managing agricultural greenhouse gases || agriculture and climate change

CHAPTER 1

Agriculture and ClimateChange: MitigationOpportunities andAdaptation Imperatives
Mark A. Liebig1, Alan J. Franzluebbers2, Ronald F. Follett31USDA-ARS, Northern Great Plains Research Laboratory, Mandan, ND2USDA-ARS, J. Phil Campbell Sr., Natural Resource Conservation Center, Watkinsville, GA3USDA-ARS, Soil Plant Nutrient Research Unit, Ft. Collins, CO
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CHAPTER OUTLINE

Introduction 3Mitigating and Adapting To ClimateChange 5

Mitigation 6

anaging

012, Publ

Enhance Soil C Sequestration 6

Improve N-use Efficiency 6

Increase Ruminant Digestion

Efficiency 6

Capture GHG Emissions from Manure

and Other Wastes 6

Reduce Fuel Consumption 7

Agricultural Greenhouse Gases. DOI: 10.1016/B978-0-12-386897-8

ished by Elsevier Inc.

Adaptation 7

Increase Crop Diversity 7

Implement Efficient Irrigation

Methods 7

Adopt Integrated Pest Management

(IPM) 8

Improve Soil Management 8

Co-Benefits 8

Summary 9

NB: The U.S. Department of Agriculture, Agricultural Research Service is an equal opportunity/

affirmative action employer and all agency services are available without discrimination.

Abbreviations: C, carbon; CO2, carbon dioxide; CO2e, carbon dioxide equivalent;GWP, global warming potential; GRACEnet, Greenhouse gas Reduction through Agricultural

Carbon Enhancement Network; GHG, greenhouse gas; IPCC, Intergovernmental Panel onClimate Change; CH4, methane; N, nitrogen; N2O, nitrous oxide.

INTRODUCTIONCarbon (C) and nitrogen (N) are critically important elements for sustaining life on earth. The

balance of photosynthesis and respiration, along with methanotrophy and methanogenesis,

.00001-2

TABLE 1.1 Attribute

Species

Atmospconcentrat

(ppm;

CO2 38CH4 181N2O 32

yCO2 (ppm); CH4 and N2O (ppbzCapacity to trap heat in the at

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SECTION 1Agricultural Research for a Carbon-Constrained World

regulate the presence of C among the atmosphere, biomass, and soil. Nitrogen, as an integralpart of nucleotides and proteins, often limits net primary production (Schlesinger, 1997).

Accordingly, C and Ndand the key metabolic processes that regulate their transfer between

compartments in the biospheredaffect the production of food, feed, fiber, and fuel needed forour daily lives.

Carbon and N also play important roles in regulating environmental quality. Reactive forms ofboth elementsdwhen present in excess of biological requirementsdcan adversely impact

environmental quality across a range of spatial scales (Vitousek et al., 1997; Janzen, 2005).

Balancing concurrent needs of food security and a healthy environment is a crucial challengegiven projections for human population growth (Godfrey et al., 2010). As such, documenting

C and N dynamics within the biosphere will be essential to assess our relative success in

achieving these concurrent goals.

Agricultural production contributes to C and N dynamics through the flux of carbon dioxide

(CO2), methane (CH4,), and nitrous oxide (N2O), which represent the three greenhouse gases(GHG) principally associated with agricultural activities (Paustian et al., 2006). These three

GHGsdiffer considerably in their atmospheric concentration, residence time in the atmosphere,

globalwarming potential, and radiative forcing (Table 1.1). Carbondioxide, themost abundantof the three GHGs, is fixed by plants and a portion of it is respired back to the atmosphere.

