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1.
This study investigates the cost of soil carbon sequestration in the Midwest US. The model addresses several missing components in earlier analyses: the link between the residue level choice and carbon payments, crop rotations, carbon loss when shifting from conservation to conventional tillage and the spatial pattern of carbon sequestration across different soil types. The results suggest that for $100 per metric ton of carbon, 1.5 million metric tons of carbon could be sequestered per year on the 19.9 million hectares of cropland in the study region. These estimates suggest less carbon potential than existing studies because the opportunity costs associated with conservation tillage are fairly high. Annual carbon rental payments are found to be more efficient, as expected, but for smaller programs, per hectare rental payments are not substantially more costly.  相似文献   

2.
Agricultural suitability maps are a key input for land use zoning and projections of cropland expansion. Suitability assessments typically consider edaphic conditions, climate, crop characteristics, and sometimes incorporate accessibility to transportation and market infrastructure. However, correct weighting among these disparate factors is challenging, given rapid development of new crop varieties, irrigation, and road networks, as well as changing global demand for agricultural commodities. Here, we compared three independent assessments of cropland suitability to spatial and temporal dynamics of agricultural expansion in the Brazilian state of Mato Grosso during 2001–2012. We found that areas of recent cropland expansion identified using satellite data were generally designated as low to moderate suitability for rainfed crop production. Our analysis highlighted the abrupt nature of suitability boundaries, rather than smooth gradients of agricultural potential, with little additional cropland expansion beyond the extent of the flattest areas (0–2% slope). Satellite-based estimates of the interannual variability in the use of existing crop areas also provided an alternate means to assess suitability. On average, cropland areas in the Cerrado biome had higher utilization (84%) than croplands in the Amazon region of northern Mato Grosso (74%). Areas of more recent expansion had lower utilization than croplands established before 2002, providing empirical evidence for lower suitability or alternative management strategies (e.g., pasture–soya rotations) for lands undergoing more recent land use transitions. This unplanted reserve constitutes a large area of potentially available cropland (PAC) without further expansion, within the management limits imposed for pest management and fallow cycles. Using two key constraints on future cropland expansion, slope and restrictions on further deforestation of Amazon or Cerrado vegetation, we found little available flat land for further legal expansion of crop production in Mato Grosso. Dynamics of cropland expansion from more than a decade of satellite observations indicated narrow ranges of suitability criteria, restricting PAC under current policy conditions, and emphasizing the advantages of field-scale information to assess suitability and utilization.  相似文献   

3.
Potential Soil C Sequestration on U.S. Agricultural Soils   总被引：1，自引：0，他引：1  
Soil carbon sequestration has been suggested as a means to help mitigate atmospheric CO2 increases, however there is limited knowledge aboutthe magnitude of the mitigation potential. Field studies across the U.S. provide information on soil C stock changes that result from changes in agricultural management. However, data from such studies are not readily extrapolated to changes at a national scale because soils, climate, and management regimes vary locally and regionally. We used a modified version of the Intergovernmental Panel on Climate Change (IPCC) soil organic C inventory method, together with the National Resources Inventory (NRI) and other data, to estimate agricultural soil C sequestration potential in the conterminous U.S. The IPCC method estimates soil C stock changes associated with changes in land use and/or land management practices. In the U.S., the NRI provides a detailed record of land use and management activities on agricultural land that can be used to implement the IPCC method. We analyzed potential soil C storage from increased adoption of no-till, decreased fallow operations, conversion of highly erodible land to grassland, and increased use of cover crops in annual cropping systems. The results represent potentials that do not explicitly consider the economic feasibility of proposed agricultural production changes, but provide an indication of the biophysical potential of soil C sequestration as a guide to policy makers. Our analysis suggests that U.S. cropland soils have the potential to increase sequestered soil C by an additional 60–70 Tg (1012g) C yr– 1, over present rates of 17 Tg C yr–1(estimated using the IPCC method), with widespread adoption of soil C sequestering management practices. Adoption of no-till on all currently annually cropped area (129Mha) would increase soil C sequestration by 47 Tg C yr–1. Alternatively, use of no-till on 50% of annual cropland, with reduced tillage practices on the other 50%, would sequester less – about37 Tg C yr–1. Elimination of summer fallow practices and conversionof highly erodible cropland to perennial grass cover could sequester around 20 and 28Tg C yr–1, respectively. The soil C sequestration potentialfrom including a winter cover crop on annual cropping systems was estimated at 40Tg C yr–1. All rates were estimated for a fifteen-yearprojection period, and annual rates of soil C accumulations would be expected to decrease substantially over longer time periods. The total sequestration potential we have estimated for the projection period (83 Tg C yr–1) represents about 5% of 1999total U.S. CO2 emissions or nearly double estimated CO2 emissionsfrom agricultural production (43 Tg C yr–1). For purposes ofstabilizing or reducing CO2 emissions, e.g., by 7% of 1990 levels asoriginally called for in the Kyoto Protocol, total potential soil C sequestration would represent 15% of that reduction level from projected 2008 emissions(2008 total greenhouse gas emissions less 93% of 1990 greenhouse gasemissions). Thus, our analysis suggests that agricultural soil C sequestration could play a meaningful, but not predominant, role in helping mitigate greenhouse gas increases.  相似文献   

