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MITIGATION AND ADAPTATION POTENTIAL OF
SUSTAINABLE FARMING SYSTEMS
LOW
GREENHOUSE GAS
AGRICULTURE
Niggli, U., Fließbach, A., Hepperly, P. and Scialabba, N. 2009. Low Greenhouse Gas Agriculture: Mitigation
and Adaptation Potential of Sustainable Farming Systems. FAO, April 2009, Rev. 2 – 2009.
Research Institute of Organic Agriculture (FiBL): www.fibl.org
The Rodale Institute, USA: www.rodaleinstitute.org
FAO, Natural Resources Management and Environment Department: www.fao.org/organicag
This document was first published in May 2008, on the occasion of the High-Level Conference on World
Food Security: The Challenges of Climate Change and Bioenergy, Rome, 3-5 June 2008. This revised
version is issued in April 2009.
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MITIGATION AND ADAPTATION POTENTIAL OF
SUSTAINABLE FARMING SYSTEMS
LOW
GREENHOUSE GAS
AGRICULTURE
CONTENTS
Introduction
Mitigation options of agricultural
practices and techniques
Is a low greenhouse gas emission agriculture possible?
The potential of ecologically managed farmsto adapt to
climate change
Conclusions
References
1
1
11
14
16
17
List of tables and figures
Table 1
Global nitrogen input and nitrogen circuits in agriculture
Table 2
Input and output of organic and integrated farming systems
of the DOK trial
Table 3
Above ground net primary production and relative
Global Warming Potential
Table 4
Comparison of soil carbon gains and losses in different
farming systems in long term field experiments
Figure 1
Agricultural emissionons and mitigation potential
4
5
7
10
13
LOW GREENHOUSE GAS AGRICULTURE: MITIGATION AND ADAPTATION POTENTIAL OF SUSTAINABLE FARMING SYSTEMS
1
INTRODUCTION
Is low greenhouse gas emission (GHG) agriculture possible? Is it, in fact, desirable?
In seeking answers to these two basic but extremely relevant questions, this study
examines current farming practices, and incorporates scientific databases from long-
term field experiments as case studies for low GHG agriculture. Further, the study
examines the changes that will be needed for low greenhouse gas agriculture systems
to become a reality. It also elucidates the adaptive capacity of agro-ecological farming
system approaches, using organic system case studies from the scientific literature.
Each year, agriculture emits 10 to 12 percent of the total estimated GHG emissions,
some 5.1 to 6.1 Gt CO2 equivalents per year. Smith, et al. (2007) and Bellarby, et al. (2008)
have proposed mitigation options for GHG emissions, finding that both farmers and policy-
makers will face challenges from the GHG-related changes needed in agriculture. Areas
for improvement include increased use of no-till cropping, agro-forestry, and integrated
crop and animal farming, and decreased use of external inputs in food and agriculture. The
techniques offered by organic agriculture are valuable for consideration in these efforts.
MITIGATION OPTIONS OF AGRICULTURAL
PRACTICES AND TECHNIQUES
The Fourth Assessment Report of the Intergovernmental Panel on Climate Change
(IPCC) made important recommendations on how agriculture could mitigate GHG
emissions (Smith, et al., 2007).
This report summarizes these recommendations (in the four sections below) and
then compares them to scientific data from organic agriculture in order to assess the
mitigation potential of organic farming. The four major recommendations include:
crop rotations and farming system design; nutrient and manure management;
livestock management; pasture and fodder supply improvement; fertile soil fertile soil
maintenance and restoration of degraded land.
Crop rotations and farming system design
IPCC Fourth Assessment Report recommended:
o
improve crop varieties,
o
feature perennials in crop rotations,
o
use cover crops (between successive crops or between rows of plantations) and
avoid bare fallows,
o
enhance plant and animal productivity and efficiency,
o
adopt farming systems with reduced reliance on external inputs (e.g. rotations
which include legume crops).
2
LOW GREENHOUSE GAS AGRICULTURE: MITIGATION AND ADAPTATION POTENTIAL OF SUSTAINABLE FARMING SYSTEMS
Two of organic agricultures current priorities – improving crop and animal
productivity under low-external-input environments and selecting varieties and
breeds especially fit for these conditions – can cope with several of the above-
mentioned recommendations simultaneously. NUE-CROPS, a new EU Framework
Programme for Research and Technological Development (FP7) project, addresses
crop breeding with the goal of identifying nutrient- efficient varieties of wheat,
potatoes, maize, and oilseed rape. It also will study the combined effects of genotype
and management practices on nutrient use efficiency, with a special emphasis on
reduced tillage organic farming. Most recent genetic studies on maize and wheat
have shown that selecting under organic and low-external-input agriculture can
improve yields and yield stability considerably (Burger, et al., 2008; Löschenberger,
et al., 2008). Another EU project, LowInputBreed, began in spring 2009 with aims
of better exploiting effects of interactions of genotype and environment on genetic
gain in breeding programs in organic and low input livestock systems.
