Layers of soil (soil horizons) soil profile

• Surface litter – fallen leaves and partially decomposed organic matter

• Topsoil – organic matter, living organisms, and rock particles

• Zone of leaching - dissolved or suspending materials moving downward, minerals may leach quickly and deprive plants of nutrients

• Subsoil – larger rock particles with organic matter, and inorganic compounds

• Weathered parent material – rock that has undergone weathering

• Bedrock – solid rock layer

Topsoil is richer in organic matter than the other soil layers; without it plants cannot grow

Particle size increases down

Soil Characteristics• Color– Darker soils means richer in humus and nutrients– Use as indicator of soil’s fertility

• Texture– Based on particle size• Clay, silt, and sand (smallest to largest)• Loam – even mixture of the 3 particle sizes

– Influences workability because of how porous it is• Finer the particle size, less space and harder for air

and water to travel through• Silty soil or loamy material is best for plant growth

Soil Characteristics (continued)

• Structure– Arrangement of particles – “clumpiness”– Clumpy soil has more humus and is more rich in

nutrients– Too clumpy may prevent plant roots from

growing• pH– Plants die if soil is too acidic or too alkaline– Acid precipitation and leaching can affect pH

Learning Target• To understand ways to prevent soil

degradation and why they will prevent soil degradation

Land degradation occurs when human activity or natural processes damage land so that it can no longer support plant growth or other ecosystem services

Erosion

• #1 cause of land degradation• Can help create soil through deposition• Takes away the topsoil• Humans cause this through overgrazing,

clearing forests on slopes, clear-cutting, and leaving soil bare after harvests

Farming Practices for Soil Conservation

• Plants slow wind and water– roots hold soil in place and absorb water

• Intercropping• Crop rotation• Cover crops• Shelterbelts• Conservation tillage• Terracing• Contour farming

• soil conservation

Intercropping

– Planting crops in mixed arrangements– More plant cover– Less vulnerable to insects and disease

Crop rotation

• Alternate crops grown in a field• Returns nutrients to soil• Breaks disease and pest cycles• Prevents erosion