Destruction of plant material through harvesting, natural decay, or burning also contributes to

CO2 emissions through microbial respiration and/or direct combustion. Agricultural-inducedfluxes of CH4 include emissions from ruminant livestock, flooded rice paddies, wetlands,

livestock manure, and burned biomass, and, conversely, uptake by methanotrophic bacteria in

soil under aerobic conditions. Fluxes of N2O from agriculture are typically unidirectionalthrough processes of nitrification or denitrification, with emissions most prevalent from

cultivated soils, livestock manure, and biomass burning (Schlesinger, 1997; Greenhouse Gas

Working Group, 2010; Climate Change Position Statement Working Group, 2011).

Agricultural contributions to total GHG emissions in the U.S. are relatively small, accounting

for approximately 6.3% of total emissions in 2009, or 419 of 6633 Tg CO2e yr�1 (U.S.-EPA,

2011). Of the three agricultural GHGs, emissions of CH4 and N2O are dominant, andconsidered in the U.S.-EPA Agriculture report exclusive of CO2 emissions and removals.

Methane emissions from enteric fermentation and manure management account for 96% ofthe total CH4 emissions from agriculture (189 Tg CO2e yr

�1), and are the second and fifth

largest anthropogenic sources of CH4 emissions in the U.S., respectively. Nitrous oxide

emissions from soil management practices make up 92% of agricultural N2O emissions(205 Tg CO2e yr

�1), and are by far the largest source of anthropogenic N2O emissions in the

U.S., accounting for 69% of the total. Emissions of CO2 from agriculture are largely

constrained to fossil fuel combustion, land conversion to cropland, lime application, and ureafertilization (S¼ 83.1 Tg CO2 yr

�1). However, agricultural practices in the U.S. sequester

approximately 49.3 Tg CO2 yr�1 through conversion of cropland to grassland, increased use

s of atmospheric CO2, CH4, and N2O (IPCC, 2007; NOAA, 2011)

hericion, 2009ppb)y

Residence timein atmosphere (yr)

Global warmingpotentialz

Global radiative forcing

2009 (W mL2)Increase since

1979 (W mL2; %)

7 5 1 1.760 0.734; 728 9 25 0.502 0.083; 203 120 298 0.173 0.074; 75

).

mosphere over a 100-year time horizon relative to CO2.

FIGURE 1.1Concentrations of atmospheric CO2, CH4, and N2O duringthe previous two millennia (after IPCC, 2007).

CHAPTER 1Agriculture and Climate Change

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of conservation tillage and continuous cropping, and improved management of organicfertilizers (U.S.-EPA, 2011).

Atmospheric concentrations of GHGs have increased significantly since the mid-1700s

(Figure 1.1). This increase has been driven mainly by fossil fuel combustion and land-usechange resulting from human activities. The capacity of GHGs to trap outgoing long-wave

radiation and emit it back to the earth’s surface as heat has contributed to global-scale climate

change (Paustian et al., 2006). Direct effects of climate change are significant and long-lasting,and include an increase in global average surface temperature, altered precipitation patterns,

reduced snow cover, increased sea level rise, and ocean acidification (IPCC, 2007). These

projected changes will have broad effects on agriculture (Follett, 2012). Shifts in vegetationzones, increased potential for droughts and floods, elevated rates of soil erosion, and increased

photosynthetic rates (from higher CO2 concentration) represent potential outcomes affectingagriculture, as well as how agriculture affects the broader environment (Climate Change

Position Statement Working Group, 2011; Janzen et al., 2011). Moreover, positive feedbacks

from climate changedsuch as accelerated soil organic matter decomposition and release ofCH4 from northern soilsdcould exacerbate such effects.

Challenges to agriculture associated with climate change are not short term. Momentum in

human population growth through the mid-21st century will almost surely result in increasedrates of GHG emissions, particularly from the energy sector (IPCC, 2007). Furthermore, even

if GHG emissions were to stabilize or decrease, consequences from global climate change

would continue well into the next century due to momentum from climate processes andfeedbacks (IPCC, 2007; Armour and Roe, 2011). This reality has led to an increased awareness

that agriculture has a crucial role to play in responding to climate change, both in miti-

gating its causes and adapting to its impacts (Climate Change Position Statement WorkingGroup, 2011).