Intensive crop production (often based on monocultures and high productivity)
depends greatly on external inputs such as mineral fertilizers and pesticides.
Sustainable agricultural practices, such as organic agriculture, strongly reduce the
reliance on external inputs by:
o
recycling wastes as nutrient source,
o
using nitrogen-fixing plants,
o
improving cropping systems and landscapes,
o
avoiding synthetic pesticides,
o
integrating crops and animals into a single farm production sector and including grass
clover leys for fodder production, while avoiding purchase of feed concentrates.
In order to avoid nutrient losses, especially since nutrients are limited in low-input
systems, soils should be covered permanently by crops in an optimized sequence. In organic
agriculture, the inclusion of cover and catch crops is both a traditional and state-of-the-art
practice (Thorup-Kristensen, et al., 2003). Bare fallows are not only unproductive, they are
more prone to nutrient loss. As purchased organic fertilizers are expensive, organic farmers
have not only environmental reasons to avoid losses, but also economic incentives.
Nutrients for sustainable crop production can be delivered by soil transformation
through application of manure or compost or fixed by leguminous plants. Nitrogen (N)
from legumes is more sustainable in terms of ecological integrity, energy flows and food
security than nitrogen from industrial sources (Crews and Peoples, 2004). These nutrients are
partly biologically bound and have to be mineralized by soil microbiological processes.
Productivity in sustainable agriculture is enhanced by many indirect measures
based on improving soil fertility and stimulating the roles of plants and microbes
in natural soil processes. The role of soil carbon is pre-eminent. It is important for
soil moisture while also contributing to counteracting greenhouse gases. Such soil
processes driven productivity gains are typical for organic farming:
LOW GREENHOUSE GAS AGRICULTURE: MITIGATION AND ADAPTATION POTENTIAL OF SUSTAINABLE FARMING SYSTEMS
3
Mycorrhizal fungi are practically important in carbon sequestration and mineral
solubilization. Intercropping and under-sowing legumes as well as combining
deep and shallow rooting crops provide other approaches to increase productivity
and nutrient efficiency internally through nitrogen resource management. Needed
nitrogen can be supplied using both symbiotic and non-symbiotic nitrogen fixation
and exploiting soil phosphorus and water resources by symbiotic mycorrhiza (Mäder,
et al., 2000; 2002). Integrated crop and animal farming and cooperation between
specialized farms are a basis for recycling animal faeces and diversifying production
sectors, especially due to crop and fodder diversity and grass-clover leys.
Nutrient and manure management
IPCC Fourth Assessment Report recommended:
o
improve nitrogen-use efficiency (reducing leaching and volatilization, reducing
offsite N2O emissions),
o
adjust fertilizer application to crop needs (synchronization),
o
use slow-release fertilizers,
o
apply N when crop uptake is guaranteed,
o
place N into soil to enhance accessibility,
o
avoid any surplus-N applications,
o
manage tillage and residues conservatively,
o
reduce unnecessary tillage using minimum and no-till strategies.
In agro-ecosystems, mineral nitrogen in soils is the driver of crop productivity in many
cases. Crop productivity has increased substantially through utilization of heavy inputs of
soluble fertilizers – mainly nitrogen – and synthetic pesticides. However, only 17 percent
of the 100 Mt N produced in 2005 was taken up by crops. The remainder was somehow
lost to the environment (Erisman, et al., 2008). Between 1960 and 2000, the efficiency of
nitrogen use for cereal production decreased from 80 to 30 percent (Erisman, et al., 2008)
High levels of reactive nitrogen (NH4, NO3) in soils may contribute to the emission
of nitrous oxides and are main drivers of agricultural emissions. The efficiency
of fertilizer use decreases with increasing fertilization, because a great part of the
fertilizer is not taken up by the plant but instead emitted into the water bodies and the
atmosphere. In summary, the emission of GHG in CO2 equivalents from the production
and application of nitrogen fertilizers from fossil fuel amounted to 750 to 1080 million
tonnes (1 to 2 percent of total global GHG emissions) in 2007. In 1960, 47 years earlier,
it was less than 100 million tonnes.
Recycling nitrogen on the farm by using manure and nitrogen fixing plants
enhances soil quality and provides nutrients. This is the predominant technique of
organic and low external input agriculture. However, timing and management of
4
LOW GREENHOUSE GAS AGRICULTURE: MITIGATION AND ADAPTATION POTENTIAL OF SUSTAINABLE FARMING SYSTEMS
its use are essential. Soil mineralization processes should deliver the elements to
the plant at times of peak demand. Organic and green manures as well as nitrogen
from legumes can be managed very precisely due to the design of the crop rotations
including cover and catch crops (Thorup-Kristensen, et al., 2003). In addition,
improved distribution systems, such as slurry injections into soils or drag hoses,
reduce nutrients losses considerably. All these techniques might be knowledge-
intensive for farmers and require site specific adaptations. As nitrogen on organic
farms is far more costly than industrial nitrogen, there is a strong incentive to avoid
losses and to learn and implement recycling techniques (Stolze, et al., 2000).