4.
Previous research has demonstrated that soil carbon sequestration through adoption of conservation tillage can be economically profitable depending on the value of a carbon offset in a greenhouse gas (GHG) emissions market. However adoption of conservation tillage also influences two other potentially important factors, changes in soil N2O emissions and CO2 emissions attributed to changes in fuel use. In this article we evaluate the supply of GHG offsets associated with conservation tillage adoption for corn-soy-hay and wheat-pasture systems of the central United States, taking into account not only the amount of carbon sequestration but also the changes in soil N2O emission and CO2 emissions from fuel use in tillage operations. The changes in N2O emissions are derived from a meta-analysis of published studies, and changes in fuel use are based on USDA data. These are used to estimate changes in global warming potential (GWP) associated with adoption of no-till practices, and the changes in GWP are then used in an economic analysis of the potential supply of GHG offsets from the region. Simulation results demonstrate that taking N2O emissions into account could result in substantial underestimation of the potential for GHG mitigation in the central U.S. wheat pasture systems, and large over-estimation in the corn-soy-hay systems. Fuel use also has quantitatively important effects, although generally smaller than N2O. These findings suggest that it is important to incorporate these two effects in estimates of GHG offset potential from agricultural lands, as well as in the design of GHG offset contracts for more complete accounting of the effect that no-till adoption will have on greenhouse gas emissions.  相似文献   

5.
This study develops first-order estimates of water quality co-effects of terrestrial greenhouse gas (GHG) emission offset strategies in U.S. agriculture by linking a national level agricultural sector model (ASMGHG) to a national level water quality model (NWPCAM). The simulated policy scenario considers GHG mitigation incentive payments of $25 and $50 per tonne, carbon equivalent to landowners for reducing emissions or enhancing the sequestration of GHG through agricultural and land-use practices. ASMGHG projects that these GHG price incentives could induce widespread conversion of agricultural to forested lands, along with alteration of tillage practices, crop mix on land remaining in agriculture, and livestock management. This study focuses on changes in cropland use and management. The results indicate that through agricultural cropland about 60 to 70 million tonnes of carbon equivalent (MMTCE) emissions can be mitigated annually in the U.S. These responses also lead to a 2% increase in aggregate national water quality, with substantial variation across regions. Such GHG mitigation activities are found to reduce annual nitrogen loadings into the Gulf of Mexico by up to one half of the reduction goals established by the national Watershed Nutrient Task Force for addressing the hypoxia problem.  相似文献   

6.
Increasing carbon sequestration in agricultural soils in Canada is examined as a possible strategy in slowing or stopping the current increase in atmospheric CO2 concentrations. Estimates are provided on the amount of carbon that could be sequestered in soils in various regions in Canada by reducing summerfallow area, increased use of forage crops, improved erosion control, shifts from conventional to minimal and no-till, and more intensive use of fertilizers. The reduction of summerfallow by more intensive agriculture would increase the continuous cropland base by 8.1% in western Canada and 6.8% in all of Canada. Although increased organic carbon (OC) sequestration could be achieved in all agricultural regions, the greatest potential gains are in areas of Chernozemic soils. The best management options include reduction of summerfallow, conversion of fallow areas to hay or continuous cereals, fertilization to ensure nutrient balance, and adoption of soil conservation measures. The adoption of these options could sequester about 50-75% of the total agricultural emissions of CO2 in Canada for the next 30 years. However, increased sequestration of atmospheric carbon in the soil is possible for only a limited time. Increased efforts must be made to reduce emissions if long-term mitigation is to be achieved.  相似文献   

