Legumes - INTA

Legumes –
moderating climate change and
future potentials
Anna Mårtensson
Lucrecia Noemí Brutti
Swedish University of Agricultural Sciences
www.slu.se

Los balances de carbono y
nitrógeno de los suelos pampeanos
ante el creciente proceso de
agriculturización
C and N in Pampean soils
• PICT/PRH (Nº 267)
• Los balances de carbono y nitrógeno de )
los suelos pampeanos ante el creciente
proceso de agriculturización
• Lucrecia Noemí Brutti
• INTA, Instituto de Suelos
• Experimental INTA Oliveros
• Anna Mårtensson
• SLU Departamento de Ciencias del Suelo
Swedish University of Agricultural Sciences
www.slu.se

Challenges for agriculture!
• Food for a rapidly expanding population
• Lower the risk of climate change by reducing net
release of anthropogenic green house gases
• Increased demand for energy in face of peak oil
Swedish University of Agricultural Sciences
www.slu.se

Can legumes
• Lower the emissions of green house gases compared to
N-fertilized systems?
• Reduce fossil energy used in production of food and
forage?
• Contribute to the sequestration of C in soils?
• Provide a viable source of biomass for biofuels and other
materials?
Swedish University of Agricultural Sciences
www.slu.se

The potential to moderate climate
change
• Climate change is brought about by increasing
atmospheric content of a range of greenhouse gases
(GHG) such as CO2, N2O and CH4
• GHG are all increasing as a result of human activity
Swedish University of Agricultural Sciences
www.slu.se

Rising CO2 levels are the main
concern
• CO2 emissions from the combustion of fossil fuels
account for >50% of the estimated greenhouse effect
Swedish University of Agricultural Sciences
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Agricultural contribution of GHG emissions
= 13.5% of the total GHG CO2 equivalents
Derived mainly from:
• Use of fossil energy for the manufacture and transport
of fertilizer N, other fertilizers and agrochemicals
• Changes in land-use that release GHG when stored C
in wood is converted to CO2 by burning when land is
deforested for cropping or livestock
Swedish University of Agricultural Sciences
www.slu.se

• the release of N2O from soils as a result of
inefficiencies in crop recovery of fertilizer
and other soruces of N
• CH4 released from enteric digestion of
forage within the rumen of livestock, onfarm
management and rice cultivation on
wetlands
Swedish University of Agricultural Sciences
www.slu.se

The potential to moderate
climate change
• 1-2% of total world energy consumption is used for synthesis
of N fertilizer
• Annual global fertilizer production is 100 Gt (1 Gt= 10 9 g)
Swedish University of Agricultural Sciences
www.slu.se

N-fertilization and CO2
• 1 kg NH3-N produced generates 0.7-1.0 kg CO2-C which
gives 300 Gt of CO2 released in atmosphere each year
• About half of that CO2 will be reused if NH3 is converted to
urea (67% of the total N fertilizer) – but will rapidly
hydrolyze in soil and the captured CO2 will be released
Swedish University of Agricultural Sciences
www.slu.se

• 33 - 46 Gt N is annually fixed by legumes
• 10 g more CO2 are respired for every gram N
assimilated cf. to if the plant has used fertilizer or soil N
instead
• 350-500 Gt of additional CO2 is therefore respired from
legume roots each year as a result of fixation
• 300 Gt CO2 is emitted annually from the manufacture of
100 Gt fertilizer N
Swedish University of Agricultural Sciences
www.slu.se

N-fertilization and CO2 emissions
CO2 release related to legume fixation balance
CO2 release related to N fertilizer
Main difference!
CO2 respired from the legumes originates from
photosynthesis and will not represent a net
contribution to atmosphere
Swedish University of Agricultural Sciences
www.slu.se

N2O emissions
5% of the green house effect attributed to
N2O of which 60-70% is calculated to derive
from animal and crop production
Swedish University of Agricultural Sciences
www.slu.se

N2O emissions
Total N2O fluxes from legumes and N-fertilized systems
vary enormously!
Swedish University of Agricultural Sciences
www.slu.se