The global potential of nitrogen availability through recycling and nitrogen
fixation is far bigger than the current production of synthetic nitrogen, as shown
Table 1. On-farm use of farmyard manure (a practice increasingly abandoned in
conventional production) needs to be reconsidered in the light of climate change.
While conventional stockless arable farms become dependent on the input of
synthetic nitrogen fertilizers, manure and slurry from livestock farms become an
environmental problem. In these livestock operations, nutrients are available in
excess and over-fertilization may occur. Nutrient leaching leads to water pollution
and high emissions of carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4)
are likely. The concept of either mixed farms or close cooperation between crop and
livestock operations – a common practice of most forms of sustainable farming,
especially organic ones – can contribute considerably to mitigation and adaptation.
In addition, different forms of compost, especially composted manure, are particularly
useful in stimulating soil microbial processes and in building up stable forms of the
soil organic matter (Fließbach and Mäder, 2000).
Table 1
Global nitrogen input and nitrogen circuits in agriculture
Nitrogen derived from industrial production
(by the Haber-Bosch process with fossil fuel combustion)
90 to 100 Mt N
per year
Erisman, et al.,
2008, IFA, 2009
Potential nitrogen production by leguminous plants via
intercropping and off-season cropping (without competing
cash crops). This potential is not used by conventional farmers.
140 Mt N
per year
Badgley, et al.,
2007
Nitrogen from livestock faeces of 18.3 billion farm animalsof 18.3 billion farm animals
(FAO, global figure). In specialized farming structure with
strong segregation between crop and livestock production,
nitrogen from manure and slurry is inefficiently used.
160 Mt N
per year
Estimated by
the authors
Farming systems with ecological objectives either limit the amount of fertilizer
use (such as in integrated farming) and/or limit livestock numbers per area or the
LOW GREENHOUSE GAS AGRICULTURE: MITIGATION AND ADAPTATION POTENTIAL OF SUSTAINABLE FARMING SYSTEMS
5
purchase of fodder (such as in organic agriculture), thus limiting the return of
nitrogen and other elements to the soil. N-application rates in organic agriculture
are usually 60 to 70 percent lower than in conventional agriculture because of the
recycling of organic residues and manures. In addition, the limited availability of
nitrogen in organic systems requires careful, efficient management (Kramer, et al.,
2006), as shown in Table 2.
Table 2
Input and output of organic and integrated farming systems of the DOK trial
DOK LONG-TERM FIELD TRIAL IN THERWIL SWITZERLAND (DATA FOR THE YEARS 1977 TO 2005)
Parameter Unit Organic farming Integrated farming
(IP) with FYM
Organic in %
of IP
Nutrient
input
kg Ntotal ha-1 yr-1 101 157 64
kg Nmin ha-1 yr-1 34 112 30
kg P ha-1 yr-1 25 40 62
Pesticides
applied
kg K ha-1 yr-1 162 254 64
kg ha-1 yr-1 1.5 42 4
Fuel use L ha-1 yr-1 808 924 87
Total yield output
for 28 years % 83 100 83
Soil microbial
biomass „output“ tons ha-1 40 24 167
(source: Mäder, et al., 2006)
Input of nutrients, organic matter, pesticides and energy as well as yields were calculated on the
basis of 28 years. Crop sequence was potatoes, winter wheat followed by fodder intercrop, vegetables
(soybean), winter wheat (maize), winter barley (grass-clover for fodder production, winter wheat),
grass-clover for fodder production, grass-clover for fodder production. Crops in brackets are alterations
in 1 of the 4 crop rotations.
Pimentel, et al. (2005) report yields in organic maize and soybean are comparable
to conventional maize and soybean production. Depending on the environment, this
indicates that organic field crop production can be competitive with conventional
farming even in a high-yield environment.
Mäder, et al. (2002) report an increased efficiency of input use of organic
agriculture,, with crop yield reduction of less than 20 percent while fertilizer inputs
were lower by 50 to 60 percent (Table 2).
In life cycle assessments, Nemecek, et al. (2005) showed that area-based GHG
emissions in the organic systems were 36 percent lower than in conventional
6
LOW GREENHOUSE GAS AGRICULTURE: MITIGATION AND ADAPTATION POTENTIAL OF SUSTAINABLE FARMING SYSTEMS
systems. Per kg product, the GHG emissions were 18 percent lower due to 22 percent
lower dry matter yields (Table 2). Most of this difference was caused by CO2 and
N2O emissions – both of which are mainly related to mineral fertilizer use in
conventional farming.
Benchmarking: GHG emissions per land area or per product quantity?
