Irrigation Methods (College Board AP® Environmental Science): Study Guide

Freshwater is essential for human survival, agriculture, and industry

• Freshwater only makes up only about 2.5% of the Earth's total water supply

The largest use of freshwater is for irrigation (70%)

• Irrigation supports global food production by ensuring crops receive adequate water, especially in arid and semi-arid regions

Types of irrigation include:

• Furrow irrigation

• Flood irrigation

• Spray irrigation

• Drip irrigation

Other major uses include:

• Industry (20%): Used in manufacturing, cooling, and processing in sectors such as power generation, textile production, and food processing

• Domestic use (10%): Drinking water, sanitation, and household needs, including cooking, cleaning, and personal hygiene

Human activities alter natural freshwater systems, affecting availability and quality of freshwater due to overuse, pollution, and climate change impacts

Waterlogging occurs when excess water saturates the soil, preventing proper drainage

• This raises the water table, reducing air spaces in the soil and limiting oxygen availability to plant roots

Causes:

• Over-irrigation, especially in poorly drained soils

• Heavy rainfall with inadequate drainage

• River or groundwater flooding

Effects on plants:

• Oxygen deficiency: Roots cannot perform respiration properly

• Nutrient uptake issues: Leads to yellowing leaves, stunted growth, and root decay

• Increased susceptibility to disease

Prevention and solutions:

• Improve drainage systems (e.g., installing pipes, ditches)

• Use raised beds or furrow irrigation in water-prone areas

• Grow water-tolerant plant species in high-risk zones

How it works: Trenches (furrows) are dug between crop rows and filled with water, which seeps into the soil

Water loss: About 1/3 (30%) of the water is lost to evaporation and runoff

Benefits:

• Low-cost system: Simple and inexpensive to implement

• Minimal energy requirement: Does not require complex infrastructure

Drawbacks:

• High water loss: Inefficient compared to other methods

• Uneven water distribution: Some plants may receive more water than others

• Increased risk of soil erosion and salinization

How it works: Water is released to flood entire fields, allowing it to soak into the soil

Water loss: About 1/5 (20%) of the water is lost to evaporation and runoff

Benefits:

• Simple and inexpensive: Requires minimal infrastructure

• Effective for flat fields: Best suited for crops like rice that thrive in standing water

Drawbacks:

• High water usage: Inefficient compared to modern systems

• Waterlogging risk: Excessive water can raise the water table and suffocate plant roots

• Soil degradation: Increases salinity if water evaporates and leaves mineral deposits

How it works: Water is pumped through pipes and sprayed over fields using rotating nozzles or sprinklers

Water loss: About 1/4 (25%) or less of the water is lost to evaporation and runoff

Benefits:

• More efficient than flood and furrow irrigation

• Can be used on uneven terrain where other methods are impractical

Drawbacks:

• High cost: Requires expensive equipment and installation

• Energy-intensive: Needs pumps and pressure systems to operate

How it works: Perforated hoses release small amounts of water directly to plant roots

Water loss: Only about 1/20 (5%) of the water is lost to evaporation and runoff

Benefits:

• Most water-efficient method, reducing waste

• Minimizes soil erosion and prevents waterlogging

• Improves crop yield by delivering precise amounts of water to roots

Drawbacks:

• Expensive to install and maintain

• Not widely used due to high initial costs

• Requires regular maintenance to prevent clogging of hoses