Agriculture and Its Effects on Natural Systems
Lecture Overview
Presented by Dakota Brooks, adapted from materials by:
Dr. Daniel J Sherman, University of Puget Sound
Dr. David R. Montgomery, University of Washington
Monterey Peninsula College Environmental Science Textbook
Lecture Outline
How Did Agriculture Develop?
Impacts of Industrialized Agriculture
How Is Meat Production Changing What We Consume?
Is Industrialized Meat Production Sustainable?
Trade-offs in Our Food Systems
9.1 How Did Agriculture Develop?
Until approximately 12,000 years ago, human groups survived through foraging, fishing, and hunting.
Foraging led to a nomadic lifestyle, limited by seasonal patterns and migratory habits.
Early cultivation practices included swiddening (slash and burn), enhancing conditions for early crop and weed plants (Sinr et al., 2015).
Early modern agriculture involved the independent development of plant cultivation and animal domestication across various ancient cultures worldwide.
Historical Agricultural Practices (1 of 2)
Humans developed breeding techniques for domesticated varieties of crops like wheat and corn through selective breeding and hybridization.
Domestication of animals progressed, starting with dogs for hunting, expanded to livestock such as cattle, chickens, and pigs for consumption.
Societies in Mesopotamia and Egypt constructed irrigation systems, including canals and dams, for crop irrigation approximately 6,000 years ago.
Fertilization using decaying organic matter began in China around 6,000 years ago.
Credit: Nicolle Rager Fuller, National Science Foundation
Historical Agricultural Practices (2 of 2)
Over 2,000 years ago, the Roman Empire initiated crop rotation and practices of resting fields (fallowing) to restore soil health.
Native Americans utilized fish to enrich soil and developed companion planting systems, notably the “3 sisters”: Beans, Corn, and Squash.
Up until the 1950s, most farms practiced mixed farming, producing various crops and livestock, allowing for manure sources, animal/human labor for cultivation, and diverse protein sources (meat, eggs, dairy).
Industrialized Agricultural Practices: Into the Modern Era
The 20th century's technological advancements led to the “Green Revolution.”
Between the 1950s and the 1990s, average grain yields tripled.
Mechanization with gas and diesel-powered tractors and harvesting equipment replaced traditional farming methods, thereby increasing productivity per person.
The synthesis of fertilizers (e.g., anhydrous ammonia) and pesticides became integral to industrial agriculture, escalating from 14 million tons in the 1950s to over 180 million tons today.
Industrialized Agricultural Practices: Irrigation and Genetic Modification
Mechanized irrigation systems boosted farmland expansion through large dams, reservoirs, aquifer pumps, and advanced sprinkler systems.
In the 1970s, genetic engineering emerged, leading to genetically modified organisms (GMOs), wherein genes from one species are spliced into another's DNA.
Some rice varieties engineered in the 1980s to produce vitamin B to combat malnutrition.
Other GMO traits allowed for tolerance to certain pesticides.
9.2 Impacts of Industrialized Agriculture
Industrialized agriculture has successfully fed billions, yet it has imposed severe environmental consequences.
Soil Health: Intensive cultivation results in exposed, bare soil prone to erosion.
Bare soil erodes 100 times faster than covered soil, eliminating soil formed over centuries.
Soil Loss and Degradation
Ineffective irrigation systems exacerbate soil erosion, particularly under excessive application rates.
Irrigation contributes to leaching—the movement of minerals beyond plant root reach.
Salinization arises from mineral salt concentration post-evaporation, which can harm plants.
Excess fertilizer can lead to lower soil pH (acidification) and a decline in organic matter, while enhancing microbial degradation.
Globally, an estimated 360,000 hectares are lost to desertification yearly due to drought, erosion, and soil infertility, resulting in over 10% productivity loss.
Water Quality and Air Pollution
Agricultural lands are significant sources of sediment entering aquatic systems, impacting light penetration and photosynthesis.
Settled sediment can smother aquatic organisms, leading to biodiversity loss and economic damage.