Environmental concern – such as nitrate losses into groundwater or
biodiversity loss through over-fertilization and overgrazing – is the
main rationale behind organic agriculture standards on stocking density,
limiting livestock to two units per ha in most productive areas. Animal
welfare is another reason, because lower stocking densities offer free
movement to animals. Therefore, the very purpose of the organic
paradigm is producing less livestock while increasing the share of crops
for human consumption. In this respect, per area benchmarking of GHG
emissions is more appropriate than per product quantity for farming
system comparisons, especially in the context of climate change and
livestock production.
In organic agriculture, the ban of mineral nitrogen and the reduced livestock
units per ha considerably decrease the concentration of easily available mineral
nitrogen in soils and, thus, N2O emissions. Furthermore, diversifying crop rotations
with green manure improves soil structure and diminishes N2O emissions. Soils
managed organically are more aerated and have significantly lower mobile nitrogen
concentrations, which further reduces N2O emissions. Mathieu, et al. (2006) pointed
out that higher soil carbon levels may lead to N2 emission rather than N2O. Petersen,
et al. (2006) found lower emission rates for organic farming compared to conventional
farming in five European countries. In a long-term study in southern Germany,
Flessa, et al. (2002) also found reduced N2O emission rates in organic agriculture,
although yield-related emissions were not reduced.
A reduction of the Global Warming Potential (GWP) has also been found on Dutch
organic dairy farms and in organic pea production areas as compared to conventional
(Bos, et al. 2006). In contrast, the authors found higher GHG emissions for organic
vegetable crops (e.g. leek and potato). In other studies, organic potatoes, tomatoes,
and various other vegetables (Öko-Institut, 2007) had less GHG emissions than the
compared conventional crops. In contrast, higher emissions for organic crops were
found in the experimental farm in Scheyern (Bavaria), Germany (Küstermann, et al.
2007). The authors also calculated the GHG emissions of 28 Bavarian commercial
crop farms – organic and conventional – and found equal and, in some cases, slightly
higher emissions for organic.
LOW GREENHOUSE GAS AGRICULTURE: MITIGATION AND ADAPTATION POTENTIAL OF SUSTAINABLE FARMING SYSTEMS
7
Table 3
Above ground net primary production and relative Global Warming Potential
Net primary
production
[kg ha-1 yr-1]
C-sequestration
[kg CO2-eq ha-1 yr-1]
Net global warming
potential
[kg CO2-eq ha-1 yr-1]
Net global warming
potential per NPP
[kg CO2-eq ton-1]
Conventional
tillage 9240 0 1140 100% 123.38 100%
No till 9190 1100 140 12% 15.23 12%
Low input
with legume
cover
8840 400 63030 55% 71.27 58%
Organic with
legume cover 7790 290 410 36% 52.63 43%
(source: Robertson et al., 2000)
These figures demonstrate how crucial it is to choose the right data base, to apply
the right model and to define system boundaries properly. When carbon sequestration
was excluded from life cycle assessments on the Scheyern experimental farm, the
GWP was 53 percent higher in the organic system compared to conventional,
but was 80 percent lower when carbon sequestration was included (Küstermann,
et al., 2007). In a Michigan State University study, Robertson, et al. (2000) calculated
that net GWP for organic systems was 64 percent lower than conventional systems
(Table 3). Due to 16 percent lower net primary productivity, the GWP on a product
basis was 57 percent lower in organic than in conventional.
Reduced tillage techniques, increasingly and successfully applied to organic systems
(Berner, et al., 2008; Teasdale, et al., 2007), enhance carbon sequestration rates
considerably (see Table 4). Contrary to conventional no-till systems, organic reduced
tillage systems do not increase herbicide and synthetic nitrogen input.
Livestock management, pasture and fodder supply improvement
IPCC Fourth Assessment Report recommended:
o
reduce lifetime emissions,
o
breed dairy cattle for lifetime efficiency,
o
breed and manage to increase productivity,
o
plant deep-rooting species in primary production,
o
introduce legumes into grasslands (to enhance productivity),
o
prevent methane emissions from manure heaps and tanks,
o
utilize biogas as a resource,
o
compost manure.
8
LOW GREENHOUSE GAS AGRICULTURE: MITIGATION AND ADAPTATION POTENTIAL OF SUSTAINABLE FARMING SYSTEMS
Methane accounts for about 14 percent of all greenhouse gas emissions (Barker, et al.,
2007). Two thirds of the methane emissions stem from enteric fermentation and manure
management and, as a consequence, are directly proportional to livestock numbers.
On most organic farms, crop and livestock production are closely linked to
traditional mixed farms or by regional cooperation of specialized farms or farm
branches. This leads to lower input of nutrients by farmyard manure (FYM) on
grassland and pastures as well as to fewer environmental problems such as
phosphorous run-off, nitrogen leaching into deeper soil layers and emission of N2O.
