2%, following a 3.8%–16.7% reduction in the soil nitrate level. Overall, straw biochar applied at rate of 20 t ha⁻¹ produced the lowest N₂O emissions and N leaching, while, increasing soil carbon.     

黄淮海平原集约种植条件下土壤有机质动态模拟

A modified CQESTR model, a simple yet useful model frequently used for estimating carbon sequestration in agricultural soils, was developed and applied to evaluate the effects of intensive cropping on soil organic matter （SOM） dynamics and mineralization as well as to estimate carbon dioxide emission from agricultural soils at seven sites on the Huang-Huai-Hai Plain of China. The model was modified using site-specific parameters from short- and mid-term buried organic material experiments at four stages of biomass decomposition. The predicted SOM results were validated using independent data from seven long-term （10- to 20-year） soil fertility experiments in this region. Regression analysis on 1 151 pairs of predicted and measured SOM data had an r2 of 0.91 （P≤0.01）. Therefore, the modified model was able to predict the mineralization of crop residues, organic amendments, and native SOM. Linear regression also showed that SOM mineralization rate （MR） in the plow layer increased by 0.22% when annual crop yield increased by 1 t ha^-1 （P ≤ 0.01）, suggesting an improvement in SOM quality. Apparently, not only did the annual soil respiration efftux merely reflect the intensity of soil organism and plant metabolism, but also the SOM MR in the plow layer. These results suggested that the modified model was simple yet valuable in predicting SOM trends at a single agricultural field and could be a powerful tool for estimating C-storage potential and reconstructing C storage on the Huang-Huai-Hai Plain of China.     

Impact of intensive agricultural management on carbon and nitrogen dynamics in the humid tropics

ABSTRACT

The concern about global climate change continues to increase research interest regarding carbon and nitrogen dynamics in the soil. This is based on their role in maintaining soil fertility, which can instead be a source of greenhouse gas emissions if not managed properly, while threatening food security. Humid tropical conditions enable intensive agricultural cultivation with various cropping systems to fulfill the demand for agriculture products. Such climate accelerates the soil organic matter decomposition rate so that it strongly influences soil carbon and nitrogen dynamics. However, inappropriate implementation of intensive agricultural systems that does not consider the balance between carbon and nitrogen input and output, negatively affects soil fertility, mainly decreasing soil organic carbon and total soil nitrogen, changing the composition of carbon and nitrogen owing to the loss of soil organic matter through erosion and leaching, thus, causing soil degradation. Mitigation strategies can be performed by using organic matter and crop residue, crop rotation and improvement of crop pattern, soil tillage and fertilization, cover crops and mulch. Sustainable land management for maintenance of soil organic carbon and total soil nitrogen dynamics should be locally and globally developed and adopted for a more sustainable agricultural system. Recovery of soil capacity to accumulate carbon is a strategic step to reduce the impact of climate change. Hence, an intensive study on efficient soil organic carbon management is required to improve food production and mitigation of climate change to attain sustainable development goals in 2030.     

基于DNDC模型的东北地区春玉米农田固碳减排措施研究

春玉米是我国东北地区主要粮食作物,但由于连年耕作和氮肥的高投入,春玉米农田也可能成为重要的温室气体排放源。因此,通过优化田间管理措施在保证作物产量的同时实现固碳减排,对于春玉米种植系统的可持续发展具有重要意义。过程模型（Denitrification Decomposition, DNDC）是评估固碳减排措施的有效工具,本研究在对DNDC模型进行验证的基础上,应用模型研究不同施氮和秸秆还田措施对东北地区春玉米农田固碳和氧化亚氮（N2O）排放的长期综合影响。模型验证结果表明,DNDC模拟的不同处理下土壤呼吸季节总量、 N2O排放季节总量和春玉米产量与田间观测结果较一致;同时模型也能较好地模拟不同处理下土壤呼吸和N2O排放季节变化动态。这表明DNDC模型能较理想地模拟不同施氮和秸秆还田措施对春玉米农田土壤呼吸、 N2O排放和作物产量的影响。利用模型综合分析不同管理情景对产量和土壤固碳减排的长期影响,结果表明: 1）与当地农民习惯施肥相比,优化施氮措施不会明显影响作物产量,能减少N2O排放,且对土壤固碳影响很小,因而能降低温室气体净排放,但净排放降低幅度有限（8%~13%）; 2）在优化施氮措施的同时秸秆还田能在保障供试农田春玉米产量的同时大幅度减少春玉米种植系统温室气体净排放,甚至可能将供试农田由温室气体排放源转变为温室气体吸收汇。本研究结果可为优化管理措施实现春玉米种植系统固碳减排提供科学依据。     

