The purpose of this paper is to develop and apply a new method to assess economic potential for a... more 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
Agriculture, Ecosystems & Environment, Jun 1, 2016
Cattle play a major role in nutrient cycling of grassland ecosystems through biomass removal and ... more Cattle play a major role in nutrient cycling of grassland ecosystems through biomass removal and excrement deposition (urine and feces). We studied the effects of cattle excrement patches (urine at 430 and feces at 940 kg N ha -1 ) on nitrous oxide (N2O) and methane (CH4) fluxes using semi-static chambers on cool-season (C3), Bozoisky-select (Psathyrostachys juncea) pasture, and warm-season (C4)-dominated native rangeland of the shortgrass steppe (SGS) in northeastern Colorado. Nitrous oxide emission factors (EF; i.e., percent of added N emitted as N2O-N) did not differ between urine and feces on the C4-dominated native rangeland (0.11 and 0.10%) and C3 pasture (0.13 and 0.10%). These EFs are substantially less than the Intergovernmental Panel on Climate Change (IPCC) Tier 1 Default EF (2%) for manure deposited on pasture, indicating that during dry years the IPCC Tier 1 Default EF would result in a significant overestimation of emissions from excrement patches deposited on SGS C4dominated native rangeland and C3 pasture. Over the first year of the study (19 June 2012 to 18 June 2013), cumulative CH4 uptake was 38% greater for urine (-1.49 vs. -1.08 kg CH4-C ha -1 ) and 28% greater for control plots (-2.09 vs. -1.63 kg CH4-C ha -1 ) on C4-dominated native rangeland compared to C3 pasture. In contrast, feces patches were net sources of CH4 with emissions from the C3 pasture (0.64 kg CH4-C ha -1 ) 113% greater than the C4-dominated native rangeland (0.30 kg CH4-C ha -1 ). Conversion of C4-dominated native rangeland to C3 pasture can have long term effects on CH4 uptake; therefore consideration should be taken before implementing this management practice. Abbreviations: N2O, nitrous oxide; CH4, methane; EF, emission factor; GHG, greenhouse gas; SGS, shortgrass steppe; DOY, day of year; WFPS, water-filled pore space.
Agriculture, Ecosystems & Environment, Nov 1, 2011
We predicted changes in yields and direct net soil greenhouse gas (GHG) fluxes from converting co... more We predicted changes in yields and direct net soil greenhouse gas (GHG) fluxes from converting conventional to alternative management practices across one of the world's most productive agricultural regions, the Central Valley of California, using the DAYCENT model. Alternative practices included conservation tillage, winter cover cropping, manure application, a 25% reduction in N fertilizer input and combinations of these. Alternative practices were evaluated for all unique combinations of crop rotation, climate, and soil types for the period 1997-2006. The crops included were alfalfa, corn, cotton, melon, safflower, sunflower, tomato, and wheat. Our predictions indicate that, adopting alternative management practices would decrease yields up to 5%. Changes in modeled SOC and net soil GHG fluxes corresponded to values reported in the literature. Average potential reductions of net soil GHG fluxes with alternative practices ranged from -0.7 to -3.3 Mg CO 2 -eq ha -1 yr -1 in the Sacramento Valley and -0.5 to -2.5 Mg CO 2 -eq ha -1 yr -1 for the San Joaquin Valley. While adopting a single alternative practice led to modest net soil GHG flux reductions (on average -1 Mg CO 2 -eq ha -1 yr -1 ), combining two or more of these practices led to greater decreases in net soil GHG fluxes of up to -3 Mg CO 2 -eq ha -1 yr -1 . At the regional scale, the combination of winter cover cropping with manure application was particularly efficient in reducing GHG emissions. However, GHG mitigation potentials were mostly non-permanent because 60-80% of the decreases in net soil GHG fluxes were attributed to increases in SOC, except for the reduced fertilizer input practice, where reductions were mainly attributed to decreased N 2 O emissions. In conclusion, there are long-term GHG mitigation potentials within agriculture, but spatial and temporal aggregation will be necessary to reduce uncertainties around GHG emission reductions and the delivery risk of the associated C credits.