MITIGATING AND ADAPTING TO CLIMATE CHANGERecent reviews have provided extensive lists documenting how agricultural practices canmitigate and/or adapt to climate change (CAST, 2011; Eagle et al., 2010; Greenhouse Gas

Working Group, 2010; Delgado et al., 2011; Lal et al., 2011; Climate Change Position Statement

Working Group, 2011). Broadly, suggested GHG mitigation practices either contribute to soilorganic C (SOC) accrual, reduce CH4 and/or N2O emissions, or reduce fuel consumption.

Adaptation responses to climate change address agroecosystem adjustments to alterations in

environmental conditions (Climate Change Position Statement Working Group, 2011). Suchresponses extend beyond regulating GHG fluxes through management, to address broader


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themes related to reducing negative impacts on agroecosystems while taking advantage ofpotential benefits associated with climate change.

Mitigation

The ASA-CSSA-SSSA Greenhouse Gas Working Group provided five broad strategies for

mitigating agricultural GHG emissions (Greenhouse Gas Working Group, 2010):

1. Enhance soil C sequestration;

2. Improve N-use efficiency;

3. Increase ruminant digestion efficiency;4. Capture GHG emissions from manure and other wastes; and

5. Reduce fuel consumption.

These five strategies are well established to either remove GHGs from the atmosphere (1) orreduce GHG emissions from known sources (2, 3, 4, 5). Because each mitigation strategy has

been thoroughly addressed in previous reviews, only a synopsis of each is provided here.

ENHANCE SOIL C SEQUESTRATION

Enhancement of soil C sequestration can be achieved bymaintaining plant residues on the soilsurface, minimizing soil disturbance and erosion, adopting complex cropping systems that

provide continuous ground cover, and applying C-rich substrates to soil (Lal and Follett,

2009). The magnitude and rate of soil C sequestration is dependent on various edaphic andclimatic factors that directly affect biomass productivity and C retention in soil (Brady and

Weil, 1999). In some instances, management practices have had variable effects on soil C

dynamics and CH4 and N2O flux, resulting in either enhancing (e.g. increased soil C, decreasedN2O emission) or negating (e.g. increased soil C, increased N2O emission) net GHG emis-

sions. Such variable responses emphasize the importance of inclusive GHG assessments to

ascertain GHG tradeoffs associated with management (Eagle et al., 2010).

IMPROVE N-USE EFFICIENCY

Improving N-use efficiency involves the implementation of management practices that makeN available in the amount needed at the correct time to meet plant demand (Lal et al., 2011).

When successful, such practices result in less reactive N available for potential conversion to

N2O. Numerous management practices are available to improve N-use efficiency, includinguse of legumes, cover crops, filter strips, and nitrification inhibitors, application of variable-

rate technology, and judicious use of soil tests to estimate soil N available for plant uptake

(Greenhouse Gas Working Group, 2010).

INCREASE RUMINANT DIGESTION EFFICIENCY

Methane emissions from ruminant livestock depend on many factors, most notably livestocktype, diet quality, and feed intake (Westberg et al., 2001). Strategies to reduce CH4 emissions

from livestock include improved feeding practices (e.g. enhancing pasture quality), use of

dietary amendments (e.g. edible oils, ionophores, organic acids), and improved genetics(Kebreab et al., 2006). However, the effectiveness of these strategies is often influenced by

environmental conditions, soil and plant interactions, animal behavior, and level of

management expertise (Murray et al., 2007).

CAPTURE GHG EMISSIONS FROM MANURE AND OTHER WASTES

Livestock manure can be a significant source of CH4 and N2O (U.S.-EPA, 2011). Capturingbiogas (CH4, CO2) from manure through anaerobic digestion increases production efficien-

cies by utilizing CH4 as fuel for generating on-site electricity and heat energy (Kebreab et al.,

2006). Moreover, residual solid material (sludge) following digestion may be used as fertilizer,thereby supplementing plant nutrient requirements. Additional strategies to reduce GHG


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fluxes from manure include composting, covering stored manure, altering diet composition,adoption of novel application methods, and using nitrification inhibitors (Kulling et al., 2001;

Schoenau et al., 2010).