Organic agriculture has an important, though not always superior, impact on the
reduction of N2O, because organic has limited livestock numbers (Weiske, et al.,
2006; Olesen, et al., 2006).
As a result of moderate fertilization, grassland and pastures tend to be more
diverse on organic farms. Typically on organic farms, the diverse grassland species
reach different soil layers in order to improve exploitation of soil nutrients. Legumes
are strongly promoted on organic grasslands and pastures, as they increase nitrogen
uptake into the soil and provide protein into the feedstuff.
The data available on methane emissions from livestock is limited, especially
with respect to the reduction of GHG emissions from ruminants and manure heaps.
Some authors recommend high-energy feedstuff to reduce methane emissions from
ruminants (Beauchemin and McGinn, 2005), but the ruminants’ unique ability
to digest roughage from pastures would then not be used. Furthermore, meat
and milk would be produced with feed concentrates produced in remote arable
lands, which make intensive use of mineral nitrogen (an important CO2 emitter),
and which use crops for feed rather than for food, with the attendant human
nutrition implications.
Another positive difference between organic and conventional cattle husbandry
is that organic breeders aim at longevity (Kotschi and Müller-Sämann, 2004). The
ratio between the unproductive phase of young cattle and the productive phase of
dairy cows is favourable in organic systems because, calculated on the basis of the
total lifespan of organic dairy cows, less methane is emitted. On the other hand,
lower milk yields of organic cows caused by a higher proportion of roughage in the
diet, might increase methane emissions per yield unit.
Storage and composting of manure and organic waste have been strongly
improved on organic farms in recent years. Using the modern techniques, such as
covering, processing compost and steering the compost process, prevents leaching
and reduces N2O emissions. Composting manure may reduce CH4 but enhance N2O
emission from heaps. Compost use can greatly enhance carbon sequestration in the
soil compared to raw manure use. Finally, biogas production from liquid slurry makes
use of the evolving CH4 for energy and is applied by many sustainable farmers.
LOW GREENHOUSE GAS AGRICULTURE: MITIGATION AND ADAPTATION POTENTIAL OF SUSTAINABLE FARMING SYSTEMS
9
Maintaining fertile soils and restoring degraded land
IPPC Fourth Assessment Report recommended:
o
re-vegetate,
o
improve fertility by nutrient amendment,
o
apply substrates such as compost and manure,
o
halt soil erosion and carbon mineralization by soil conservation techniques such
as reduced tillage, no tillage, contour farming, strip cropping and terracing,
o
retain crop residues as covers,
o
conserve water,
o
sequester CO2 by increasing soil organic matter content.
Organic agriculture and no-till agriculture already practice these recommendations.
Techniques for improving soil fertility, applying substrates and retaining crop
residues, halting soil erosion, conserving water and sequestering CO2 are found
in both organic and conventional agriculture. In long-term experiments, carbon
sequestration rates vary considerably (see Table 2).
In the DOK field experiment in Switzerland (Mäder, et al., 2002), the stockless
conventional plots lost 207 kg carbon/ha/year during the first 28 years of the
experiment, while the bio-dynamic plots remained stable in soil organic matter
content (Fließbach, et al., 2007).
In the Rodale Farming Systems Trial in the mid-Atlantic region of the continental
USA, the manure-based organic system sequestered 1 218 kg carbon per ha and year,
the legume-based stockless organic system sequestered 857 kg, and the conventional
system sequestered 217 kg (Pimentel, et al., 2005).
Küstermann, et al. (2008) compared 18 organic and 10 conventional farms in
Bavaria, Germany and, using the REPRO model, calculated the organic farms’ annual
sequestration at 402 kg carbon, while the conventional farms had losses of 202
kg. Hepperly, et al. (2008) estimated that compost application and cover crops in
the rotation were particularly adept at increasing soil organic matter, also when
compared to no tillage techniques (see Table 4).
Agriculture can help mitigate climate change by either reducing GHG
emissions or by sequestering CO2 from the atmosphere in the soil. The application
of improved agricultural techniques (e.g. organic agriculture, conservation tillage,
agroforestry) reduces or stops soil erosion and converts carbon losses into gains.
Consequently, considerable amounts of CO2 are removed from the atmosphere.
Organic agriculture already provides effective methods to reach both of these
goals, even though there is still need for further improvement, especially with
regards reduced tillage techniques.