Changes in grassland management intended to increase productivity can lead to sequestration of su... more Changes in grassland management intended to increase productivity can lead to sequestration of substantial amounts of atmospheric C in soils. Managementintensive grazing (MiG) can increase forage production in mesic pastures, but potential impacts on soil C have not been evaluated. We sampled four pastures (to 50 cm depth) in Virginia, USA, under MiG and neighboring pastures that were extensively grazed or hayed to evaluate impacts of grazing management on total soil organic C and N pools, and soil C fractions. Total organic soil C averaged 8.4 Mg C ha -1 (22%) greater under MiG; differences were significant at three of the four sites examined while total soil N was greater for two sites. Surface (0-10 cm) particulate organic matter (POM) C increased at two sites; POM C for the entire depth increment (0-50 cm) did not differ significantly between grazing treatments at any of the sites. Mineral-associated C was related to silt plus clay content and tended to be greater under MiG. Neither soil C:N ratios, POM C, or POM C:total C ratios were accurate indicators of differences in total soil C between grazing treatments, though differences in total soil C between treatments attributable to changes in POM C (43%) were larger than expected based on POM C as a percentage of total C (24.5%). Soil C sequestration rates, estimated by calculating total organic soil C differences between treatments (assuming they arose from changing grazing management and can be achieved elsewhere) and dividing by duration of treatment, averaged 0.41 Mg C ha -1 year -1 across the four sites.
All supplemental information for McClelland et al. (2020). Management of cover crops in temperate... more All supplemental information for McClelland et al. (2020). Management of cover crops in temperate climates influences soil organic carbon stocks – A meta-analysis.
Soil carbon sequestration can contribute to greenhouse gas (GHG) mitigation by removing CO 2 from... more Soil carbon sequestration can contribute to greenhouse gas (GHG) mitigation by removing CO 2 from the atmosphere and at the same time improving soil health and sustainability. This article outlines the basic principles and controlling mechanisms involved in soil carbon sequestration and reviews how improved agricultural practices impact soil carbon stocks, based on data from long-term field experiments and other sources. It concludes with a section outlining challenges and opportunities for implementation of GHG mitigation strategies involving soil carbon sequestration, summarizing key science and policy-related issues.
Abstract CONTEXT Cover crops deliver numerous ecosystem services including the capacity to seques... more Abstract CONTEXT Cover crops deliver numerous ecosystem services including the capacity to sequester and store atmospheric CO2 offering promise as a natural climate solution. Farm system models must be able to accurately represent cover crop systems and estimate the associated net greenhouse gas emissions from this practice across agricultural contexts. OBJECTIVE The objectives of this study were to: (1) parameterize new and existing cover crop species for DayCent – the biogeochemical model behind the decisions-support tool, COMET-Farm – using published data on cover crop biomass production, (2) validate differences between cover crop and control systems using published and long-term data from across the U.S. for SOC and N2O emissions, and (3) evaluate model performance and discuss improvements to cover crop data reporting to facilitate future testing. METHODS We used published field experiment datasets from across the U.S. to estimate cover crop biomass production, SOC, and soil N2O emissions. We parameterized one new cover crop species in the model – sunn hemp (Crotalaria juncea L.) – and revised the parameters for existing model cover crop species using new biomass observations. We also validated the ability of the model to estimate changes in SOC and soil N2O emissions relative to a no cover crop control using empirical observations. RESULTS AND CONCLUSIONS For data sets used in parameterization, DayCent reasonably captured observed trends in aboveground biomass C, N, and C:N ratios across six different cover crop species and mixtures, explaining 25–69%, 14–58%, and 29–50% of the variation, respectively, with a few exceptions. Using a smaller validation dataset for a subset of these cover crop species – cereal rye (Secale cereale L.) and vetch (Vicia spp.) – the model demonstrated less agreement between modeled and observed aboveground biomass. For SOC model validation, the observed mean SOC difference between cover crop and control treatments was 178.4 g m−2 and the mean modeled difference was 158.2 g m−2. Observed soil N2O emissions were highly variable impacting model performance, but DayCent did capture the general trend from field measurements for cover crops to suppress soil N2O emissions. SIGNIFICANCE Our results demonstrate that even under limited data availability, process-based models like DayCent can inform on farm-scale biogeochemical processes under cover cropping. These findings are critical as cover crops are more widely adopted in the United States for their climate and environmental benefits. However, more detailed reporting from empirical studies will improve model estimates and reduce uncertainty, particularly data pertaining to farm management, soil, climate, and location.
... Title Modelling soil biology and biochemical processes for sustainable agriculture research. ... more ... Title Modelling soil biology and biochemical processes for sustainable agriculture research. Authors Paustian, K. Editors Pankhurst, CE;Doube, BM;Gupta, VVSR;Grace, PR Book Soil biota: management in sustainable farming systems. 1994 pp. ...
