AP Environmental Science Unit 5 Study Guide

Green Revolution (Industrial Agriculture) 

Green Revolution: Shifts towards industrial scale farming via mechanization, synthetic fertilization, pesticide use, irrigation, and increased crop varies. 

• Benefits: Increased yields, decrease world hunger, increase world’s carrying capacity, average costs of production fall as output increases, increased profits for farmers, short term increase in land productivity 

• Drawbacks: Destroys nutrients, excess fertilizer, release of particulate matter, high water need, higher energy demand, soil erosion, pest vulnerability

Mechanization: Increased yields and profits but emits GHGs and compacts soil which decreases water holding capacity. 

Synthetic Fertilizers: Increases yield and profits by directly inputting key nutrients but causes eutrophication and the production of fertilizers releases carbon dioxide. 

Pesticides: Increases yields and profits but can wash off crops in runoff and harm non-target species in local soils and waters. 

High-Yield Variety Crops: Hybrid, genetically modified crops are used to produce a higher yield and some are modified to have extra nutrients as well. 

GMOs: Genetically modified organisms have minimal issues besides the loss of biodiversity as GMOs outcompete native species. GMOs have higher yield, more nutrients, and pest resistance. 

Agricultural Practices 

Monocropping: Growing only one species of a crop. 

• Highly efficient, economical, easy to apply pesticides/fertilizers 

• Decreases biodiversity, increases soil erosion, decreases habitat diversity for species in area, prone to pests 

Tilling: Mixing and breaking up soil to make planting easier, which loosens soil for roots. 

• Loss of root structure, organic matter, and topsoil nutrients

• Increased PM in the air and sediments in nearby water. 

Slash and Burn: Cutting down vegetation and burning it to clear land for agriculture and return nutrients in plants to soil. 

• Done by deforestation: loss of habitat, biodiversity, carbon dioxide sinks 

• Releases carbon dioxide, carbon monoxide, and nitrous oxide; increases PM 

• Lowers albedo, making area warmer 

Synthetic Fertilizers: Puts direct nutrients into the soil without returning organic matter, increasing water capacity, or adding soil decomposers. 

• Leaching: Water carries excess nutrients into groundwater or into surface waters as runoff. 

• Causes eutrophication of surface waters 

Irrigation 

The following is ranked from least to most efficient 

Furrow Irrigation: Trench is dug to align crops and filled with water. 

Flood Irrigation: Floods the entire field, easier but more disruptive to plants. 

• Waterloggs soils and drowns the plants 

Spray irrigation: Groundwater is pumped into spray nozzles 

• Expensive because it requires energy for pumps and movement of sprinklers 

Drip Irrigation: Holes in hose to allow water to slowly drip out 

• Avoids waterlogging and conserves water 

Issues with Irrigation 

Waterlogging: Overwatering can saturate the soil, filling all soil pore space with water. 

• Doesn’t allow air into pores, so roots can’t take in oxygen they need 

• Stunts growth or kills crops 

• Solution: Drip irrigation, soil aeration 

Soil Salinization: Process of salt building up in a soil over time. Groundwater used for irrigation naturally contains small amounts of salt. However, as the water evaporates, the remaining salt accumulates in the soil, causing dehydration and toxicity.

• Solution: Drip irrigation, soil aeration, flushing with fresh water 

Global Human Water Use: 70% of land is used for agriculture - livestock, irrigation etc. So irrigation causes depletion of aquifers and surface water. 

Aquifers and Groundwater 

Groundwater: Water stored in pore space of permeable rock layers.

Aquifers: Useable groundwater deposits for humans. This is replenished by groundwater recharge (percolating down through soil into aquifer). 

Unconfined Aquifer: Water is free to flow in and out, typically near the surface. Recharge quickly. 

Confined Aquifer: Trapped between impermeable layers, preventing water from easily flowing in or out. Its recharge occurs over a long period, as it takes time for water to infiltrate and replenish it.

Saltwater Intrusion: Excessive pumping near the coast lowers water table pressure, allowing saltwater to be introduced into groundwater. 