Examples of total N2O emissions from field-grown legumes
Category/species
Alfalfa 1.99
White clover 0.79
Lupin 0.05
Field pea 0.65
Soybean 1.58
Mean of all legumes 1.29
N-fertilized pasture 4.49
N-fertilized wheat 2.73
N-fertilized maize 2.72
Mean fertilized 3.22
systems
Soil no fertilizer, no 1.20
legume
(data adopted from Jensen et al 2011)
Total N 2 O emission per growing
season or year in kg N 2 O-N ha -1
Swedish University of Agricultural Sciences
www.slu.se

Examples of total N2O emissions from crop rotations with
annual legumes
Crop
Soybean-wheat
(0 N soybean, 45
kg N wheat) Brazil
Soybean-vetch
(0 N) Brazil
Maize-wheat
(0 N maize, 45 kg
N wheat) Brazil
Soybean
(44 kg N) USA
Maize
(215 kg N) USA
Total N 2 O emission per growing
season in kg N 2 O-N ha -1
0.81
0.73
0.83
7.1
12.7
(data adopted from Jensen et al 2011)
Swedish University of Agricultural Sciences
www.slu.se

The potential to moderate climate
change - Conclusions
• CO2 emissions balance N fertilizer emissions but will not
represent a net contribution to atmosphere
• Losses of N2O from legume soil generally lower than
from N-fertilized systems especially at high rates of N
fertilization or badly timing
Swedish University of Agricultural Sciences
www.slu.se

Precautions - N2O losses may occur
• following termination of legume-based pastures
• when using legumes as green-manure and there is a
rapid build-up of high levels of nitrate in soil
Swedish University of Agricultural Sciences
www.slu.se

Reasons for this is that:
• Legume tissues are high in N and low in C/N ratios
compared to non-legumes
• Legume residues are more likely to result in net
mineralization and a build-up of nitrate in soil which may
result in N2O emissions caused by denitrifying microbes
Swedish University of Agricultural Sciences
www.slu.se

NB!
N losses from legume residues is determined by how well the
release (supply) of mineralized N is synchronized with the
demand of N by the following crops
Good farming practise make a change here!
Swedish University of Agricultural Sciences
www.slu.se

Energy use by legume-based and N-
fertilized systems
• Fossil fuel is used in both systems for:
– production of seed for sowing
– by on-farm machinery for tillage, sowing, harvesting
– in manufacture, transport and application of
fertilizers
– other agrochemical inputs used to either supplement
crop nutritional requirements or for crop protection
Swedish University of Agricultural Sciences
www.slu.se

Comparisons of energy use by legume-based
and N-fertilized systems
Fossil fuel is used in both legume and non-legumes cropping
systems but…
• 35% to 60% less fossil energy is used by legumes cf. to N-
fertilized cereals/grass-lands
• 12-34% less energy is used by including legumes in the
rotation
Swedish University of Agricultural Sciences
www.slu.se

Fossil energy consumed by field pea or barley
Parameter Pea Barley
Diesel (MJ/ha) 3320 3400
N fertilizer (kg 0 130
N/ha)
N fertilizer
(MJ/ha)
Seeds and non-
N fertilizers
(MJ/ha)
Pesticides
(MJ/ha)
Total fossil
energy used
(MJ/ha)
Harvested
product (kg
DM/ha)
Energy input
(MJ /kgDM)
0 6500
2770 1860
900 900
6990 12660
6000 8000
1.16 1.58
(adopted from Peoples
et al 2009)
Swedish University of Agricultural Sciences
www.slu.se

Location
Annual energy use
(MJ/ha) in the rotation
With legumes
No legumes
Germany 21 100 24 500
France 19900 22500
USA 4305 5699
Canada 7773 9714
Swedish University of Agricultural Sciences
www.slu.se

Rationale for less energy use in
legume-based cropping systems
• Reduced energy - no need to apply N fertilizer
• Lower N fertilizer requirements for following crops
• Lower use of agrochemcials for crop protection
Swedish University of Agricultural Sciences
www.slu.se