Journal of Soil and Water Conservation, Jul 1, 2002
ABSTRACT The exchange of carbon dioxide between the atmosphere, biosphere and pedosphere is an im... more ABSTRACT The exchange of carbon dioxide between the atmosphere, biosphere and pedosphere is an important consideration when assessing agricultural and environmental management or policy decisions and their relationship to climate change. Field experimentation is the best way to gather data, but experimental data are specific to the management, soils and climate that represent the research site. Inadequate field data exist to address all management options across all soil types and climates. We have used the Intergovernmental Panel on Climate Change inventory approach to estimate changes in soil carbon storage resulting from various land use and management options. We generate a regional assessment of the relative impact of implementing changes in agricultural management on soil carbon storage. For each agricultural region of the United States, we present an estimated annual change in soil carbon storage for each management option. Results should prove especially useful in evaluating management options and tradeoffs.
Currently, there is little information about soil organic carbon (SOC) stocks and changes in Medi... more Currently, there is little information about soil organic carbon (SOC) stocks and changes in Mediterranean areas at a regional scale. We modelled 9.5 Mha in northeast Spain using the Global Environmental Facility Soil Organic Carbon (GEFSOC) system to predict SOC stocks and changes in pasture, forest and agricultural soils. The spatial distribution of the different land use categories and their change over time was obtained by using the Corine database and official Spanish statistics on land use from 1926 to 2007. The model predicted the largest current SOC stock in forest soils at 578 Tg C. Agricultural soils were the second largest SOC reservoir containing 244 Tg C. During the last 30 years, the model predicted a total SOC gain in the 0-30 cm soil layer of 34 Tg C. Forest and grassland-pastures soils had a decline in their stored SOC by 5 and 3 Tg C, respectively, because the reduction in the soil surface occupied by both classes. The greatest SOC gain was predicted in agricultural soils with 42 Tg C caused by changes in management which led to increases in C inputs. Although model uncertainty was not quantified, some hypothetical assumptions on the initialization and parameterization of the model could be made of potential sources of uncertainty. Our simulations predicted that in northeast Spain soil management has contributed to the sequestration of substantial amounts of atmospheric CO 2 sinks during the last 30 years. More research is needed in order to study the potential role of soils as atmospheric CO 2 sinks under different managements and climatic conditions.
The purpose of this paper is to develop and apply a new method to assess economic potential for a... more 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
Agriculture, Ecosystems & Environment, Jun 1, 2016
Cattle play a major role in nutrient cycling of grassland ecosystems through biomass removal and ... more Cattle play a major role in nutrient cycling of grassland ecosystems through biomass removal and excrement deposition (urine and feces). We studied the effects of cattle excrement patches (urine at 430 and feces at 940 kg N ha -1 ) on nitrous oxide (N2O) and methane (CH4) fluxes using semi-static chambers on cool-season (C3), Bozoisky-select (Psathyrostachys juncea) pasture, and warm-season (C4)-dominated native rangeland of the shortgrass steppe (SGS) in northeastern Colorado. Nitrous oxide emission factors (EF; i.e., percent of added N emitted as N2O-N) did not differ between urine and feces on the C4-dominated native rangeland (0.11 and 0.10%) and C3 pasture (0.13 and 0.10%). These EFs are substantially less than the Intergovernmental Panel on Climate Change (IPCC) Tier 1 Default EF (2%) for manure deposited on pasture, indicating that during dry years the IPCC Tier 1 Default EF would result in a significant overestimation of emissions from excrement patches deposited on SGS C4dominated native rangeland and C3 pasture. Over the first year of the study (19 June 2012 to 18 June 2013), cumulative CH4 uptake was 38% greater for urine (-1.49 vs. -1.08 kg CH4-C ha -1 ) and 28% greater for control plots (-2.09 vs. -1.63 kg CH4-C ha -1 ) on C4-dominated native rangeland compared to C3 pasture. In contrast, feces patches were net sources of CH4 with emissions from the C3 pasture (0.64 kg CH4-C ha -1 ) 113% greater than the C4-dominated native rangeland (0.30 kg CH4-C ha -1 ). Conversion of C4-dominated native rangeland to C3 pasture can have long term effects on CH4 uptake; therefore consideration should be taken before implementing this management practice. Abbreviations: N2O, nitrous oxide; CH4, methane; EF, emission factor; GHG, greenhouse gas; SGS, shortgrass steppe; DOY, day of year; WFPS, water-filled pore space.