REDUCE FUEL CONSUMPTION

Reduction in fuel consumption directly contributes to lower CO2 emissions. In this regard,

agricultural practices that reduce the number of field passes by farm machinery, such asconservation tillage, lower fuel consumption (West and Marland, 2002). Agricultural practices

that reduce applications of synthetic fertilizer and pesticides can reduce upstream CO2

emissions associated with their manufacture (Hoeppner et al., 2006). Additionally, imple-mentation of efficient irrigation practices (e.g. drip irrigation) and maximizing in-field grain

drying prior to harvest serves to increase energy-use efficiency, thereby avoiding CO2 emissions

(Greenhouse Gas Working Group, 2010).

Adaptation

Significant concerns exist regarding the capacity of agroecosystems to provide food, feed, fiber,

and fuel, and maintain ecosystem services under anticipated conditions of global climatechange. Development and adoption of adaptation strategies will be essential to minimize

negative biophysical and socioeconomic consequences, particularly as demand for agricultural

products and competition for natural resources increases with a larger human population(Tilman et al., 2011). While research on this topic is in its infancy, select management strategies

have been proposed to adapt to global climate change (Climate Change Position Statement

Working Group, 2011):

1. Increase crop diversity;

2. Implement efficient irrigation methods;3. Adopt integrated pest management; and

4. Improve soil management.

Each strategy directly or indirectly addresses adaptation to climate change by responding tochanges in long-term temperature and precipitation conditions, annual weather variation, and

challenges associated with invasive pests and/or diseases (Follett, 2012). Moreover, the strat-

egies serve to increase production efficiencies while simultaneously improving environmentalquality.

INCREASE CROP DIVERSITY

Increasing the number of crops in rotation as well as broadening the tolerance of crops to

drought, heat, and nutrient stresses through improved crop varieties can moderate weather-

related effects associated with climate change (Climate Change Position Statement WorkingGroup, 2011). Moreover, adoption of annual crop sequencing approaches that optimize

production, economic, and resource conservation goals can serve to increase management

adaptability in the context of climate-induced change (Hanson et al., 2007). Such croppingsystems, which are inherently dynamic in space and time, allow sequencing of crops in

a manner to take advantage of available water and nutrients while disrupting weed and disease

cycles (Tanaka et al., 2002). Accordingly, dynamic cropping systems can decrease requirementsfor off-farm inputs (e.g. fertilizer and pesticides) as compared with fixed-sequence and

monoculture cropping systems (Tanaka et al., 2005).

IMPLEMENT EFFICIENT IRRIGATION METHODS

Efficient utilization of water for crop growth will be essential in adapting to global climate

change. Irrigated agriculture is of particular concern, given its significant production potential

and high economic value relative to rainfed production systems, coupled with its vulnerabilityto depleted water supplies (Hatfield et al., 2011). Adoption of irrigation technology capable of


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delivering water to crops in space and time in precise doses with minimal loss will increasewater- and nutrient-use efficiency (Delgado et al., 2011). Additional strategies for efficient

water use include adoption of conservation practices that increase water storage and decrease

evaporative demand (Follett, 2012).

ADOPT INTEGRATED PEST MANAGEMENT (IPM)

Climate change has significant potential to increase the complexity of pest and disease

management. Anticipated effects of climate change include increased populations, shorter lifecycles, range expansion, increased herbivory, and new crop hosts (Chakraborty et al., 2000;

Bale et al., 2002). Implementation and/or modification of current IPM strategies will be

necessary to address these challenges, and will require the development of newmethodologiesto adapt IPM to different climatic conditions (Climate Change Position Statement Working

Group, 2011).

IMPROVE SOIL MANAGEMENT

Soil management practices that conserve water, minimize erosion, and improve soil functionwill contribute to increased agroecosystem resilience under anticipated climate change.