7.
The purpose of this paper is to develop and apply a new method to assess economic potential for agricultural greenhouse gas mitigation. This method uses secondary economic data and conventional econometric production models, combined with estimates of soil carbon stocks derived from biophysical simulation models such as Century, to construct economic simulation models that estimate economic potential for carbon sequestration. Using this method, simulations for the central United States show that reduction in fallow and conservation tillage adoption in the wheat-pasture system could generate up to about 1.7 million MgC/yr, whereas increased adoption of conservation tillage in the corn–soy–feed system could generate up to about 6.2 million MgC/yr at a price of $200/MgC. About half of this potential could be achieved at relatively low carbon prices (in the range of $50 per ton). The model used in this analysis produced estimates of economic potential for soil carbon sequestration potential similar to results produced by much more data-intensive, field-scale models, suggesting that this simpler, aggregate modeling approach can produce credible estimates of soil carbon sequestration potential. Carbon rates were found to vary substantially over the region. Using average carbon rates for the region, the model produced carbon sequestration estimates within about 10% of those based on county-specific carbon rates, suggesting that effects of spatial heterogeneity in carbon rates may average out over a large region such as the central United States. However, the average carbon rates produced large prediction errors for individual counties, showing that estimates of carbon rates do need to be matched to the spatial scale of analysis. Transaction costs were found to have a potentially important impact on soil carbon supply at low carbon prices, particularly when carbon rates are low, but this effect diminishes as carbon prices increase. This research was supported in part by the Montana State Agricultural Experiment Station, by the EPA STAR Climate Change program and by the Consortium for the Agricultural Mitigation of Greenhouse Gases. Although the research described in this article has been funded wholly or in part by the United States Environmental Protection Agency through grant R-82874501-0 to Montana State University, it has not been subjected to the Agency’s required peer and policy review and therefore does not necessarily reflect the views of the Agency and no official endorsement should be inferred.  相似文献   

8.
Afforestation of marginal agricultural lands represents a promising option for carbon sequestration in terrestrial ecosystems. An ecosystem carbon model was used to generate new national maps of annual net primary production (NPP), one each for continuous land covers of ‘forest’, ‘crop’, and ‘rangeland’ over the entire U. S. continental area. Direct inputs of satellite “greenness” data from the Advanced Very High Resolution Radiometer (AVHRR) sensor into the NASA-CASA carbon model at 8-km spatial resolution were used to estimate spatial variability in monthly NPP and potential biomass accumulation rates in a uniquely detailed manner. The model predictions of regrowth forest production lead to a conservative national projection of 0.3 Pg C as potential carbon stored each year on relatively low-production crop or rangeland areas. On a regional level, the top five states for total crop afforestation potential were: Texas, Minnesota, Iowa, Illinois, and Missouri, whereas the top five states for total rangeland afforestation potential are: Texas, California, Montana, New Mexico, and Colorado. Afforestation at this level of intensity has the capacity to offset at least one-fifth of annual fossil fuel emission of carbon in the United States. These projected afforestation carbon gains also match or exceed recent estimates of the annual sink for atmospheric CO2 in currently forested area of the country.  相似文献   

