37-52 Irrigation, agriculture, and pest control

APES 2024

Contour farming

Contour farming

plowing perpendicular across a hill
- Prevents rills and gullies

Terracing

Level platforms cut into steep hillsides
This “staircase” contains water

Perennial crops

• Crops that live year round

• Harvested multiple times

• Longer and more established roots

• Prevents bare soil after harvest

Shelterbelts (windbreaks)

rows of trees planted along edges of fields
- Slows the wind
- Can be combined with intercropping

Conservation tillage

reduces the amount of tilling
-Leaves at least 30% of crop residues
in the field

No-till farming

disturbs the soil even less

Crop rotation

growing different crops from one year to the next
- Returns nutrients to soil
- Prevents erosion, reduces pests
- Wheat or corn and soybeans
- Pests usually prefer one crop

Intercropping (strip cropping)

planting different crops in alternating bands
-Increases ground cover
-Replenishes soil
-Decreases pests and disease

Ways to improve soil fertility

include crop rotation and using green manure and limestone

Limestone

base will neutralize acids in soil, raises pH so soil is more basic than acidic

Rotational grazing

regular rotation of livestock between different
pastures in order to avoid overgrazing in a particular area

Green manure

Leftover plant matter from a cover crop

Seed banks

institutions that preserve seed types as living museums of genetic diversity
Seeds are collected, stored, and periodically planted

Norway Doomsday Seed Vault

stores millions of seeds from around the world

Pest

any organism that damages valuable crops

Weed

any plant that competes with crops

Pesticide

poisons that target pest organisms

Examples of pesticides

• Insecticides = kill insects

• Herbicides = kill plants

• Fungicides = kill fungi

• Rodenticide = kills rodents

Some individuals are genetically immune to a pesticide

They pass these genes to their offspring

Pesticides can

stop being effective

Pesticide treadmill

chemists increase chemical toxicity to compete with resistant pests

Pesticides also kill

nontarget organisms (Including predators and parasites of pests, Pest populations become harder to control)

Gene for pest resistant trait is added to the plant through

Genetic modification

GMO ex.

Bt corn with bacteria that produces Bt crystals toxic to pests

Roundup ready crops are modified to be resistant to

Roundup so weeds are killed and not crop (Monsanto lawsuit)

Integrated Pest Management (IPM) Techniques to suppress pests:

• Biocontrol

• Chemicals, if necessary

• Population monitoring

• Habitat alteration

• Crop rotation and transgenic crops

• Alternative tillage methods

• Mechanical pest removal

• Intercropping

IPM in Indonesia increased rice yields

13% and saved $179 million/yr in phased-out subsidies

Biological control

uses a pest’s predators to control the pest
- Reduces pest populations without
chemicals
- Reduces chemical use

Biological control examples

• Cactus moths control prickly pear

• Ladybugs for aphids

• Parasitic wasps for caterpillars

The effects of an introduced species are

unpredictable (risky)

Introduced species may have

“nontarget” effects on the environment and surrounding economies

Removing a biocontrol agent is harder

than halting pesticide use

Biocontrol use must be

carefully planned and regulated

Biocontrol benefits

• Reduces death and mutation of nontarget species

• Less dangerous health effects on humans

• Less contamination of surface and ground water

Not all insects are

pests

Pollinator examples

• Hummingbirds

• Bats

• Insects (bees, wasps, etc.)

Flowers are evolutionary adaptations to

attract pollinators

Colony collapse disorder

entire beehives have vanished

Cause for colony collapse disorder

is unknown (Insecticides? Parasites? Stress?)

Ways to preserve bees

Reducing or eliminating pesticide use and planting
flowering plants

Bees pollinate over

100 crops and contribute $15 billion in services/year