Generally, management strategies that increase C input to soil, reduce decay rates of soil

organic matter, and improve N-use efficiency will contribute positively to these improvementsin production efficiency (Eagle et al., 2010; Delgado et al., 2011; Lal et al., 2011; Follett, 2012).

Co-Benefits

Numerous management practices that mitigate GHG emissions or that can be used to adapt to

global climate change also enhance agroecosystem function, and accordingly contribute to theachievement of production and environmental goals (Lal and Follett, 2009; Delgado et al.,

2011; Lal et al., 2011). Such co-benefits have been strongly associated with practices that

enhance soil C sequestration (Janzen, 2005). Accrual of SOC in agricultural lands has beenassociated with improvements in soil physical, chemical, and biological properties, which

affect key soil functions, such as nutrient cycling, filtering and buffering capacity, and regu-

lation of hydrological attributes (Andrews et al., 2004; Franzluebbers, 2010). While preciserelationships are difficult to quantify, improvements in soil attributes and related functions

have positive effects on agronomic yield and environmental quality (Bauer and Black, 1994;

Diaz-Zorita et al., 1999; Wienhold et al., 2006; Lal and Follett, 2009). Such associations haveled others to assert that the greatest value from C sequestration may relate more to

improvements in soil functions, on-site productivity, and off-site environmental benefits than

a reduction in GHG emissions (Duxbury, 1994).

In many respects, mitigation and adaptation strategies focus on conserving C and N within

agroecosystems, thereby improving production efficiencies. Carbon and N retained in agro-

ecosystemsdand not lost through GHG emissionsdincreases the likelihood of more efficientuse of nutrients, water, energy, and labor, which can result in lower input costs for producers

(Delgado et al., 2011). Moreover, management strategies that directly reduce demands for

fossil energy and irrigation water translate to critically important economic co-benefits,particularly as these resources become more limiting, and hence more expensive (National

Intelligence Council, 2008).

In addition to economic co-benefits associated with improved production efficiencies, select

management practices may generate supplemental income for producers through payments

from emission trading programs. Such programs, similar to those previously administered bythe National Farmers Union (NFU) and Chicago Climate Exchange (CCX), have provided

a framework for GHG emitting entities (e.g. power generation companies) to offset their

emissions by purchasing credits from entities known to achieve net GHG uptake (Reicoskyet al., 2012). When active (2006e2010), the NFU/CCX program provided more than


$7 million in offset payments to U.S. farmers and ranchers employing conservation practicesknown to sequester atmospheric CO2 (Dale Enerson, personal communication, 2011). While

the future of such programs in the U.S. is unknown at this time, they have the potential to

provide valuable economic co-benefits for producers coping with agronomic impacts fromclimate change.

SUMMARYAtmospheric concentrations of GHGs have increased significantly since the mid-1700s. Thecapacity of GHGs to trap outgoing long-wave radiation and emit it back to the earth’s surface as

heat has contributed to global-scale climate change. Direct effects of climate change are

significant and long-lasting, and are projected to affect agriculture through shifts in vegetationzones, increased potential for droughts and floods, elevated rates of soil erosion, and increased

photosynthetic rates. Maintaining key agronomic and environmental functions in the future

will require deployment of a broad portfolio of management practices that can mitigate GHGemissions and/or adapt to impacts from climate change. Agricultural strategies for mitigating

GHG emissions include enhancing soil C sequestration, improving N-use efficiency, increasing

ruminant digestion efficiency, capturing GHG emissions from manure and other wastes, andreducing fuel consumption. Though less developed, climate change adaptation strategies

specific to agriculture include increasing crop diversity, implementing efficient irrigation

methods, adopting integrated pest management, and improving soil management. Significantproduction, environmental, and economic co-benefits potentially exist through the successful

application of mitigation and adaptation practices.

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managing agricultural greenhouse gases || agriculture and climate change

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