Agroecology Exam 1 But Good Good

Evolution (Darwin's definition)

Descent with modification: heritable traits in populations change over generations through natural selection

Recipe of evolution

1) Variation in a population 2) Variation is heritable 3) Differential survival/reproduction (selection) -> allele frequencies change over time

Agriculture

Human management of plants/animals (a managed ecosystem) to produce food, fiber, and fuel

Ecology

Study of interactions between organisms and their environment

Evolution vs. ecology

Evolution = change in heritable traits of populations across generations (long timescale); ecology = interactions among organisms and environment (current timescale). Ecology provides the selection pressures that drive evolution

Proximate causation

The immediate mechanism or "how" something happens

Ultimate causation

The underlying evolutionary/historical reason or "why" something happens

How evolution contributes to agricultural sustainability

Pests, weeds, and pathogens evolve resistance; genetic diversity gives crops adaptive potential; management that works with evolutionary principles (rotation, diversity) slows resistance

Thomas Malthus

Economist who argued population grows geometrically while food grows arithmetically, so famine/disease/war are inevitable checks on population

Flaws in Malthus's theory

Underestimated technological change (fertilizer, breeding, Green Revolution); ignored the demographic transition (birth rates fall with development); hunger is often a distribution/access problem, not total supply

Tragedy of the commons

Hardin (1968, Science): individuals sharing a resource each gain by adding "one more animal" while costs are shared, so rational self-interest leads to overuse and ruin of the resource

Hardin's two proposed solutions

1) Private property (privatization) 2) Government regulation / "mutual coercion, mutually agreed upon"

Flaw in Hardin's parable (per Bollier)

He described an open-access free-for-all (no boundaries, rules, community, or sanctions), not a true commons

What a real commons has

Boundaries, rules, social norms, sanctions against free riders, and a community of stewards

William Forster Lloyd

English lecturer (1832) whose pooled-money/shared-pasture argument inspired Hardin; same flaw of assuming users can't communicate

Elinor Ostrom

Political scientist; first woman to win the Nobel in Economics (2009); showed through fieldwork that communities can self-govern common-pool resources sustainably; wrote Governing the Commons (1990)

Common-pool resource (CPR)

Collective resource (fisheries, grazing land, groundwater) where exclusion is difficult and use by one reduces availability for others

Ostrom's design principles (part 1)

1) Clearly defined boundaries (who can use) 2) Rules fit local conditions, with limits on what/how much can be taken 3) Users can create or influence the rules (collective choice)

Ostrom's design principles (part 2)

4) Users monitor the resource 5) Graduated sanctions for rule-breakers 6) Easy access to conflict-resolution mechanisms

Ostrom's design principles (part 3)

7) Outside authorities recognize the community's right to organize 8) Nested enterprises / polycentric governance (local to regional to national to international)

Examples of successful commons (Ostrom)

Törbel, Switzerland (alpine meadows/forests/irrigation since 1224); Spanish huerta irrigation; LA groundwater authorities; Maine lobstermen

Tragedy of the market (Bollier)

Heedless pursuit of private gain without regard for collective or systemic harm (e.g., the 2008 financial crisis) describes the market better than a commons

Aldo Leopold's solution

The Land Ethic: an ethical (not just economic) relationship to land

Land Ethic

Extends the ethical community to include soils, waters, plants, and animals ("the land"); humans are plain members and citizens of the community, not conquerors

How the Land Ethic counters Hardin

Hardin offers economic self-interest (privatization) or coercion; Leopold says responsibility comes from ethics and belonging to a community, not ownership or force

"Think like a mountain"

Leopold's essay on killing a wolf: removing predators led to deer overpopulation, overgrazing, and erosion. Take the long-term, whole-ecosystem view; everything is interconnected

Commodity

A standardized, interchangeable good (corn, wheat, soy) whose price is set by the market, so producers can't differentiate their product

How commodity agriculture homogenizes farming

Low, volatile prices push farmers to maximize volume and cut costs, so they specialize, grow monocultures, use the same high-yield varieties, and expand

Industrial agriculture and US farm numbers/size

Farm numbers fell sharply (about 6.8 million in the 1930s to about 2 million today) while average farm size rose; mechanization, cost-price squeeze, "get big or get out"

Context (economics) and global farm size distribution

Low-income countries have many small farms (labor abundant, land/capital scarce); high-income countries have fewer, larger farms (capital/mechanization, land consolidation); policy and land tenure also matter

Domestication

Genetic change in a species through human selection so that it suits human needs

Purpose/benefits of domesticating crops

Higher yield, larger edible parts, uniform germination and harvest, non-shattering seeds, reduced toxins/bitterness, predictability

Domestication as a zero-sum game

Energy put into traits humans want (yield, palatability) comes at the expense of traits plants need to survive (defenses, adaptability), so crops depend on human management

Effect of domestication on plant defenses

Reduced chemical and physical defenses, so crops are more vulnerable to pests, disease, and competition

Effect of domestication on management

Crops need more inputs and care (weeding, pest control, fertilizer, irrigation, replanting)

Why save seeds?