Agriculture, Ecosystems & Environment, Nov 1, 2011
We predicted changes in yields and direct net soil greenhouse gas (GHG) fluxes from converting co... more We predicted changes in yields and direct net soil greenhouse gas (GHG) fluxes from converting conventional to alternative management practices across one of the world's most productive agricultural regions, the Central Valley of California, using the DAYCENT model. Alternative practices included conservation tillage, winter cover cropping, manure application, a 25% reduction in N fertilizer input and combinations of these. Alternative practices were evaluated for all unique combinations of crop rotation, climate, and soil types for the period 1997-2006. The crops included were alfalfa, corn, cotton, melon, safflower, sunflower, tomato, and wheat. Our predictions indicate that, adopting alternative management practices would decrease yields up to 5%. Changes in modeled SOC and net soil GHG fluxes corresponded to values reported in the literature. Average potential reductions of net soil GHG fluxes with alternative practices ranged from -0.7 to -3.3 Mg CO 2 -eq ha -1 yr -1 in the Sacramento Valley and -0.5 to -2.5 Mg CO 2 -eq ha -1 yr -1 for the San Joaquin Valley. While adopting a single alternative practice led to modest net soil GHG flux reductions (on average -1 Mg CO 2 -eq ha -1 yr -1 ), combining two or more of these practices led to greater decreases in net soil GHG fluxes of up to -3 Mg CO 2 -eq ha -1 yr -1 . At the regional scale, the combination of winter cover cropping with manure application was particularly efficient in reducing GHG emissions. However, GHG mitigation potentials were mostly non-permanent because 60-80% of the decreases in net soil GHG fluxes were attributed to increases in SOC, except for the reduced fertilizer input practice, where reductions were mainly attributed to decreased N 2 O emissions. In conclusion, there are long-term GHG mitigation potentials within agriculture, but spatial and temporal aggregation will be necessary to reduce uncertainties around GHG emission reductions and the delivery risk of the associated C credits.
Changes in grassland management intended to increase productivity can lead to sequestration of su... more Changes in grassland management intended to increase productivity can lead to sequestration of substantial amounts of atmospheric C in soils. Managementintensive grazing (MiG) can increase forage production in mesic pastures, but potential impacts on soil C have not been evaluated. We sampled four pastures (to 50 cm depth) in Virginia, USA, under MiG and neighboring pastures that were extensively grazed or hayed to evaluate impacts of grazing management on total soil organic C and N pools, and soil C fractions. Total organic soil C averaged 8.4 Mg C ha -1 (22%) greater under MiG; differences were significant at three of the four sites examined while total soil N was greater for two sites. Surface (0-10 cm) particulate organic matter (POM) C increased at two sites; POM C for the entire depth increment (0-50 cm) did not differ significantly between grazing treatments at any of the sites. Mineral-associated C was related to silt plus clay content and tended to be greater under MiG. Neither soil C:N ratios, POM C, or POM C:total C ratios were accurate indicators of differences in total soil C between grazing treatments, though differences in total soil C between treatments attributable to changes in POM C (43%) were larger than expected based on POM C as a percentage of total C (24.5%). Soil C sequestration rates, estimated by calculating total organic soil C differences between treatments (assuming they arose from changing grazing management and can be achieved elsewhere) and dividing by duration of treatment, averaged 0.41 Mg C ha -1 year -1 across the four sites.
All supplemental information for McClelland et al. (2020). Management of cover crops in temperate... more All supplemental information for McClelland et al. (2020). Management of cover crops in temperate climates influences soil organic carbon stocks – A meta-analysis.
Soil carbon sequestration can contribute to greenhouse gas (GHG) mitigation by removing CO 2 from... more Soil carbon sequestration can contribute to greenhouse gas (GHG) mitigation by removing CO 2 from the atmosphere and at the same time improving soil health and sustainability. This article outlines the basic principles and controlling mechanisms involved in soil carbon sequestration and reviews how improved agricultural practices impact soil carbon stocks, based on data from long-term field experiments and other sources. It concludes with a section outlining challenges and opportunities for implementation of GHG mitigation strategies involving soil carbon sequestration, summarizing key science and policy-related issues.