9.
Multiple cropping systems provide more harvest security for farmers, allow for crop intensification and furthermore influence ground cover, soil erosion, albedo, soil chemical properties, pest infestation and the carbon sequestration potential. We identify the traditional sequential cropping systems in ten sub-Saharan African countries from a survey dataset of more than 8600 households. We find that at least one sequential cropping system is traditionally used in 35% of all administrative units in the dataset, mainly including maize or groundnuts. We compare six different management scenarios and test their susceptibility as adaptation measure to climate change using the dynamic global vegetation model for managed land LPJmL. Aggregated mean crop yields in sub-Saharan Africa decrease by 6–24% due to climate change depending on the climate scenario and the management strategy. As an exception, some traditional sequential cropping systems in Kenya and South Africa gain by at least 25%. The crop yield decrease is typically weakest in sequential cropping systems and if farmers adapt the sowing date to changing climatic conditions. Crop calorific yields in single cropping systems only reach 40–55% of crop calorific yields obtained in sequential cropping systems at the end of the 21st century. The farmers’ choice of adequate crops, cropping systems and sowing dates can be an important adaptation strategy to climate change and these management options should be considered in climate change impact studies on agriculture.  相似文献   

10.
Net greenhouse gas (GHG) emissions from Canadian crop and livestock production were estimated for 1990, 1996 and 2001 and projected to 2008. Net emissions were also estimated for three scenarios (low (L), medium (M) and high (H)) of adoption of sink enhancing practices above the projected 2008 level. Carbon sequestration estimates were based on four sink-enhancing activities: conversion from conventional to zero tillage (ZT), reduced frequency of summerfallow (SF), the conversion of cropland to permanent cover crops (PC), and improved grazing land management (GM). GHG emissions were estimated with the Canadian Economic and Emissions Model for Agriculture (CEEMA). CEEMA estimates levels of production activities within the Canadian agriculture sector and calculates the emissions and removals associated with those levels of activities. The estimates indicate a decline in net emissions from 54 Tg CO2–Eq yr–1 in1990 to 52 Tg CO2–Eq yr–1 in 2008. Adoption of thesink-enhancing practices above the level projected for 2008 resulted in further declines in emissions to 48 Tg CO2–Eq yr–1 (L), 42 TgCO2–Eq yr–1 (M) or 36 Tg CO2–Eq yr–1 (H). Among thesink-enhancing practices, the conversion from conventional tillage to ZT provided the largest C sequestration potential and net reduction in GHG emissions among the scenarios. Although rates of C sequestration were generally higher for conversion of cropland to PC and adoption of improved GM, those scenarios involved smaller areas of land and therefore less C sequestration. Also, increased areas of PC were associated with an increase in livestock numbers and CH4 and N2O emissions from enteric fermentation andmanure, which partially offset the carbon sink. The CEEMA estimates indicate that soil C sinks are a viable option for achieving the UNFCCC objective of protecting and enhancing GHG sinks and reservoirs as a means of reducing GHG emissions (UNFCCC, 1992).  相似文献   

11.
Rates of soil C sequestration have previously been estimated for a number of different land management activities, and these estimates continue to improve as more data become available. The time over which active sequestration occurs may be referred to as the sequestration duration. Integrating soil C sequestration rates with durations provides estimates of potential change in soil C capacity and more accurate estimates of the potential to sequester C. In agronomic systems, changing from conventional plow tillage to no-till can increase soil C by an estimated 16±3%, whereas increasing rotation intensity can increase soil C by an estimated 6±3%. The increase in soil C following a change in rotation intensity, however, may occur over a slightly longer period (26 yr) than that for tillage cessation (21 yr). Sequestration strategies for grasslands have, on average, longer sequestration durations (33 yr) than for croplands. Estimates for sequestration rates and durations are mean values and can differ greatly between individual sites and management practices. As the annual sequestration rate declines over the sequestration duration period, soil C approaches a new steady state. Sequestration duration is synonymous with the time to which soil C steady state is reached. However, soils could potentially sequester additional C following additional changes in management until the maximum soil C capacity, or soil C saturation, is achieved. Carbon saturation of the soil mineral fraction is not well understood, nor is it readily evident. We provide evidence of soil C saturation and we discuss how the steady state C level and the level of soil C saturation together influence the rate and duration of C sequestration associated with changes in land management.  相似文献   