Only 50% of nitrogen from synthetic fertilizers benefits crops; the remainder contributes to nitrate pollution through runoff and atmospheric volatilization.
Runoff triggers eutrophication and hypoxic conditions, endangering aquatic life.
Water Availability and Shortages
Agriculture utilizes two-thirds of the world’s freshwater supply.
Groundwater supplies 40% of irrigation needs, with regions like the Ogallala Aquifer experiencing overdraft issues.
Current rates threaten the continued viability of aquifers, risking subsidence and salinity issues.
Biodiversity Loss and Pesticide Health Risks
Use of synthetic fertilizers and monocultures increased pest infestations (density-dependent factor).
Pesticide applications damage non-target populations and persist in the environment, leading to bioaccumulation in higher trophic levels.
Pesticide resistance may develop in organisms, posing health dangers to humans and resulting in approximately 20,000 pesticide poisonings among USA farmworkers annually according to the CDC.
The Loss of Agrobiodiversity (1 of 2)
The Green Revolution favored specific crop varieties, thereby reducing agricultural biodiversity and genetic diversity.
Monoculture practices lead to temporarily higher yields but increase vulnerability to pests and diseases.
The Loss of Agrobiodiversity (2 of 2)
Approximately 25,000 to 30,000 plant species are edible; historically, 1,000 to 2,500 have been domesticated.
In modern times, about 60% of human calories come from three primary crops: rice, corn, and wheat.
Corn comprises roughly 95% of livestock feed in the USA (USDA, Economic Research Service).
9.3 How Is Meat Production Changing What We Consume?
Traditionally, farms integrated livestock and crops; since the 1950s, this has shifted towards synthetic fertilizers, monocultures, and concentrated animal feeding operations (CAFOs).
Global meat consumption and seafood catches have both doubled since 1950 (FAO).
Chicken Production
The CAFO model first emerged in chicken production, breeding “broilers” optimized for meat.
Broilers receive enhanced feeds rich in proteins, amino acids, vitamins, and minerals.
CAFO conditions necessitate antibiotic use to mitigate disease and artificial lighting to promote growth, resulting in larger broilers requiring less feed and achieving reduced mortality rates pre-slaughter.
Beef Production in CAFOs
Calves are raised traditionally on grass until six months, then moved into CAFOs for fattening.
Feed consists of corn-based diets supplemented with soybeans, rendered animal fats, proteins, and occasionally synthetic growth hormones and antibiotics, leading to increased weight gains.
Cows, as ruminants, possess a four-chambered stomach for digesting cellulose through fermentation.
CAFO methods reduced the feeding period for steers from three years to 14 months.
9.4 Is Industrialized Meat Production Sustainable? (1 of 2)
CAFOs generate over 1.3 billion tons of manure yearly, exceeding human waste treatment capacities by 40 times.
Manure runoff into waterways can propagate infectious pathogens (e.g., Salmonella, E. coli) and chemical contaminants (e.g., nitrates causing blue baby syndrome).
Air pollutants arise from animal waste, bedding, and methane emissions.
Is Industrialized Meat Production Sustainable? (2 of 2)
High animal densities in CAFOs necessitate extensive antibiotic use, leading to increased antimicrobial resistance in bacterial populations, which can transfer to humans as zoonotic diseases.
Greenhouse Gas Emissions in Agricultural Production
Agricultural activity constitutes ~9% of US annual greenhouse gas emissions (GHG), with plant agriculture contributing ~5% and animal agriculture ~4% (EPA, 2024).
Major GHG sources within agriculture include mismanagement of animal waste and enteric fermentation, the latter linked to methane (CH₄) and nitrous oxide (N₂O), significantly more potent than CO₂ in heat capture (28-36 and 298 times, respectively).
Overfishing and Aquaculture (1 of 2)
Technological advancements, such as sonar and GPS, have enhanced fish capture, leading to a fivefold increase in global oceanic fish catch since 1950.
Commercial aquaculture practices involve raising seafood in controlled environments, akin to CAFOs, requiring specialized feeds and antibiotic use.
Overfishing and Aquaculture (2 of 2)
Main issues include overfishing, where catch volumes exceed species' reproductive capacities, risking population declines.