10
LOW GREENHOUSE GAS AGRICULTURE: MITIGATION AND ADAPTATION POTENTIAL OF SUSTAINABLE FARMING SYSTEMS
Table 4
Comparison of soil carbon gains and losses in different farming systems in long term
field experiments
FIELD TRIAL COMPONENTS
COMPARED
CARBON GAINS
(+) OR LOSSES (-)
KG C HA-1 YR-1
RELATIVE YIELDS OF
THE RESPECTIVE
CROP ROTATIONS
DOK1 Experiment,
Research Institute FiBL
and Federal Research
Institute Agroscope
(Switzerland)
(Mäder, et al., 2002,
Fliessbach, et al., 2007))
Running since 1977
Organic,
with composted
farm yard manure
+ 42 83 %
Organic, with fresh
farm yard manure - 123 84 %
Integrated Production,
with fresh farm yard
manure and
mineral fertilizer
- 84 100 %
Integrated Production,
stockless, with
mineral fertilizer
- 207 99 %
SADP, USDA-ARS,
Beltsville, Maryland (USA)
(Teasdale, et al., 2007)
Running 1994 to 2002
Organic,
reduced tillage
+ 810
to
+ 1738
83 %
Conventional, no tillage 0 100 %
Rodale FST, Rodale
Institute, Kurtztown,
Pennsylvania (USA,)
(Hepperly, et al., 2006;
Pimentel, et al., 2005)
Running since 1981
Organic, with
farm yard manure + 1218 97 %
Organic, with legume
based green manure. + 857 92 %
Conventional + 217 100 %
Frick2 Reduced Tillage
Trial, Research Institute
FiBL, (Switzerland)
(Berner, et al., 2008)
Running since 2002
Organic,
with ploughing 0 100 %
Organic,
with reduced tillage + 879 112 %
Scheyern3 Experimental
Farm, University of
Munich, Germany
(Rühling, et al. 2005),
Running since 1990
Organic + 180 57 %
Conventional - 120 100 %
1 In the DOK trial, all plots started with exactly the same soil organic matter content. In the organic
treatment where the farm yard manure was applied as compost, the SOM slightly increased whereas
in the organic and integrated systems with fresh manure, the SOM slightly decreased. The integrated
treatment with mineral fertilizers (stockless) showed a significant annual carbon loss.
2 In the Frick trial, only organic treatments are compared (ploughing versus reduced tillage). No conventional
treatment is part of the comparison.
3 In Scheyern, the experimental farm is separated into two parts, a conventional and an organic one. The
organic rotation is situated on poorer soils which explains the bigger differences in yields.
LOW GREENHOUSE GAS AGRICULTURE: MITIGATION AND ADAPTATION POTENTIAL OF SUSTAINABLE FARMING SYSTEMS
11
IS A LOW GREENHOUSE GAS EMISSION AGRICULTURE POSSIBLE?
The global GHG emissions of agriculture amount at 5.1 to 6.1 Gt CO2-equivalents (see
Figure 1, top graph). Considering that arable and permanent cropping systems of the
world have the potential to sequester an estimated 200 kg C ha-1 yr-1 and pasture systems
100 kg ha-1 yr-1, the world’s carbon sequestration may total 2.4 Gt CO2-eq. yr-1. This
minimum scenario for a conversion to organic farming would mitigate 40 percent
of the world’s agriculture GHG emissions. Lal (2004) gives similar estimates of
1.4 - 4.4 Gt CO2-eq. yr-1, considering conservation agriculture. When combining
organic farming with reduced tillage techniques, the sequestration rates on arable
land could be easily increased to 500 kg C ha-1 yr-1. This maximum organic scenario
would mitigate 4 Gt CO2-eq. yr-1 or 65 % of the agricultural GHG. These carbon
sequestration rates may be higher in depleted soils, but they may be restricted to
the time needed for reaching a new equilibrium. This indicates that the application
of sustainable management techniques that build up soil organic matter have the
potential to balance a large part of the agricultural emissions, although their effect
over time may be reduced as soils are built up. Long-term comparison field trials in
temperate climate zones have shown no slowing of sequestration for more than 30
years. Modelling of sequestration potentials of a conversion from conventional to
organic agriculture in Scandinavia gives a time span of 50 to 100 years (Foereid and
Høgh-Jensen, 2004).
By a conversion to organic farming, another approximately 20 percent of the
agricultural GHG could be reduced by abandoning industrially produced nitrogen
fertilizers (Figure 1, bottom graph), as is practiced by organic farms. This is an
encouraging figure, showing that low GHG agriculture might be possible and farming
could be climate neutral.
Eventually, a 100 percent conversion to organic agriculture could decrease global
yields. According to various studies, this yield reduction could be 30 to 40 percent in
intensively farmed regions under the best geo-climate conditions. In less favourable
regions, yield losses tend to zero. In the context of subsistence agriculture and in regions
with periodic disruptions of water supply brought on by droughts or floods, organic
agriculture is competitive to conventional agriculture and often superior with respect
to yields. Numerous case studies show that in comparison to traditional subsistence
farming, organic yields were 112 percent higher due to crop rotation, legumes and
closed circuits. Data on the competitiveness and performance of organic agriculture can
be found in Badgley, et al., 2007; Halberg, et al. 2006; Sanders, 2007; UNEP-UNCTAD
Capacity-building Task Force on Trade, Environment and Development, 2008.
Organic agriculture has huge potential, both in terms of the recommendations of the
IPCC Fourth Assessment Report and for future food security. This potential should be
considered in further climate change mitigation strategies in agricultural production.
