How can legumes contribute to agricultural sustainability and human well-being?

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

2. Why are agricultural
systems leaky?

3. Agricultural industrialization leads to declines
in plant biodiversity
Auclair 1976; Meyer et al. 2013

4. Fertilizer N accounts for <40% of total plant N
corn spring grains winter grains
%oftotalbiomassNfromfertilizer
0
10
20
30
40
50
Gardner and Drinkwater 2009, Ecol. Applications; Based on data from 217 field-scale 15
N experiments;
40%

5. 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

6. Sustainable Intensification:
More crop per drop

7. Ecological intensification:
Restore ecological integrity

8. 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

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

10. • 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

11. 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

12. 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

13. Based on 217 field-scale 15N studies, Gardner and Drinkwater 2009, Ecol. Applications
Using legume green manures reduces N losses

14. Proportion of N inputs from BNF
Legume-based rotations increased SOM
and soil N availability
Schipanski and Drinkwater 2011, Nutr Cycl Agroecosys
SoilNreserves

15. Increases in SOM improve drought
resistance and yield stability
LEG
CNV

16. 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?

17. 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

18. Thank-you!