12.
Scientific interest in carbon sequestration on rangelands is largely driven by their extent, while the interest of ranchers in the United States centers on opportunities to enhance revenue streams. Rangelands cover approximately 30% of the earth's ice-free land surface and hold an equivalent amount of the world's terrestrial carbon. Rangelands are grasslands, shrublands, and savannas and cover 312 million hectares in the United States. On the arid and semi-arid sites typical of rangelands annual fluxes are small and unpredictable over time and space, varying primarily with precipitation, but also with soils and vegetation. There is broad scientific consensus that non-equilibrium ecological models better explain the dynamics of such rangelands than equilibrium models, yet current and proposed carbon sequestration policies and associated grazing management recommendations in the United States often do not incorporate this developing scientific understanding of rangeland dynamics. Carbon uptake on arid and semi-arid rangelands is most often controlled by abiotic factors not easily changed by management of grazing or vegetation. Additionality may be impossible to achieve consistently through management on rangelands near the more xeric end of a rangeland climatic gradient. This point is illustrated by a preliminary examination of efforts to develop voluntary cap and trade markets for carbon credits in the United States, and options including payment for ecosystem services or avoided conversion, and carbon taxation. A preliminary analysis focusing on cap and trade and payment for avoided conversion or ecosystem services illustrates the misalignment between policies targeting vegetation management for enhanced carbon uptake and non-equilibrium carbon dynamics on arid United States rangelands. It is possible that current proposed carbon policy as exemplified by carbon credit exchange or offsets will result in a net increase in emissions, as well as investment in failed management. Rather than focusing on annual fluxes, policy and management initiatives should seek long-term protection of rangelands and rangeland soils to conserve carbon, and a broader range of environmental and social benefits.  相似文献   

13.
Human land use contributes significantly to the growth of greenhouse gases in the atmosphere. Changes in land management practices have been proposed as a critical and cost-effective mechanism for reducing greenhouse gas emissions and promoting the storage of additional carbon in vegetation and soils. However many discussions of the potential for land use to mitigate climate change only take into account biophysical factors such as vegetation and land cover and neglect how the agency of land owners themselves affects whether additional carbon storage can be achieved. Unlike many potential REDD opportunities in developing countries, land management in the U.S. to enhance carbon sequestration would occur against a backdrop of clearly defined, legally enforceable land ownership. In addition, more than a third of the land surface in the U.S. is managed by federal agencies who operate under legal guidelines for multiple use and is subject to demands from multiple constituencies. We set out to investigate how the goal of enhancing carbon sequestration through land use is perceived or implemented in one region of the U.S., and how this goal might intersect the existing drivers and incentives for public and private land use decision making. We conducted a case study through interviews of the major categories of landowners in the state of Colorado, which represents a mixture of public and privately held lands. By analyzing trends in interview responses across categories, we found that managing for carbon is currently a fairly low priority and we identify several barriers to more widespread consideration of carbon as a management priority including competing objectives, limited resources, lack of information, negative perceptions of offsetting and lack of a sufficient policy signal. We suggest four avenues for enhancing the potential for carbon to be managed through land use including clarifying mandates for public lands, providing compelling incentives for private landowners, improving understanding of the co-benefits and tradeoffs of managing for carbon, and creating more usable science to support decision making.  相似文献   

14.
Carbon Sequestration and Turnover in Semiarid Savannas and Dry Forest   总被引：5，自引：1，他引：4  
Data on carbon and biomass budgets under different land use in tropical savannas and some dry forests are reviewed. Global data show wide ranges of biomass carbon stocks (20-150 Mg C ha-1), net primary production (2-15 Mg C ha-1y-1) and litter production (2-10 Mg C ha-1y-1) for the semiarid tropics. Although ranges for soil carbon are also wide, an average figure for the top 20 cm is probably 10 g C kg-1, or about 25 Mg C ha-1. In order to arrive at a better understanding of C budgets and their controls, two regional reviews are presented for NE Brazil and W. Africa.In NE Brazil approximately 40% of the lands have "near-climax" native vegetation. Less than 10% of the area is planted annually, but about 3-4 times that area is affected by shifting cultivation which has an average cycle of 5 y arable use followed by 20 y or more recovery. Standing biomass of native caatinga shows nearly the full global range with 2-50 Mg C ha-1. Litter fall around 1-2 Mg C ha-1y-1 is partly decomposed and partly consumed by animals, resulting in low average soil C levels near 8 g kg-1, or 20 Mg C ha-1. Under cultivation, C sequestration is decreased, and soils lose approximately half their C stocks before being abandoned.In W. Africa between 50-70% of the land is under a management regime with minimal C returns to the soils. Overgrazing and over-exploitation for fuel wood has resulted in land degradation. Short fallow periods on cultivated lands have caused serious declines in soil C stocks. Both C sequestration and stocks are therefore lower in W. Africa than in NE Brazil.Improvements in the C sequestration in these semi arid regions depend on an increase in crop production under suitable rotations, improved fallow and animal husbandry, and a limitation on biomnass burning. Use of fertilizer is required for improved productivities but socioeconomic constraints largely prevent such improvements, resulting in a very limited scope for changes in soil C management.  相似文献   

