laurie drinkwater - nitrogen

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How can legumes contribute to agricultural sustainability and human well-being? Laurie Drinkwater Cornell University April 2016

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Page 1: Laurie Drinkwater - Nitrogen

How can legumes contribute to agricultural sustainability and human

well-being?

Laurie DrinkwaterCornell UniversityApril 2016

Page 2: Laurie Drinkwater - Nitrogen

Why are agricultural systems leaky?

Page 3: Laurie Drinkwater - Nitrogen

Agricultural industrialization leads to declines in plant biodiversity

Auclair 1976; Meyer et al. 2013

Page 4: Laurie Drinkwater - Nitrogen

Fertilizer N accounts for <40% of total plant N

corn spring grains winter grains

% o

f tot

al b

iom

ass

N fr

om fe

rtili

zer

0

10

20

30

40

50

Gardner and Drinkwater 2009, Ecol. Applications; Based on data from 217 field-scale 15N experiments;

40%

Page 5: Laurie Drinkwater - Nitrogen

Nitrogen leakiness is a systemic problem:• Inorganic N is highly mobile, many loss

pathways

• Surplus N must be added to meet yield goals

• N uptake by plants is reduced: Simplification of rotations has led to longer and more frequent bare fallows

• Soil organic matter is reduced: less food for microbes

• N uptake by microbes is reduced: Reduced microbial growth—loss pathways predominate

Page 6: Laurie Drinkwater - Nitrogen

Sustainable Intensification: More crop per drop

Page 7: Laurie Drinkwater - Nitrogen

Ecological intensification: Restore ecological integrity

Page 8: Laurie Drinkwater - Nitrogen

Ecological intensification is based on:• Increase biodiversity to restore ecological processes

and reduce need for chemicals•Using plants that can support these processes

Plants that build fertility, suppress weeds, repel pests, attract beneficials, habitat/food for natural enemies, differing life histories

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Using legumes as a N source is one example of ecological intensification

Page 10: Laurie Drinkwater - Nitrogen

• Our atmosphere is 78% nitrogen gas so early microbes had to find a way to access (or “fix”) N from the atmosphere

• Plants and animals lack the ability to use nitrogen in this form

• Until the invention of the Haber-Bosch process life on Earth was completely dependent on the bacteria that can fix N

The basics of N fixation

Page 11: Laurie Drinkwater - Nitrogen

The basics of N fixation• These bacteria are everywhere

• In agriculture the N-fixing bacteria associated with legumes are the most important

• Legumes—more than 12,000 species—Six legume species account for 95% of BNF in the US

Page 12: Laurie Drinkwater - Nitrogen

Figure credit: Nape Mothapo, North Carolina State University

80% of N inputs are from legumes

Organic grain systems

Compost and other fertilizers Nitrogen fixation

Legume-based cropping systems

Page 13: Laurie Drinkwater - Nitrogen

Based on 217 field-scale 15N studies, Gardner and Drinkwater 2009, Ecol. Applications

Using legume green manures reduces N losses

Page 14: Laurie Drinkwater - Nitrogen

Proportion of N inputs from BNF

Legume-based rotations increased SOM and soil N availability

Schipanski and Drinkwater 2011, Nutr Cycl Agroecosys

Soil

N re

serv

es

Page 15: Laurie Drinkwater - Nitrogen

Increases in SOM improve drought resistance and yield stability

LEGCNV

Page 16: Laurie Drinkwater - Nitrogen

The many benefits of replacing fertilizer N with legumes contribute to sustainability• Reduced GHG emissions: Solar powered nitrogen source!• Reduced need for surplus N additions reduces

anthropogenic N/environmental N losses, restores SOM and soil health/tilth

• Increased yield stability through improved drought resistance of crops

•What’s the catch?

Page 17: Laurie Drinkwater - Nitrogen

What will it take to shift from industrial to ecologically-based ag systems?• Food production is too important to allow market forces to

govern how it will be grown and what it will cost• Eliminate all yield based incentive programs• Carrots for farmers—Sticks for the agri-industrial complex▫ Expand incentive programs for practices that reduce agro-

chemical inputs▫ Tax provides of fossil fuel dependent technologies

Page 18: Laurie Drinkwater - Nitrogen

Thank-you!