Bycatch poses another dilemma—incidental captures of non-target species lead to massive mortalities among marine wildlife.
While aquaculture mitigates overfishing and bycatch issues, it may also erode wild fish genetics and spread diseases.
9.5 Trade-offs in Our Food Systems
Agriculture is a major land-use practice, significantly impacting ecosystems—covering 40% of Earth's land surfaces.
Nearly three-quarters of all human water use is attributed to farming, with the food system accounting for one-third of total greenhouse gas emissions through direct emissions and land use alterations.
Nevertheless, agriculture plays an essential role in providing nourishment for the global population.
Life on Earth: Global Biomass Distribution
Biomass is quantified in carbon tons, with the global biomass distribution shown across taxa:
Total biomass: 546 billion tonnes of carbon.
Plants: 450 billion tonnes (82.4% of total biomass)
Bacteria: 70 billion tonnes (12.8%)
Animals: 2 billion tonnes (0.4%)
Arthropods: 1 billion tonnes (42% of animal biomass)
Fish: 0.7 billion tonnes (29% of animal biomass)
Humans: 0.06 billion tonnes (2.5% of animal biomass)
Fungi: 12 billion tonnes (2.2%)
Viruses: 0.2 billion tonnes (0.04%)
The Efficiency Argument: Eating Low on the Food Chain
Energy transfer across food chains results in ~90% energy loss.
Eating lower on the food chain minimizes energy loss, correlating with environmental benefits espoused by vegan and vegetarian diets.
Animal-based food production, especially from CAFOs, leads to increased resource use and greenhouse gas emissions.
Feed, Forage, and What's On Our Plate
Ruminant diets largely consist of plant matter that humans cannot consume, dubbed "upcycling"—transforming low-value resources into higher-value outputs.
Of the estimated 6 billion tons of dry matter used for animal feed, 86% is non-edible for humans.
Cattle require only 1.3 lb of human-edible protein to yield 2.2 lb of protein in milk and meat.
Livestock occupy approximately 4.8 billion acres, but only 1.7 billion are suitable for direct human crop production (Mottet et al., 2017).
Upcycling Between Different Species: Ruminants
Grassland ecosystems require biomass removal through grazing to maintain ecosystem health.
Ruminants can consume otherwise inedible plant species and waste products to convert them into protein-rich outputs.
Locally sourced feed reduces waste and transportation inputs.
Upcycling Between Different Species: Monogastric
Urban food waste can be processed (post-treatment) to feed hogs or poutry, exploring innovations like Black Soldier Fly larvae for livestock nutrition while preventing health risks from spoiled food.
Organic Agricultural Practices
Certified organic foods in the USA must comply with strict regulations, eschewing synthetic inputs and genetic modifications.
Farmers must employ methods like crop rotation and the use of organic nutrients.
Studies indicate that organic yields can match those from synthetic inputs, despite higher management costs.
Addressing Markets: Fair Trade and Local Production
UN estimates indicate that 75% of hunger exists within farming communities.
Transitioning to sustainable practices involves economic incentives, such as NRCS/USDA grants and Fair Trade certifications ensuring fair wages and sustainable practices.
Supporting local agriculture reduces food transport-related emissions.
Consumer-supported agriculture (CSAs) allows regular supply of food directly from local farms.
Reducing Food Waste
FAO reported that one-third of global agricultural output is wasted, primarily due to spoilage and unmarketability.
In the USA, upwards of 60% of food waste occurs at the consumer level, costing around $165 billion annually.
Wasted food represents a waste of resources and can be transformed into energy through bio-digestion.
How Can We Restore the Soil?
Sustainable agricultural practices can promote soil rehabilitation.
Methods include conservation, permaculture, biodynamic, organic, and sustainable agriculture stressing minimal disturbance, cover cropping, and rotated planting.
Enhancing soil organic matter can reduce resources needed and support carbon storage, mimicking natural ecosystems.
Suggested viewing: "Under Cover Farmers"—demonstrates adaptive management for land improvement.