Laurie Drinkwater - Nitrogen

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  • How can legumes contribute to agricultural sustainability and human well-being?Laurie DrinkwaterCornell UniversityApril 2016

    Outline of my talk:

    Explain why current agricultural systems are inherently leaky and how legume-based systems differIntroduce the concept of ecological intensification as an alternative strategy for achieving sustainable food production systemsExplain the multiple, related benefits of using legumes rather than N fertilizerConnect this back to the broader benefits of using ecologically based approaches in agriculture*

  • Why are agricultural systems leaky?

    Weve heard a lot today about how N losses from agriculture impact the environment and human health. But, why are agricultural systems leaky? Is it just poor management? over application of fertilizer? *

  • Agricultural industrialization leads to declines in plant biodiversityAuclair 1976; Meyer et al. 2013

    First, we need to step back a look at how industrialization has changed the biology and ecology of agriculture. Specifically, industrialization is mainly achieved through increased reliance on fossil fuelswhich support mechanization and agrochemical inputs such as fertilizers. These inputs have enables simplification of rotations, and the dominance of monocultures. During the past several decades of industrialization, energy use increases correspond with losses of plant biodiversityboth crops and wild vegetation*

  • Fertilizer N accounts for
  • Nitrogen leakiness is a systemic problem:

    Inorganic N is highly mobile, many loss pathwaysSurplus N must be added to meet yield goalsN 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 microbesN uptake by microbes is reduced: Reduced microbial growthloss pathways predominate

    The problem with N fertilizer has much in common with other problems we face in agriculture: unexpected consequences of simplification and agrochemicals*

  • Sustainable Intensification: More crop per drop

    There are two distinct approaches being proposed to achieve agricultural sustainability*

  • Ecological intensification: Restore ecological integrity

    *

  • Ecological intensification is based on:Increase biodiversity to restore ecological processes and reduce need for chemicalsUsing 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

    So now, a few basics of nitrogen fixation to look at how this process differs from using fertilizers and to understand why it may be more efficient*

  • Our atmosphere is 78% nitrogen gas so early microbes had to find a way to access (or fix) N from the atmospherePlants and animals lack the ability to use nitrogen in this formUntil 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

    Biological nitrogen fixation is an ancient metabolic process that evolved in bacteria long before humans and higher plants were on earth. *

  • The basics of N fixationThese bacteria are everywhereIn agriculture the N-fixing bacteria associated with legumes are the most importantLegumesmore than 12,000 speciesSix legume species account for 95% of BNF in the US

    Legumes have a hugh potential to contribute to agricultural production which as barely been tapped*

  • Figure credit: Nape Mothapo, North Carolina State UniversityLegume-based cropping systems

    Heres how legumes supply N to cash crops*

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

    Three interrelated mechanismscover, C + N, reduced N surplus additions*

  • Proportion of N inputs from BNFLegume-based rotations increased SOM and soil N availabilitySchipanski and Drinkwater 2011, Nutr Cycl AgroecosysSoil N reserves

    Other benefits associated with legume N: because we are growing plants for a greater proportion of the year, and because we are adding a complete food source for the microbes/soil life*

  • Increases in SOM improve drought resistance and yield stability

    There are profound changes in soil health, which impact crops in unexpected ways.*

  • The many benefits of replacing fertilizer N with legumes contribute to sustainabilityReduced GHG emissions: Solar powered nitrogen source!Reduced need for surplus N additions reduces anthropogenic N/environmental N losses, restores SOM and soil health/tilthIncreased yield stability through improved drought resistance of cropsWhats the catch?

    *Other examples (depending on time)Greater vegetation diversity in landscapes surrounding farms increases pollinator abundance and diversity, which increases yields of crops that rely on pollinators (melons, squash, fruits)Diversified rotations suppress weeds compared to simplified rotationsIntercroppinggrowing more than one crop species in the same field as a mixture increases crop yields

  • 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 costEliminate all yield based incentive programsCarrots for farmersSticks for the agri-industrial complexExpand incentive programs for practices that reduce agro-chemical inputsTax provides of fossil fuel dependent technologies

    Many institutional, market and policy barriers existfavor the status quo*

  • Thank-you!

    *

    Outline of my talk:

    Explain why current agricultural systems are inherently leaky and how legume-based systems differIntroduce the concept of ecological intensification as an alternative strategy for achieving sustainable food production systemsExplain the multiple, related benefits of using legumes rather than N fertilizerConnect this back to the broader benefits of using ecologically based approaches in agriculture*Weve heard a lot today about how N losses from agriculture impact the environment and human health. But, why are agricultural systems leaky? Is it just poor management? over application of fertilizer? *First, we need to step back a look at how industrialization has changed the biology and ecology of agriculture. Specifically, industrialization is mainly achieved through increased reliance on fossil fuelswhich support mechanization and agrochemical inputs such as fertilizers. These inputs have enables simplification of rotations, and the dominance of monocultures. During the past several decades of industrialization, energy use increases correspond with losses of plant biodiversityboth crops and wild vegetation*Fertilizer is not really the main source of N for crops, even though we are adding extra N, it only accounts for less than 40% of the N taken up by these grain crops. The crops are still getting most of their N from the soil. Some of the extra fertilizer N goes into soil organic reserves (~20%) and the remaining fertilizer is lost to the environment.*The problem with N fertilizer has much in common with other problems we face in agriculture: unexpected consequences of simplification and agrochemicals*There are two distinct approaches being proposed to achieve agricultural sustainability*

    *So now, a few basics of nitrogen fixation to look at how this process differs from using fertilizers and to understand why it may be more efficient*Biological nitrogen fixation is an ancient metabolic process that evolved in bacteria long before humans and higher plants were on earth. *Legumes have a hugh potential to contribute to agricultural production which as barely been tapped*Heres how legumes supply N to cash crops*Three interrelated mechanismscover, C + N, reduced N surplus additions*Other benefits associated with legume N: because we are growing plants for a greater proportion of the year, and because we are adding a complete food source for the microbes/soil life*There are profound changes in soil health, which impact crops in unexpected ways.**Other examples (depending on time)Greater vegetation diversity in landscapes surrounding farms increases pollinator abundance and diversity, which increases yields of crops that rely on pollinators (melons, squash, fruits)Diversified rotations suppress weeds compared to simplified rotationsIntercroppinggrowing more than one crop species in the same field as a mixture increases crop yields

    Many institutional, market and policy barriers existfavor the status quo*

    *