12
LOW GREENHOUSE GAS AGRICULTURE: MITIGATION AND ADAPTATION POTENTIAL OF SUSTAINABLE FARMING SYSTEMS
o
Organic agriculture reduces erosion caused by wind and water as well as by
overgrazing at a rate of 10 million ha annually (Pimentel, 1995) – a crucial
precondition for future food security.
o
Organic agriculture is a good way to rehabilitate poor soils, restore organic
matter content and bring such soils back into productivity.
o
Organic agriculture is inherently based on lower livestock densities and can
compensate for lower yields by a more effective vegetable production. Organic
has a land use ratio of 1:7 for vegetable and animal production.
o
The potential productivity of organic farms and organically managed landscapes
can be improved considerably by scientific agro-ecological research.
o
Organic agriculture offers many added benefits such as conserving agricultural
biodiversity, reducing environmental degradation impacts and integrates
farmers into high value food chains (for a comprehensive literature study see
Niggli, et al., 2008).
LOW GREENHOUSE GAS AGRICULTURE: MITIGATION AND ADAPTATION POTENTIAL OF SUSTAINABLE FARMING SYSTEMS
13
Figure 1
Agricultural emissionons and mitigation potential
GHG emissions of the agricultural sector (Smith et al., 2007)
GHG reduction and mitigation potentials
The GHG emissions of agriculture amount at 5.1 - 6.1 Gt CO2-equivalents. With improved farm and
crop management, most of these emissions could be reduced or compensated by sequestration. A
conversion to organic agriculture would reduce industrial N-fertilizer use that emits 6.7 kg CO2-eq
per kg N on manufacture and another 1.6 percent of the applied N as soil N2O emission. It could also
enhance the sequestration of CO2 into the soils in a considerable way. For the minimum scenario, we
took a sequestration rate of 200 kg C ha-1 yr-1 for arable and permanent crops and 100 kg C ha-1 yr-1
for pastures. The maximum scenario combines organic farming with reduced tillage on arable land
(sequestration rate 500 kg C ha-1 yr-1).
Fertilisers N2O
Enteric fermentation CH4
Paddy rice CH4
Biomass burning CH4 and N2O
Manure handling CH4 and N2O
38
32
12
11
7
38%
32%
12%
11%
7%
GHG emissions of agriculture: 5.1 to 6.1 GT CO2 equivalents
6.00
5.00
4.00
3.00
2.00
1.00
0.00
Minimum Scenario Optimum Scenario
C-sequestration potential on worlds
permanent crop area
C-sequestration potential on worlds
pasture area
C-sequestration potential on worlds
arable land area
Reduction in N2O emission on farms
No production of industrial
N-fertilizers
14
LOW GREENHOUSE GAS AGRICULTURE: MITIGATION AND ADAPTATION POTENTIAL OF SUSTAINABLE FARMING SYSTEMS
THE POTENTIAL OF ECOLOGICALLY MANAGED FARMS
TO ADAPT TO CLIMATE CHANGE
As a result of climate change, agricultural production in most parts of the world not
only faces less predictable weather conditions than in previous centuries, weather
extremes will become predominant. Agriculture is not well prepared to cope with
climate change, especially in Southern Africa and Asia (Lobell, et al., 2008).
This means that our food systems must focus on building resilience as well as the
ability to adapt to a warming climate. As these attributes become more appreciated,
they also will lead to greater innovation in agriculture and food sectors.
Farmer knowledge as a key to adaptation
Intensive agriculture has neglected traditional skills and knowledge. Organic
agriculture, on the other hand, always has been based on practical farming
skills, observation, personal experience and intuition – traditional systems that
function without reliance on modern inputs. This practical adaptation “reservoir”
of knowledge (Tengö and Belfrage, 2004) is important for manipulating complex
agro-ecosystems, for breeding locally adapted seeds and livestock, and for
producing on-farm fertilizers (compost, manure, green manure) and inexpensive
nature-derived pesticides.
Improving Soil
Farming practices that conserve and improve soil fertility are important for the
future of agriculture and food production. Erratic rainfalls, droughts and floods are
expected to increase with rising temperatures. Soil organic matter can help mitigate
or avoid their negative effects while increasing primary crop productivity.
