Download - Laurie Drinkwater - Nitrogen
How can legumes contribute to agricultural sustainability and human
well-being?
Laurie DrinkwaterCornell UniversityApril 2016
Why are agricultural systems leaky?
Agricultural industrialization leads to declines in plant biodiversity
Auclair 1976; Meyer et al. 2013
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
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zer
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10
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Gardner and Drinkwater 2009, Ecol. Applications; Based on data from 217 field-scale 15N experiments;
40%
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
Sustainable Intensification: More crop per drop
Ecological intensification: Restore ecological integrity
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
Using legumes as a N source is one example of ecological intensification
• 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
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
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
Based on 217 field-scale 15N studies, Gardner and Drinkwater 2009, Ecol. Applications
Using legume green manures reduces N losses
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
Increases in SOM improve drought resistance and yield stability
LEGCNV
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?
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
Thank-you!