Conclusions - energy use by legume-based and
N-fertilized systems
Fossil fuel is used in both legume and non-legumes cropping
systems but…
• 35% to 60% less fossil energy is used by legumes cf. to N-
fertilized cereals/grass-lands
• 12-34% less energy is used by including legumes in the
rotation
Swedish University of Agricultural Sciences
www.slu.se

Role of legumes-soil carbon sequestration and
land use change
Soils contain large amounts of C in both inorganic and
organic forms
Inorganic forms are derived from geological or soil
parent material sources (carbonate, bicarbonate)
Swedish University of Agricultural Sciences
www.slu.se

Soil organic matter
• Organic C (SOC) in soil ranges between 200 t C/ha
in top 30 cm (if 25 t/ha that equals 400 sheep)
• Different pools (roots, fresh residues, living microbes,
macrofauna represent

Role of legumes-soil carbon
sequestration and land use change
• Atmosphere contains 750 Gt (1Gt=10 9 g) of C as CO2
• Globally top meter of soils stores approx 1500 Gt in SOC
and 900-1700 Gt as inorganic C and exchanges 60 Gt each
year with the atmosphere
Swedish University of Agricultural Sciences
www.slu.se

Role of legumes-soil carbon
sequestration and land use change
• The amount of C accumulated in a soil is dependent
upon the balance between C inputs and losses
• In practice new C can only be introduced to soil via
photosynthesis by plants
• Any farm management practice that enhances total
plant production contribute to increasing soil C content
Swedish University of Agricultural Sciences
www.slu.se

C losses from the soil system
• Leaching of dissolved and particulate C
• Wind and water erosison
• Microbial decomposition and mineralization that convert C
in fresh plant residues and SOC into CO2
Swedish University of Agricultural Sciences
www.slu.se

Potential for soil C sequestration
Greatest potential in perennial systems
• SOC doubled by introducing Desmodium ovalifolium
into a Barchiaria sward over a 9-year period from
0.66 to 1.17 t C/ha (Brazil)
• SOC increased by 70% in grass/clover cf. to monograss
given 350 kg N/ha year which increased SOC
by 40% (19 years study)
Swedish University of Agricultural Sciences
www.slu.se

Two scenarios:
• Legume roots are N-rich which stimulates biological
activity resulting in a decrease of the metabolizable C
fraction of the SOC -> SOC decreases
• C sequestration of stable carbon in humus may be N-
limited. N-rich root residues will when contribute to the
long-term C storage in humus ->SOC increases
Both can be true simultaneously. I dare not express an
opinion on the net.
Swedish University of Agricultural Sciences
www.slu.se

Generally, and to my experience, annual crops
normally lowers SOC, as soils are much cultivated
and soil microbes become stimulated resulting in
need for C for their metabolic processes
A question is whether annual legumes lower SOC
more than other legume crops
Swedish University of Agricultural Sciences
www.slu.se

Replacing fossil fuels?
• Global energy demand expected to increase by 45% by 2030
• Fossil fuels account for 80% of the world energy required
• Biomass can potentially replace fossil hydrocarbons for heat,
power, soild and liquid fuels, materials and chemcials
Swedish University of Agricultural Sciences
www.slu.se

Replacing fossil fuels?
• World demand for renewable biomass for energy
production is predicted to increase
• The consequences of reallocating land from food
production to bioenergy purposes remains controversial
Swedish University of Agricultural Sciences
www.slu.se

Biomass production for bioenergy
• requires a high net biomass per unit area
• a low amount of fossil energy input
• results in a low fossil energy requirement per kg DM
produced
Swedish University of Agricultural Sciences
www.slu.se

Replacing fossil fuels?
Currently: High fertilizer inputs to support the growth of
high yielding biomass crops
Future: The attraction of legumes is their ablity to satisfy
their own N requirements
Swedish University of Agricultural Sciences
www.slu.se

