APES Unit 5.5 Irrigation Methods

Practice FRQ (3 sentences minimum)

★ Describe how soil salinization occurs. Propose a solution to prevent or remediate soil salinization. Identify one disadvantage of the solution you propose.

Soil salinization occurs when over time, evaporation of water leaves behind naturally occurring salt in groundwater. This can reach toxic levels and stunt plant growth by dehydrating roots. This can be solved through drip irrigation, but it is incredibly expensive.

Use of Irrigation Water

Water is transferred to particular locations that need more rainfall

• 70% freshwater = irrigation

• US = 1/3 of freshwater

Two Main Sources of Irrigation Water

1. Groundwater

2. Aquifers

Where is Groundwater Stored?

in Aquifers: Pore spaces within permeable rock layers underneath soil

Unconfined Aquifer

Porous rock covered by soil

• Water easily flows

• Direct/rapid connection with surface

  • More likely contaminated by anthropogenic chemicals

Confined Aquifers

Surrounded by layer of impermeable rock or clay to impede water flow to/from aquifer

• Water Recharge: Slower = water is older + less likely contaminated

  • Withdrawal not balanced by recharge

Groundwater Recharge

Process where precipitation percolates thru soil into groundwater

Two Ways of Aquifer Depletion

1. Saltwater Intrusion: Excessive pumping of water reduces pressure → saltwater seeps into groundwater

2. Cone of Depression: Excessive pumping dries nearby wells

   1. Slow Rate of Recharge: Can’t keep up w/ withdrawal

3 Main Ways of Water Usage

Water footprint: Total daily per capita use of fresh water for country

1. Industrial

2. Municipal

3. Agricultural

• Always in high demand = Freshwater Scarcity

Furrow Irrigation

Farmer fills trenches along crop rows with water

• Easiest

• Inexpensive

• 67% efficient: 33% run off or evaporates

Flood Irrigation

Floods field w/ water to soak crops evenly

• ex. Diverting river/stream

• ex. pumping water thru pipe to field

— Increases Waterlogging: More disruptive

• 80% efficient

Spray Irrigation

Water pumped into apparatus w/ many nozzles that spray water across field (“Giant law sprinklers”)

• Expensive

• More efficient: Less water loss

Drip Irrigation

Slowly dripping hose on ground or under soil to directly deliver water to roots

• Most Effective: 95%

  • Avoids waterlogging / evaporation

  • Dry topsoil → Reduces weed growth

  • Most Expensive

Waterlogging

Overwatering can saturate soil’s pore spaces w/ water so roots can’t take in needed O2

• Stunts growth / kills plants

• Solution: Drip irrigation

  • Soil Aeration: Poking holes/cores in soil to drain + aerate

Salinization

Process of salt building up in soil over time b/c naturally occurring salt in groundwater is left behind thru evaporation

• Dehydrates plant roots / stunts growth

• Solution: Drip irrigation

  • Soil Aeration: Poking holes/cores in soil to drain + aerate

  • Flushing fresh water

  • Switch to freshwater use