15.
Many savannas in West Africa have been converted to croplands and are among the world’s regions most vulnerable to climate change due to deteriorating soil quality. We focused on the savanna-derived cropland in northern Ghana to simulate its sensitivity to projected climate change and nitrogen fertilization scenarios. Here we show that progressive warming–drying stress over the twenty-first century will enhance soil carbon emissions from all kinds of lands of which the natural ecosystems will be more vulnerable to variation in climate variables, particularly in annual precipitation. The carbon emissions from all croplands, however, could be mitigated by applying nitrogen fertilizer at 30–60 kg N ha???1 year???1. The uncertainties of soil organic carbon budgets and crop yields depend mainly on the nitrogen fertilization rate during the first 40 years and then are dominated by climate drying stress. The replenishment of soil nutrients, especially of nitrogen through fertilization, could be one of the priority options for policy makers and farm managers as they evaluate mitigation and adaptation strategies of cropping systems and management practices to sustain agriculture and ensure food security under a changing climate.  相似文献   

16.
Understanding the magnitude of and uncertainty around soil carbon flux (SCF) is important in light of California’s efforts to increase SCF (from the atmosphere to soils) for climate change mitigation. SCF depends, to a great extent, on how soils are managed. Here, we summarize the results of an elicitation of soil science and carbon cycle experts aiming to characterize understanding of current SCF in California’s cropland and rangeland, and how it may respond to alternative management practices over time. We considered four cropland management practices—biochar, compost, cover crops, and no-till—and two rangeland management practices, compost and high-impact grazing. Results across all management practices reveal underlying uncertainties as well as very modest opportunities for soil carbon management to contribute meaningfully to California’s climate mitigation. Under median scenarios, experts expect all the surveyed management practices to reverse SCF from negative to positive, with direct carbon additions via biochar and compost offering the best potential for boosting the soil carbon pool.  相似文献   

17.
Carbon sequestration in agricultural soils is frequently promoted as a practical solution for slowing down the rate of increase of CO2 in the atmosphere. Consequently, there is a need to improve our understanding of how land management practices may affect the net removal of greenhouse gases (GHG) from the atmosphere. In this paper we examine the role of agriculture in influencing the GHG budget and briefly discuss the potential for carbon mitigation by agriculture. We also examine the opportunities that exist for increasing soil C sequestration using management practices such as reduced tillage, reduced frequency of summer fallowing, introduction of forage crops into crop rotations, conversion of cropland to grassland and nutrient addition via fertilization. In order to provide information on the impact of such management practices on the net GHG budget we ran simulations using CENTURY (a C model) and DNDC (a N model) for five locations across Canada, for a 30-yr time period. These simulations provide information on the potential trade-off between C sequestration and increased N2O emissions. Our model output suggests that conversion of cropland to grassland will result in the largest reduction in net GHG emissions, while nutrient additions via fertilizers will result in a small increase in GHG emissions. Simulations with the CENTURY model also indicated that favorable growing conditions during the last 15 yr could account for an increase of 6% in the soil C at a site in Lethbridge, Alberta. Presented at the International Workshop on Reducing Vulnerability of Agriculture and Forestry to Climate Variability and Climate Change, Ljubljana, Slovenia, 7–9 October 2002.  相似文献   

