4 Soil Formation, Soil Erosion, & Pollution

What are soils made of?

living and non-living matter

What two processes form soils?

Physical and chemical weathering

What materials add to soil from the air?

Dust, nutrients, nitrogen compounds

What are the five soil-forming factors?

Climate, rock, organic matter, slope, time

What does parent rock control?

Grain size and nutrients

Which factor affects soil fertility most?

Climate

Where do the most fertile soils form?

Moderate rainfall regions

What are the world’s most productive soils?

Mollisols

What type of soil forms in wet equatorial regions?

Laterites

What are laterites rich in?

Aluminum

Are laterites fertile or infertile?

Infertile

What US region’s soils are shaped by forest processes?

Eastern US

What vegetation dominates the central U.S.?

Grasses

What type of soil did ancient Amazonians create?

Dark earth

What was once assumed about Amazon soils?

Too poor for civilizations

What activities made Amazonian soils fertile?

Burning and organic waste spreading

What is a “chronosequence”?

Soils differing only by age

How thick is the active soil layer?

About one meter

What is lost with erosion?

Nutrients and topsoil

What pollution does erosion cause?

Water turbidity

What farming practice increases erosion?

Tilling

What practice helps reduce erosion?

No-till agriculture

What has increased over time?

Food yield per area

Major soil threats per Carson?

Pesticides, herbicides, arsenic