Environmental Benefits of Forages - Agronomic Perspective

Martin Chantigny, Ph.D.Soils and Crops Research and Development Centre, Québec

Conclusion: Cropping of perennial forages provides several environmental benefits1. Improved carbon storage in soils2. Better recycling of livestock manure3. Efficient capture of applied N (grasses)4. Reduced N needs (legumes)

Are there trade-offs, unknowns?

rootsroots Soil Soil aggregatesaggregates

timothytimothy

Perennial forages maximize the period with plant cover and active roots

A. Continuous protection against erosionB. Maximizes organic matter (C) input to soil

Why, how?Photo synth ates

(Carb on)

Angers, 1992

PerennialPerennialforageforage

CornCorn

FallowFallow

Perennial forages maximize the period with plant cover and active roots

A. Continuous protection against erosionB. Maximizes organic matter (C) input to soilC. Maximizes period for nutrient uptake

Efficient recovery of applied nutrients Split applications

Why, how?

1. Improves carbon storage in soils

To what extent? Perennial forages allocate most C to roots

(Bolinder et al. 1992; Soussana et al. 2004)

Roots contribute more to soil C than aboveground residues (Balesdent & Balabane, 1996; Bolinder et al., 1999)

C accumulation rate in Canada (vandenBygaart et al. 2008)

• 450-750 kg C/ha/yr• Compared to no-till: 60-160 C/ha/yr

RootRoot

SoilSoilaggregatesaggregates

© Martin Chantigny© Martin Chantigny

1 mm1 mmFungal hyphaeFungal hyphae(filaments)(filaments)

Relationship between fungal biomass and water-stable soil aggregation

Chantigny et al., 1997

Fungal biomass (mg C kgFungal biomass (mg C kg-1-1 dry soil) dry soil)Stab

le a

ggre

gate

siz

e (m

m)

Stab

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m)

Perennial foragesPerennial forages

Angers, 1992

CornCorn

FallowFallow

Perennial Perennial forageforage

Benefits? Increased storage of carbon in soils

Increased soil quality (fertility) Partly offsets C footprint at the farm level

Improved soil structure (aggregation) Further decreases soil erosion Further protects accumulated C

2. Better recycling of livestock manure

Maillard, 2014

After 21 yrs with dairy cattle manure (Dairy Cluster)

• Cereal monoculture: 0% of slurry-derived C retained in soil

• Cereal-forage-forage: 36% retained

2. Better recycling of livestock manure

Angers et al. 2010

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Forage with pig manure (20 yrs)

• Manure N and P also accumulate

• C/N and C/P decreases over time Increased nutrient availability? Increased « legacy » effect?

2. Better recycling of livestock manure

Nyiraneza et al., 2010

After 28 yrs with dairy cattle manure• Legacy effect in continuous corn

47 kg N/ha to corn the next year

• Legacy effect in corn-forage-forage 208 kg N/ha to corn after forage

Benefits? Synergistic effects

• Improved retention of manure C Further reducing C footprint at farm level

• Favors retention of manure N and P Augmented legacy effect of manures

Benefits? Reduces the risk of N loss to environment

Lower GHG emissions (N2O):

• Perennial grasses: 0.05 to 1.5% (Chantigny et al. 2007; Rochette et al. 2014)

• Annual crops: 1-4% (Chantigny et al. 2010; Pelster et al. 2012)

3. Efficient capture of applied N (grasses)

Chantigny et al. 2013

Cropping system N2O-N emission factor(% of applied N)

  2011 2012 Mean

Continuous barley

Forage 1st yr

Forage 2nd yr

2.99

0.11

0.62

1.14

0.23

0.70

2.07

0.17

0.66

Proportions of manure N lost as N2O after 21-22 yrs with dairy manure (Dairy cluster I)

Benefits? Reduces the risk of N loss to environment

Lower N (NO3) leaching index (Cardenas et al. 2013):

• Perennial grasses: up to 9% of applied N

• Annual crops: up to 28%

3. Efficient capture of applied N (grasses)

4. Reduced N needs (legumes)

To what extent? Legumes can fix 100 to 380 kg N/ha/y

(Lüscher et al. 2014)

In mixture with grasses:• Increased net primary productivity• Stimulates soil C and N storage

(Soussana et al. 2004; Lüsher et al. 2014)

Benefits?

Reduced need for N fertilizers Decreased C footprint of farm Increased farm profitability

Process self-regulated by soil sink intensity (Lüscher et al. 2014) Reduced risk of N loss as compared to

commercial fertilizers

Are there trade-offs?Perennial forages favour accumulation of C, N, P in soils Increases risk of environmental loss upon

cultivation/renovation (MacDonald et al. 2010; 2011; 2012)

Can we avoid it? Rapid re-establishment of forage stand Planting catch crop in the fall Planting nutrient-demanding crop next year

Are there trade-offs?

Toor et al. 2005; Aronsson et al. 2014

Soil undisturbed P accumulates at the soil surface: P run-off Biopores, cracks: P leaching (preferential flow)

• Especially problematic in manured soils with tile drains

Can we avoid it? Increase residence time of manure in the soil

profile• Split applications (lower rates)

Are there trade-offs?Soil undisturbedAmmonia volatilization (liquid manures)

• Must be incorporated to limit volatilization• Soil tillage is not possible

Can we avoid it?Increase infiltration rate of liquid manures

• “Separation” of solids to decrease slurry viscosity• Open slots

Van Vliet et al. 2006; Bittman et al. 2011

Manure spreader mounted on a soil aerator with trail hoses installed behind aerator tines (e.g. van Vliet et al. 2006)

Unknowns?

Fate of nutrients during winter? In arable soils: GHG emissions and leaching

occur throughout winter • 20-90% of annual losses (Chantigny et al. 2013)

Perennial forages: winter survival• Plant death = decomposition of organic matter• Are overwinter losses comparable, smaller, greater?• Could be significant in grasslands

(Virkajärvi et al. 2010; Fuller et al. 2012)

Unknowns?

Legacy effect (crop rotation)How to account for in fertilizer recommendations?

• As a function of manure history

• As a function of stand composition (% legumes)

QUESTIONS ?