18.
This paper examines soil carbon sequestration in developing countries in sub-Saharan Africa as part of regional and global attempts to mitigate greenhouse gas emissions and the possibility that the development of greenhouse gas mitigation projects will offer local ancillary benefits. The paper documents the improvements in agricultural practices and land-use management in sub-Saharan Africa that could increase agricultural productivity and sequester soil carbon. During the first five-year commitment period of the Kyoto Protocol, only afforestation and reforestation projects will be eligible for crediting under the Clean Development Mechanism, but soil carbon sequestration and broader sink activities could become eligible during subsequent commitment periods. However, very few cost estimates of soil carbon sequestration strategies exist, and available data are not readily comparable. It is uncertain how large amounts of carbon could be sequestered, and it is unclear how well site-specific studies represent wider areas. It is concluded that there presently is a need to launch long-term (>10 years) field experiments and demonstration and pilot projects for soil carbon sequestration in Africa. It will be important to monitor all environmental effects and carbon `costs' as well as estimate all economic benefits and costs of projects.  相似文献   

19.
Designing effective mitigation policies for greenhouse gas (GHG) emissions from agriculture requires understanding the mechanisms by which management practices affect emissions in different agroclimatic conditions. Agricultural GHG emissions and carbon sequestration potentials have been extensively studied in the Mediterranean biome, which is a biodiversity hot spot that is highly vulnerable to environmental changes. However, the absolute magnitude of GHG emissions and the extent to which research efforts match these emissions in each production system, are unknown. Here, we estimated GHG emissions and potential carbon sinks associated with crop and livestock production systems in the Mediterranean biome, covering 31 countries and assessing approximately 10,000 emission items. The results were then combined with a bibliometric assessment of 797 research publications to compare emissions estimates obtained with research efforts for each of the studied items. Although the magnitude of GHG emissions from crop production and the associated carbon sequestration potential (261 Tg CO2eq yr−1) were nearly half of those from livestock production (367 Tg CO2eq yr−1), mitigation research efforts were largely focused on the former. As a result, the relative research intensity, which relates the number of publications to the magnitude of emissions, is nearly one order of magnitude higher for crop production than for livestock production (2.6 and 0.4 papers Tg CO2eq−1, respectively). Moreover, this mismatch is even higher when crop and livestock types are studied separately, which indicates major research gaps associated with grassland and many strategic crop types, such as fruit tree orchards, fiber crops, roots and tubers. Most life cycle assessment studies do not consider carbon sequestration, although this single process has the highest magnitude in terms of annual CO2eq. In addition, these studies employ Tier 1 IPCC factors, which are not suited for use in Mediterranean environments. Our analytical results show that a strategic plan is required to extend on-site field GHG measurements to the Mediterranean biome. Such a plan needs to be cocreated among stakeholders and should be based on refocusing research efforts to GHG balance components that have been afforded less attention. In addition, the outcomes of Mediterranean field studies should be integrated into life cycle assessment-based carbon footprint analyses in order to avoid misleading conclusions.  相似文献   

20.
Under the threat of global warming it is important to determine the impact that future changes in climate may have on the environment and to what extent any adverse effects can be mitigated. In this study we assessed the impact that climate change scenarios may have on soil carbon stocks in Canada and examined the potential for agricultural management practices to improve or maintain soil quality. Historical weather data from 1951 to 2001 indicated that semi-arid soils in western Canada have become warmer and dryer and air temperatures have increased during the spring and winter months. Results from the Canadian Center for Climate Modelling and Analysis (CCCma) Coupled Global Climate Model (CGCM1,2) under two climate change forcing scenarios also indicated that future temperatures would increase more in the spring and winter. Precipitation increased significantly under the IPCC IS92a scenario and agreed with historical trends in eastern Canada whereas the IPCC SRES B2 scenario indicated very little change in precipitation and better matched historical trends in western Canada. The Century model was used to examine the influence of climate change on agricultural soil carbon (C) stocks in Canada. Relative to simulations using historical weather data, model results under the SRES B2 climate scenario indicated that agricultural soils would lose 160 Tg of carbon by 2099 and under the IS92a scenario would lose 53 Tg C. Carbon was still lost from soils in humid climatic regions even though C inputs from crops increased by 10–13%. Carbon factors associated with changes in management practices were also estimated under both climate change scenarios. There was little difference in factors associated with conversion from conventional to no-till agriculture, while carbon factors associated with the conversion of annual crops to perennial grass were lower than for historical data in semi-arid soils because water stress hampered crop production but were higher in humid soils.  相似文献   

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