Replacing fossil fuels?
• Although legume yields has increased, enhancements are
small compared to wheat and maize
• 700 million ha of cereals 2009
• 193 million ha of pulses/legume oilseed crops 2009
Swedish University of Agricultural Sciences
www.slu.se

Replacing fossil fuels?
Legumes are lower yielding and have higher protein
concentrations than cereals which have resulted in less
interest for use as biofuels
Swedish University of Agricultural Sciences
www.slu.se

Data adopted from Jensen et al 2011
Swedish University of Agricultural Sciences
www.slu.se

Legumes for production of heat,
syngas, biooil and char
• Pyrolysis of biomass involves combustion of the
biomass without oxygen and result in syngas,
biooil and biochar
• Pyrolyzing straw from high biomass soybeans
resulted in 70% biooil, 20% biochar and 10%
syngas
Swedish University of Agricultural Sciences
www.slu.se

Legume for diesel-
Second-generation conversion
technology for lignocellulose
• Promising, vegetative biomass from oilseed legumes
is a possible source
• Perennial legumes option - efficient use of resources
and lower farming operations
Swedish University of Agricultural Sciences
www.slu.se

Energy balance for soybean diesel production
assuming 2824 kg grain/ha with 18% oil resulting in
480 L biodiesel
• 18 GJ used for operation (field prep., seeds, fertlizer,
pesticides, amchinery, farm labor)
• 58 GJ total bioenergy yield
• 4 GJ used for transesterification (biodiesel)
• Total energy balance 2.6:1
Swedish University of Agricultural Sciences
www.slu.se

Legumes as feedstocks for biogas
plants
Anaerobic digestion is a key technology for the sustainable
use of organic biomasses from industrial and urban organic
wastes, animal manures, crop residues and energy crops
• Farm size to big industrial plants
• Digest residues rich in nutrients (N)
Swedish University of Agricultural Sciences
www.slu.se

Methane potential of some legumes
Methane potential
(m 3 /kg volatile solids)
Maize 0.38
Alfalfa 0.34
Lupin 0.33
Red clover 0.29
Grass 0.34
Swedish University of Agricultural Sciences
www.slu.se

Conclusion
Need for new breeding programs to increase dry matter
yields in legumes if those should be competetive for
energy use
Swedish University of Agricultural Sciences
www.slu.se

Other uses, legumes
Constituents:
sugars
amino acids
phytochemicals
lignin
tannins
Potential use as:
surfactants
biopolymers
glues
industrial chemicals
biopesticides
nutriceuticals
pharmaceuticals
Swedish University of Agricultural Sciences
www.slu.se

Legumes as pharmaceuticals
• seed proteins control metabolic disorders
(cholesterol-lowering effect of soybean 7S
globulin subunite)
• immobilization of insulin by lupin conglutin
to control glycemia
Swedish University of Agricultural Sciences
www.slu.se

Legumes are rich in isoflavones
• Isoflavones are
estrogenic
anti-angiogenic
antioxidative
anti-cancer acting
• They also prevent
osteooporosis
cardiovascular diseases
Swedish University of Agricultural Sciences
www.slu.se

Legumes contain condensed tannins
and polyphenols
• Antioxidative
• Potentially health promoting (cardiac
health and immune defense)
• Faba beans compound inhibit human
cancer cells
Swedish University of Agricultural Sciences
www.slu.se

Saponins in legumes
• Detere herbivore grazing
• But are also allelopathic
• Antimicrobial
• Anti-insect
• Foam-producing/detergent
Swedish University of Agricultural Sciences
www.slu.se

Legumes for use in future biorefineries
Swedish University of Agricultural Sciences
www.slu.se

Take home message!
Legumes are unique plants!
• They reduce emissions of fossil energy-derived CO2 and
lower N2O fluxes by fixing N
• They reduce the use of fossil energy
• They enhance soil C sequestration
• They provide a valuable source for bioenergy materials
and chemicals and will be important components in coming
biobased economies
Legumes are important in future agro-ecosystems!!!
Swedish University of Agricultural Sciences
www.slu.se