Unit 5

Big Idea & Enduring Understanding

  • When humans use natural resources, they alter natural systems.

  • Agricultural practices have shifted dramatically due to population growth, technology, and global food demand.

5.3 β€” Agricultural Practices & the Green Revolution

🌾 The Green Revolution (1950s–1970s)

Major shifts:

  • Human/animal labor β†’ Machinery

    • Tractors, harvesters, combines

    • Increased efficiency & profit

    • Higher fossil fuel use

  • Polyculture β†’ Monoculture

    • Growing a single crop on large areas

    • Increases yields but reduces biodiversity

  • Natural fertilizers β†’ Synthetic fertilizers

    • N–P–K (Nitrogen, Phosphorus, Potassium)

    • Boosts productivity but contributes to eutrophication and soil degradation

  • Rain-fed agriculture β†’ Irrigation

  • Natural pest control β†’ Pesticides

🏞 Land Use & Population Growth

  • Large population increases require more land for food production.

  • Example from slides: U.S. has lost 95% of native prairies (358 million acres lost) due to agriculture.

  • Grasslands provide ecosystem services:

    • Soil formation & protection

    • Carbon storage

    • Water filtration

    • Habitat for biodiversity

🏚 Land Degradation Example: Sahel (North Africa)

  • Traditional: shifting agriculture + grazing + fallow periods

  • Population growth β†’ land farmed continuously β†’ nutrients depleted

  • Overgrazing removed vegetation β†’ desertification

  • Soil erosion & loss of food production

5.4 β€” Tilling, Slash & Burn, and Fertilizers

🚜 Tilling

  • Mechanical mixing of soil (plowing, harrowing)

  • Pros:

    • Breaks up soil

    • Helps plant seeds

  • Cons:

    • Increases erosion

    • Reduces soil organic matter

    • Releases stored carbon β†’ contributes to climate change

πŸ”₯ Slash and Burn Agriculture

  • Cut vegetation β†’ burn β†’ plant for a few years β†’ leave fallow

  • Adds nutrients short-term (ash)

  • Sustainable only with low population density

  • Problems:

    • Deforestation

    • Loss of biodiversity

    • Soil quickly loses fertility

    • Contributes to climate change

🌱 Fertilizers (N-P-K)

  • Industrial fertilizers = blend of:

    • Nitrogen β†’ leaf growth

    • Phosphorus β†’ root development

    • Potassium β†’ overall plant function

  • Problems:

    • Runoff β†’ eutrophication/algal blooms

    • Nitrogen contributes to greenhouse gases (Nβ‚‚O)

5.5 β€” Irrigation Types, Benefits, Drawbacks

πŸ’§ Types of Irrigation

1. Flood Irrigation

  • Field is completely flooded

  • 20% water loss (evaporation/runoff)

  • Cheap but leads to waterlogging

  • Flood irrigation: involves flooding an agricultural field with water. This system sees about 20% of the water lost to evaporation and runoff. This can also lead to waterlogging of the soil.


2. Furrow Irrigation

  • Trenches between rows filled with water

  • 33% water loss

  • Cheap, low-tech

  • Uneven water distribution

  • Furrow irrigation: involves cutting furrows between crop rows and filling them with water. This system is inexpensive, but about 1/3 of the water is lost to evaporation and runoff.

  • Drip irrigation: a more efficient method that delivers water directly to the roots of plants, minimizing evaporation and runoff losses.

3. Spray Irrigation

  • Groundwater pumped through sprinklers

  • 25% or less water loss

  • Efficient but expensive + requires energy

  • Spray irrigation involves pumping groundwater into spray nozzles across an agricultural field. This system is more efficient than flood and furrow irrigation, with only 1/4 or less of the water lost to evaporation or runoff. However, spray systems are more expensive than flood and furrow irrigation, and also requires energy to run.


4. Drip Irrigation

  • Tubes drip water directly to roots

  • Only ~5% water loss

  • Most efficient

  • VERY expensive β†’ rarely used in developing nations

  • Drip irrigation uses perforated hoses to release small amounts of water to plant roots. This system is the most efficient, with only about 5% of water lost to evaporation and runoff. However, this system is expensive and so is not often used.



5. CENTER PIVOT

  • Β A method that uses rotating sprinkler systems to water crops efficiently, allowing for uniform distribution of water across large fields.

  • Drip irrigation: A highly efficient technique that delivers water directly to the roots of plants through a network of tubing, significantly reducing evaporation and runoff, but often requires a higher initial investment.

β›” Problems with Irrigation

1. Waterlogging: occurs when too much water is left to sit in the soil, which raises the water table of groundwater and inhibits plants’ ability to absorb oxygen through their roots.

  • Water saturates soil

  • Roots can’t absorb oxygen

  • Crops die

2. Salinization

  • Irrigation water evaporates β†’ salts remain in soil

  • Over time, soil becomes toxic to plants

  • Examples: Australia, California, Arizona

3. Aquifer Depletion

  • Overdrawing groundwater

  • Ogallala Aquifer (U.S.) is severely depleted

  • Takes thousands of years to recharge

  • When irrigation comes from rivers and groundwater which is saltier than rainwater, the salts in remain in the soil after the water evaporates. The result is salinization. Over time, salinization can make soil toxic to plants.


    This negatively impacts agricultural productivity and can lead to a further decline in crop yields, threatening food security in the region. To combat salinization, it is essential to implement sustainable irrigation practices, such as drip irrigation, crop rotation, and the use of salt-tolerant plant varieties.


🌡 Arizona FRQ Example

(a) Why choose furrow irrigation in Arizona?)

  • Cheap

  • Low-tech

  • Good for large fields

  • Farmers may not afford spray/drip systems

(b) Why not flood irrigation?)

  • High evaporation in dry/arid climate

  • Wastes water

  • Can lead to salinization

  • May cause waterlogging in low areas

5.6 β€” Pesticides, GMOs, and Regulations

πŸ› Types of Pesticides

  • Herbicides – weeds

  • Fungicides – fungal diseases

  • Rodenticides – rats/mice

  • Insecticides – insects

Benefits:

  • Higher yield

  • Less crop damage

πŸŒ€ Pesticide Treadmill

  • Pests evolve resistance

  • Farmers use more or stronger pesticides

  • Causes:

    • Resistance

    • Environmental damage

    • Bioaccumulation & biomagnification

  • Leads to greater pesticide use over time

🌽 GMOs (Genetically Modified Organisms)

Benefits

  • Increased resistance to:

    • Pests

    • Drought

    • Disease

  • Higher yield

  • Reduced need for pesticides (e.g., Bt corn)

Drawbacks

  • Loss of genetic diversity

  • Cross-pollination may harm wild species

  • Controversial public perception

  • Patented seeds β†’ expensive for farmers

βš– Delaney Clause (1958 Amendment)

  • A part of the Food, Drugs, and Cosmetic Act of 1938

  • States:

    Any additive that causes cancer in humans or animals cannot be added to food.

  • Zero-tolerance policy for carcinogenic additives

πŸŒͺ Dust Bowl (1930s)

  • Caused by:

    • Drought

    • Over-plowing

    • Removing native grasses

  • Led to:

    • Massive wind erosion

    • Crop failures

    • Migration from Great Plains

β›° Weathering vs. Erosion

  • Weathering: breaking down of rock where it is

  • Erosion: movement of rock/soil from one place to another