Long‐term cropping systems and tillage management effects on soil organic carbon stock and steady state level of C sequestration rates in a semiarid environment

A calcareous and clayey xeric Chromic Haploxerept of a long‐term experimental site in Sicily (Italy) was sampled (0–15 cm depth) under different land use management and cropping systems (CSs) to study their effect on soil aggregate stability and organic carbon (SOC). The experimental site had three tillage managements (no till [NT], dual‐layer [DL] and conventional tillage [CT]) and two CSs (durum wheat monocropping [W] and durum wheat/faba bean rotation [WB]). The annually sequestered SOC with W was 2·75‐times higher than with WB. SOC concentrations were also higher. Both NT and CT management systems were the most effective in SOC sequestration whereas with DL system no C was sequestered. The differences in SOC concentrations between NT and CT were surprisingly small. Cumulative C input of all cropping and tillage systems and the annually sequestered SOC indicated that a steady state occurred at a sequestration rate of 7·4 Mg C ha⁻¹ y⁻¹. Independent of the CSs, most of the SOC was stored in the silt and clay fraction. This fraction had a high N content which is typical for organic matter interacting with minerals. Macroaggregates (>250 µm) and large microaggregates (75–250 µm) were influenced by the treatments whereas the finest fractions were not. DL reduced the SOC in macroaggregates while NT and CT gave rise to higher SOC contents. In Mediterranean areas with Vertisols, agricultural strategies aimed at increasing the SOC contents should probably consider enhancing the proportion of coarser soil fractions so that, in the short‐term, organic C can be accumulated. Copyright © 2010 John Wiley & Sons, Ltd.     

Meeting the UK's climate change commitments: options for carbon mitigation on agricultural land

Abstract. Under the Kyoto Protocol, the European Union is committed to an 8% reduction in CO₂ emissions, compared to baseline (1990) levels, during the first commitment period (2008–2012). However, within the overall EU agreement, the UK is committed to a 12.5% reduction. In this paper, we estimate the carbon mitigation potential of various agricultural land-management strategies (Kyoto Article 3.4) and examine the consequences of UK and European policy options on the potential for carbon mitigation.
We show that integrated agricultural land management strategies have considerable potential for carbon mitigation. Our figures suggest the following potentials (Tg yr⁻¹) for each scenario: animal manure, 3.7; sewage sludge, 0.3; cereal straw incorporation, 1.9; no-till farming, 3.5; agricultural extensification, 3.3; natural woodland regeneration, 3.2 and bioenergy crop production, 4.1. A realistic land-use scenario combining a number of these individual management options has a mitigation potential of 10.4 Tg C yr⁻¹ (equivalent to about 6.6% of 1990 UK CO₂-carbon emissions). An important resource for carbon mitigation in agriculture is the surplus arable land, but in order to fully exploit it, policies governing the use of surplus arable land would need to be changed. Of all options examined, bioenergy crops show the greatest potential. Bioenergy crop production also shows an indefinite mitigation potential compared to other options where the potential is infinite.
The UK will not attempt to meet its climate change commitments solely through changes in agricultural land-use, but since all sources of carbon mitigation will be important in meeting these commitments, agricultural options should be taken very seriously.     

Large‐scale identification of hot spots for soil carbon demand under climate change and bioenergy production

Global change scenarios predict an increased risk for declining amounts of soil organic matter (SOM) for Central Germany. Within this region the production of bioenergy is one important strategy to counteract the rising anthropogenic CO₂‐emissions. Both issues have a close connection: SOM is an important basis for soil productivity and requires a steady reproduction flux. Bioenergy production requires productive soils and partly consumes plant biomass C. Therefore, the available amount for SOM reproduction is reduced. This study provides a methodology for the large‐scale identification of areas with possible conflicts between bioenergy production and SOM reproduction based on (1) the prediction of climate change impact on SOM reproduction and (2) an analysis of the regional distribution of biogas plants. With the C demand index (CDI) and the capacity index (CAP), two indicators were developed which enable the identification of hot spots of high carbon demand for SOM reproduction due to climate change and the usage of bioenergy. As a result of low data requirements, the indicators are widely applicable and transferable to other large‐scale studies. The proposed methodology was applied to Central Germany as a pilot region. Results indicate a growing demand (10–40%) of fresh organic C from biomass for SOM production in comparison to the current level. The analysis reveals that the bioenergy C demand is not evenly distributed within the study region. It also shows some regional clustering. Furthermore, the analysis identifies certain hot spots of a high C demand, where a high capacity of biogas production may conflict with rising demands for biomass to mitigate climate change effects on SOM storage. The hot spot areas—identified and selected on a large scale—can subsequently be analyzed in more detail on a local to farm scale by using high‐resolution data and models which enable the quantification of soil C dynamics.