Abstract CONTEXT Cover crops deliver numerous ecosystem services including the capacity to seques... more Abstract CONTEXT Cover crops deliver numerous ecosystem services including the capacity to sequester and store atmospheric CO2 offering promise as a natural climate solution. Farm system models must be able to accurately represent cover crop systems and estimate the associated net greenhouse gas emissions from this practice across agricultural contexts. OBJECTIVE The objectives of this study were to: (1) parameterize new and existing cover crop species for DayCent – the biogeochemical model behind the decisions-support tool, COMET-Farm – using published data on cover crop biomass production, (2) validate differences between cover crop and control systems using published and long-term data from across the U.S. for SOC and N2O emissions, and (3) evaluate model performance and discuss improvements to cover crop data reporting to facilitate future testing. METHODS We used published field experiment datasets from across the U.S. to estimate cover crop biomass production, SOC, and soil N2O emissions. We parameterized one new cover crop species in the model – sunn hemp (Crotalaria juncea L.) – and revised the parameters for existing model cover crop species using new biomass observations. We also validated the ability of the model to estimate changes in SOC and soil N2O emissions relative to a no cover crop control using empirical observations. RESULTS AND CONCLUSIONS For data sets used in parameterization, DayCent reasonably captured observed trends in aboveground biomass C, N, and C:N ratios across six different cover crop species and mixtures, explaining 25–69%, 14–58%, and 29–50% of the variation, respectively, with a few exceptions. Using a smaller validation dataset for a subset of these cover crop species – cereal rye (Secale cereale L.) and vetch (Vicia spp.) – the model demonstrated less agreement between modeled and observed aboveground biomass. For SOC model validation, the observed mean SOC difference between cover crop and control treatments was 178.4 g m−2 and the mean modeled difference was 158.2 g m−2. Observed soil N2O emissions were highly variable impacting model performance, but DayCent did capture the general trend from field measurements for cover crops to suppress soil N2O emissions. SIGNIFICANCE Our results demonstrate that even under limited data availability, process-based models like DayCent can inform on farm-scale biogeochemical processes under cover cropping. These findings are critical as cover crops are more widely adopted in the United States for their climate and environmental benefits. However, more detailed reporting from empirical studies will improve model estimates and reduce uncertainty, particularly data pertaining to farm management, soil, climate, and location.
... Title Modelling soil biology and biochemical processes for sustainable agriculture research. ... more ... Title Modelling soil biology and biochemical processes for sustainable agriculture research. Authors Paustian, K. Editors Pankhurst, CE;Doube, BM;Gupta, VVSR;Grace, PR Book Soil biota: management in sustainable farming systems. 1994 pp. ...
Journal of Soil and Water Conservation, Jul 1, 2002
ABSTRACT The exchange of carbon dioxide between the atmosphere, biosphere and pedosphere is an im... more ABSTRACT The exchange of carbon dioxide between the atmosphere, biosphere and pedosphere is an important consideration when assessing agricultural and environmental management or policy decisions and their relationship to climate change. Field experimentation is the best way to gather data, but experimental data are specific to the management, soils and climate that represent the research site. Inadequate field data exist to address all management options across all soil types and climates. We have used the Intergovernmental Panel on Climate Change inventory approach to estimate changes in soil carbon storage resulting from various land use and management options. We generate a regional assessment of the relative impact of implementing changes in agricultural management on soil carbon storage. For each agricultural region of the United States, we present an estimated annual change in soil carbon storage for each management option. Results should prove especially useful in evaluating management options and tradeoffs.
Currently, there is little information about soil organic carbon (SOC) stocks and changes in Medi... more Currently, there is little information about soil organic carbon (SOC) stocks and changes in Mediterranean areas at a regional scale. We modelled 9.5 Mha in northeast Spain using the Global Environmental Facility Soil Organic Carbon (GEFSOC) system to predict SOC stocks and changes in pasture, forest and agricultural soils. The spatial distribution of the different land use categories and their change over time was obtained by using the Corine database and official Spanish statistics on land use from 1926 to 2007. The model predicted the largest current SOC stock in forest soils at 578 Tg C. Agricultural soils were the second largest SOC reservoir containing 244 Tg C. During the last 30 years, the model predicted a total SOC gain in the 0-30 cm soil layer of 34 Tg C. Forest and grassland-pastures soils had a decline in their stored SOC by 5 and 3 Tg C, respectively, because the reduction in the soil surface occupied by both classes. The greatest SOC gain was predicted in agricultural soils with 42 Tg C caused by changes in management which led to increases in C inputs. Although model uncertainty was not quantified, some hypothetical assumptions on the initialization and parameterization of the model could be made of potential sources of uncertainty. Our simulations predicted that in northeast Spain soil management has contributed to the sequestration of substantial amounts of atmospheric CO 2 sinks during the last 30 years. More research is needed in order to study the potential role of soils as atmospheric CO 2 sinks under different managements and climatic conditions.
Uploads
Papers by Keith Paustian