Local adaptation, independence and lower cost, preserve genetic diversity as insurance against disease/climate, cultural heritage, material for breeding

Change in seed diversity over 100 years

Dramatic loss; roughly 75% of crop genetic diversity is commonly cited as lost in the 20th century. Two-thirds of US corn acreage is planted with just four varieties (Seeds of Resistance)

Nikolay Vavilov

Russian botanist; led 100+ expeditions to 64 countries collecting seeds; built the largest seed collection (St. Petersburg); identified centers of origin; died in Stalin's prison

Vavilov's life's work

Collecting and cataloguing crop diversity and wild relatives to strengthen crops; identifying "centers of origin" (Vavilov Centers); showing that diverse local varieties reduce disease/pest damage

Vavilov Centers

Species-rich regions near the equator where most crops originated; wild relatives there hold valuable resistance genes

Luther Burbank

American breeder in Sonoma County, CA; brought seeds to him by mail; developed Santa Rosa plum, pluot, Burbank russet potato; advocated plant patents (Plant Patent Act 1930)

Plant Patent Act (1930)

Allowed patents on asexually reproduced plants; later expansions to sexually reproducing plants (about 50 years later) opened the door to the modern seed industry

1970 Southern corn leaf blight

Fungus (Helminthosporium maydis) hit corn with Texas male-sterile cytoplasm (T cytoplasm), planted on over two-thirds of US corn acres; US yields fell about 15%

Why the 1970 blight spread so fast

Genetic uniformity: nearly all plants had the same DNA and the same susceptibility

How the corn blight was fixed

Breeders crossed in resistance from Mexican landraces and teosinte, the wild ancestor; Oaxaca/Mexico is corn's center of origin

Irish potato famine

1845 blight (Phytophthora) devastated Ireland's nearly genetically identical potatoes (from one introduced strain); at least half a million deaths and mass emigration

National Academy of Sciences 1972 report

Found US crops "impressively uniform genetically"; blamed economic and legislative forces (subsidies, insurance, tax incentives); recommended broadening gene pools, spreading seed varieties, and preserving native/wild varieties

Other uniformity-linked crop disasters

Goss's wilt (B-14 hybrid corn), grey leaf spot (1990s), bananas, Hawaiian papayas, Jordanian tomatoes, Syrian wheat/cotton monocultures before the 2010 drought

International Treaty on Plant Genetic Resources

Countries share public germplasm in exchange for payments to a fund supporting biodiversity in origin countries; the US ratified in 2016; funding remains disputed

Dust Bowl proximate causes

Severe 1930s drought, high winds, bare tilled soil, loss of native prairie grass, and wheat monoculture with deep plowing

Dust Bowl ultimate causes

Economics and policy: high WWI wheat prices, homesteading, mechanization (tractors), expansion onto marginal land, commodity price pressure, no conservation practices

Government interventions after the Dust Bowl

Agricultural Adjustment Act 1933 (price supports, paid acreage reduction); Soil Conservation Service 1935; Shelterbelt Project; Taylor Grazing Act 1934; Commodity Credit Corporation loans; Federal Crop Insurance 1938

How commodity pricing drives conventional production

Farmers are price-takers, so they cut costs, increase scale and yield, specialize, and depend on inputs and government supports

Why "Green" Revolution?

Term coined by USAID's William Gaud (1968) as a contrast to a "red" (communist) revolution; also refers to green high-yield crops

Norman Borlaug

Agronomist; developed semi-dwarf, disease-resistant (rust), high-yield wheat; shuttle breeding; Nobel Peace Prize 1970

Borlaug's major breakthroughs

Semi-dwarf wheat that doesn't lodge under heavy fertilizer; rust resistance; shuttle breeding (two growing seasons per year) and photoperiod insensitivity so varieties adapt widely

Hybrid plants

Offspring of crossing two genetically distinct inbred parent lines

Hybrid vigor (heterosis)

F1 hybrids outperform both parents in yield and vigor

Drawbacks of hybrids

Farmers must buy seed every year (saved seed loses vigor), genetic uniformity and vulnerability, need for inputs, loss of diversity, seed industry control

Green Revolution definition (John & Babu)

Increased crop productivity via more area farmed, double-cropping, HYV seeds, fertilizers and pesticides, irrigation, and mechanization; led by M.S. Swaminathan in India

Green Revolution benefits

Cereal production tripled with only about 30% more land; less hunger and poverty; lower food prices; India went from ship-to-mouth imports to self-sufficiency; spared land from conversion

Green Revolution criticisms

Pesticide overuse, residues, and pest imbalance; groundwater depletion (Punjab, rice/wheat); soil and water pollution; reliance on inputs; farmer debt; poor health outcomes; loss of diversity; ignored ecological principles

Geopolitics of the Green Revolution

Cold War strategy to reduce hunger-driven unrest and communism; Rockefeller and Ford Foundations and US government exported HYV technology to Mexico, India, the Philippines

