5.3.1: Soil Degradation & Conservation

Big Pic

Importance of soil:

• Filters water

• Carbon sink

• Grows essential plants/food

• A living system (ecosystem + system)

Human activity has increased soil degradation

• has exposed soil: open to soil loss

• global issue regardless of economic status

The Dust Bowl: 1930s

Caused by poor farming methods, wind, drought

Land was overworked (overgrazed + plowed), topsoil was gone, soil exposed—> wind heavily eroded it —> dust storms

Costs: no crops, loss of topsoil, starvation, respiratory diseases, death (pneumonia), loss of livelihood, increased urban pop. (but less jobs)

Results: investment into soil studies

• 1935: US soil erosion act (encourage soil conservation practices

Ecological Succession

Changes in vegetation overtime after a disturbance

• r-strategists (plants) come first and add nutrients to the soil

What makes soil good for growing?

Water retention

Nutrients (returns to soil as OM breaks down)

OM provide sufficient moisture + structure to support drainage

Nitrates, phosphates, potassium

pH affects plant growth + mineral availability (ideal 5.5-7.5)

Role of Succession on Fertility

Primary vs Secondary Succession

• Primary: no soil is present; succession on bare rock (ex: lava flow, rock exposed after glacial movement, abandoned parking lots)

• Secondary: succession on soil after removal by nature or humans (forest fire, clear cutting, flooding, agricultural land)

Biological Processes

• Living things breaking down OM into nutrients

• Decomposers

  • bacteria breaks down waste —> puts nutrients back into soil

  • invertebrates eat, digest, excrete (mix OM into soil)

• Nitrogen fixing bacteria

  • absorb N2 gas from atm and converts it into nitrates

Biological Transformations into the Ecosystem

Nitrogen fixation done by microbes in the soil

• N2 gas —> NH3

• legumes and bacteria have a mutualistic relationship

• creates 10% of what a plant needs

• ammonification by decomposition

Nitrification

• NH4 (ammonia) —> NO3 (nitrate)

Contributes to plant growth, like soil fertilizers do

Soil = non-renewable

Rate of formation > rate of degradation

1000 yrs to make 5 cm

• varies by climate

  • hotter + wetter —> faster decomposition + max plant growth —> faster formation

Not replaceable in a human’s lifetime