Soils under organic management retain significantly more rainwater, thanks
to the sponge-like properties of organic matter. For example, due to the sponge
properties in heavy loamy soils in a temperate climate in Switzerland, soil
structure stability was 20 to 40 percent higher in organically managed soils
than in conventional soils (Mäder, et al., 2002). In different long-term field
experiments in the USA, organic matter was considerably higher in organically
managed soil than in conventional soils, and soil stability was improved (Marriott
and Wander, 2006). In addition, higher organic matter content and more biomass
in soils make organic fields less prone to soil erosion (Reganold, et al., 1987;
Siegrist, et al., 1998)
In the Rodale Farming System Trial, the amount of water percolating through
the top 36 cm of soil was 15 to 20 percent greater in the organic systems than
LOW GREENHOUSE GAS AGRICULTURE: MITIGATION AND ADAPTATION POTENTIAL OF SUSTAINABLE FARMING SYSTEMS
15
in the conventional ones. The organic soils held 816 000 litres per ha in the top
15 cm of soil. This water reservoir was responsible for significantly higher yields
of corn and soybean in dry years (Lotter, et al., 2003; Pimentel, et al., 2005). Under
conditions in which water is limited during the growing period, yields of organic
farms are equal or significantly higher than those of conventional agriculture. A
meta-analysis of 133 scientific papers (Badgley, et al., 2007) showed that organic
agriculture was particularly competitive under the lower yield environments that
are common in developing countries. These findings underline that the technique
inherent to organic farming of investing in soil fertility by means of green manure,
leguminous intercropping, composting and recycling of livestock manure could
contribute considerably to reducing greenhouse gases while also increasing global
food productivity.
Water capture in organic plots was twice as high as in conventional plots during
torrential rains (Lotter, et al., 2003). This significantly reduced the risk of floods, an
effect that could be very important if organic agriculture were practised more widely.
Observations of biodynamic systems in India found decreased irrigation needs
of 30 to 50 percent. Better soil structure, friability, aeration and drainage, lower
bulk density, higher organic matter content, soil respiration (related to soil microbial
activity), more earthworms and a deeper topsoil layer are all associated with the
lower irrigation need (Proctor and Cole, 2002).
Experience with degraded soils in the arid tropics has shown that agricultural
productivity can be enhanced using soil fertility-building techniques. In Tigray
Province, one of the most degraded parts of Ethiopia, agricultural productivity was
doubled by soil fertility techniques such as compost application and introduction
of leguminous plants into the crop sequence. By restoring soil fertility, yields were
increased to a much greater extent at both farm and regional level than by using
purchased mineral fertilizers (Edwards, 2007).
Biodiversity and adaptation to climate change
The diversity of landscapes, farming activities, fields, and agrobiodiversity is greatly
enhanced in organic agriculture (Niggli, et al., 2008), which makes these farms
more resilient to unpredictable weather patterns that results from climate change.
(Bengtsson, et al., 2005; Hole, et al., 2005).
Organic agriculture systems build on a foundation of conserving and improving
diversity by using diverse crops, rotations and mixed farm strategies. Enhanced
biodiversity reduces pest outbreaks (Zehnder, et al., 2007; Wyss, et al., 1995;
Pfiffner, et al., 2003a,b). Similarly, diversified agro-ecosystems reduce the severity
of plant and animal diseases, while improving utilization of soil nutrients and
water (Altieri, et al., 2005).
16
LOW GREENHOUSE GAS AGRICULTURE: MITIGATION AND ADAPTATION POTENTIAL OF SUSTAINABLE FARMING SYSTEMS
CONCLUSIONS
Considering the growing concern of elevated atmospheric GHGs, the complex
economics and availability of fossil fuels, and the deterioration of the environment
and health conditions, a shift away from intense reliance on heavy chemical inputs
to an intense biologically based agriculture and food system is possible today.
Biological diversity is the keystone of ecologically based systems for the
production of food and fibre. Many components of organic agriculture can be
applied to improve all farming systems, including conventional ones.
Sustainable and organic agriculture offer multiple opportunities to reduce GHGs
and counteract global warming. For example, organic agriculture reduces energy
requirements for production systems by 25 to 50 percent compared to conventional
chemical-based agriculture. Reducing GHGs through their sequestration in soil has
even greater potential to mitigate climate change. Carbon is sequestered through
an increase of soil organic matter content. Improving soil sequestration of carbon
is desirable in both low- and high-yield crop and animal systems. However, soil
improvement is particularly important for agriculture in developing countries where
crop inputs such as chemical fertilizers and pesticides are not readily available, their
costs are prohibitive, they require special equipment, and the knowledge needed for
their proper application is not widespread.
In order to reduce trade-offs among food security, climate change and ecosystem
degradation, productive and ecologically sustainable agriculture is crucial. In that
context, organic agriculture represents a multi-targeted and multifunctional strategy.
It offers a proven alternative concept that is being implemented quite successfully by
a growing number of farms and food chains. Currently, 1.2 million farmers practise
organic agriculture on 32.2 million ha of land (Willer and Kilcher, 2009).
Many of organic agriculture’s components can be implemented within other
sustainable farming systems. The system-oriented and participative concept of
organic agriculture, combined with new sustainable technologies (such as no tillage),
offer greatly needed solutions in the face of climate change.
LOW GREENHOUSE GAS AGRICULTURE: MITIGATION AND ADAPTATION POTENTIAL OF SUSTAINABLE FARMING SYSTEMS
17
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