Cone of Depression: Forms when the water table is lowered by heavy pumping, depleting water and drying nearby wells. 

Pesticides

Broad Spectrum Pesticides: Power pesticides that target entire groups of species of organisms. 

Herbicide: Attack completing plant species. 

Fungicide: Kill fungi. 

Rodenticides: Kills mice, rats, moles, squirrels, chipmunks. 

Drawbacks of Pesticides: 

• Non-Target Deats: Non-target organisms including beneficial predators, pollinators, nitrogen fixers get killed - killing the soil. 

• Bioaccumulation: Pesticides build up in the food chain to toxic levels for birds, fish, and humans. 

• Resistance: Pests become resistant to pesticides due to natural selection. 

• Pollution: Groundwater and aquifer 

• Pesticide Drift: The pesticides end up everywhere. 

The Pesticide Treadmill: Pesticide application → Some pests survive and develop resistance → Resistant pests reproduce and spread → Stronger or more pesticides are needed → More pests develop resistance → Cycle repeats

Meat Production 

Efficiency: Meat production is inefficient as it takes 20x more land to produce the same amount of calories from meat as from plants. 

Concentrated Animal Feeding Operations (CAFOs): Animals are confined and fed antibiotics and nutrient supplements. This uses less land and improves efficiency, but it leads to antibiotic resistance, waste disposal, ethical concerns, poor nutritional content, and emits GHGs. 

Free-Range Grazing: Open grasslands are used for grazing cattle, which takes up a lot of space. Grazing uses less fossil fuels and allows land too dry to farm to be used. Overgrazing leaves land exposed to wind erosion, leading to desertification. This can also lead to pollution of surface waters. 

GHGs and Freshwater as They Relate to Agriculture

Methane: Livestock enteric fermentation and anaerobic rice cultivation both release methane.

Nitrous Oxide: Fertilizers and decay of manure emit nitrous oxide. 

Carbon Dioxide: Slashing and burning and industrial farming emits carbon dioxide. 

Surface Water: Agriculture takes too much water for irrigation and runoff of fertilizers/pesticides are polluting the water. 

Groundwater: Agriculture takes too much for irrigation, fertilizers/pesticides leach into the groundwater, saltwater intrusion, zones of depression. 

Integrated Pest Management 

IPM: A combination of methods used to control pest species while minimizing disruption to the environment. 

Prevention: Crop rotation (growing different crops every season), intercropping (growing different crops together to enhance resilience), resistant plant varieties, and habitat management to reduce pest risks.

Cultural & Mechanical Controls: Mulching, handpicking pests, using traps, and physical barriers like row covers.

Biological Controls: Introducing natural predators, parasites, or pathogens to manage pest populations.

Chemical Controls (Last Resort): Targeted, minimal use of pesticides only when necessary to prevent economic damage.

Drawbacks: Takes more energy and time, may alter the ecosystem, and doesn’t completely eliminate the pests. 

Sustainable Agricultural Practices 

Contour Plowing: Plow and harvest along the contours of land to prevent erosion 

Windbreaks: Plant hedgerows around edges of fields to prevent wind erosion 

Perennials: Do not have to be replanted every year preventing soil disturbance and erosion 

Terracing: Creating stepped levels on sloped land to reduce erosion and improve water retention

No-Till Agriculture: Less erosion and less carbon dioxide emissions though herbicide use may increase

Strip/Intercropping: Planting two or more crops that work synergistically, improving soil health and restores nutrients

Crop Rotation: Reduces specific demands of one crop on soil, prepares solid or next crop, increase nutrient levels

Green Manure Cover (Cover Crops): Organic fertilizer from growing plants that are plowed back into the soil to add nutrients and reduce erosion 

Limestone (Calcium Carbonate): Used to neutralize acidic soil to increase cation exchange capacity. 

Rotational Grazing: Moving animals between pastures to let grass grow back to reduces erosion and desertification and allow plants to develop deep root systems. 

Legumes: Consist of nitrogen fixing bacteria on the roots that put nitrogen into the soil.