MAP (Mexican Agricultural Program)

1943 Rockefeller Foundation program with the Mexican government to improve wheat and corn; birthplace of Green Revolution breeding

Why Rockefeller chose Mexico

Close to the US, food shortages and political stability concerns, diverse environments and center of maize origin, government willingness (spurred by VP Henry Wallace)

J.G. Harrar (1955)

Rockefeller Foundation agriculture director; argued food security needs education, social responsibility, and science together; techno-optimist (genetics, hybrid vigor, chemicals); noted 10-15% of US food wasted

Haber-Bosch process

Converts atmospheric N2 + H2 into ammonia (NH3) at high temperature and pressure with an iron catalyst; uses fossil fuel (natural gas)

Why Haber-Bosch mattered for the Green Revolution

Cheap synthetic nitrogen fertilizer let the new dwarf, fertilizer-responsive varieties reach their high yield potential

Green Revolution and genetic diversity

Replaced diverse landraces with a few uniform HYVs, causing homogenization and genetic erosion

Soil texture

Proportions of sand, silt, and clay. Sand drains fast but holds few nutrients; clay holds water and nutrients (high CEC) but drains poorly; loam is the balance

Characteristics of healthy soil

Good structure/aggregation, high organic matter, active biology, good infiltration and water holding, nutrient cycling, balanced pH, low erosion and compaction

Organic matter: three levels

1) Living organisms (roots, microbes, fauna) 2) Fresh/dead residues (active fraction) 3) Humus (stable, well-decomposed)

Soil organic matter vs. soil organic carbon

SOM is about 58% carbon, so SOM = SOC x 1.72 (roughly)

Benefits of living organic matter

Nutrient cycling, decomposition, aggregate formation, disease suppression

Benefits of fresh residues

Food for microbes, quick nutrient release, surface cover against erosion

Benefits of humus

High CEC and water holding, long-term nutrient storage, stable structure, dark color/warmth

How to maintain or increase soil OM

Cover crops, compost/manure, crop rotation, residue retention, reduced tillage, perennials, avoid bare soil

How OM is lost

Tillage (oxidation), erosion, bare soil, residue removal, leaching, high temperature and moisture speeding decomposition

Factors determining potential soil OM

Climate (temperature, moisture), texture (clay), vegetation type, topography, drainage, time, management

Bulk density

Dry soil mass per unit volume (g/cm3)

Measuring bulk density

Take a core of known volume, oven-dry it, weigh, and divide dry mass by core volume

Why bulk density matters

Indicates compaction; high values restrict root growth, water infiltration, and aeration

Tillage and organic matter

Tillage aerates soil, increasing oxygen, which boosts microbial activity that "burns up" organic matter; it also breaks aggregates and exposes soil to erosion

Cation exchange capacity (CEC)

Soil's ability to hold positively charged ions (Ca2+, Mg2+, K+, NH4+) on negatively charged clay and humus

CEC and nutrient retention

High-CEC soils retain cations and resist leaching; anions like nitrate (NO3-) aren't held and leach easily

Major determinants of nutrient solubility/bioavailability

pH, soil minerals, organic matter, moisture/redox conditions, and the chemical form of the nutrient

pH

Measure of H+ concentration (-log[H+]); scale 0-14; 7 is neutral

Why pH affects solubility

Low pH increases Al/Mn toxicity and binds P to Al/Fe; high pH binds P to Ca and reduces micronutrient availability; most nutrients are best around pH 6-7

Nitrogen cycle

N2 -> fixation -> NH4+ -> nitrification -> NO3- -> plant uptake; organic N

Major ways N2 becomes available

Biological fixation, Haber-Bosch fertilizer, lightning

Nitrogen fixation

Conversion of N2 to ammonia (via nitrogenase); best known in legumes with Rhizobium, plus free-living bacteria (Azotobacter) and cyanobacteria

Denitrification

Anaerobic bacteria convert nitrate (NO3-) to N gases (N2, N2O), causing N loss

Conditions leading to denitrification

Waterlogged/anaerobic soil, available carbon, warm temperature, nitrate present; bacteria use NO3- in place of oxygen

Mineralization

Microbes convert organic N to plant-available ammonium (NH4+)

Immobilization

Microbes take up inorganic N, temporarily tying it up (especially with high-carbon residues)

Why drainage matters for fertility

Good drainage keeps soil aerobic and prevents denitrification, but excessive drainage leaches nitrate

Nitrogen-fixing bacteria

Rhizobia live in legume root nodules, convert N2 to NH3, and receive plant sugars; N reaches soil through residue/nodule decomposition and root exudates

Phosphorus cycle

Sedimentary cycle from rock weathering to soil solution to plants to organic P to soil binding; no significant gaseous phase

Phosphorus vs. nitrogen cycle

N has an atmospheric reservoir and gaseous losses; P comes from rock, has no gas phase, and is far less mobile

P mobility compared to N

P is immobile (binds tightly to soil particles, moves mainly with erosion); nitrate is highly mobile and leaches