Soil Structure and Fertility

What is Soil

• Naturally occurring, loose material at the surface of the Earth

• Supports plant and animal life• Composed of: solid, liquid and gas

Solid Components of Soil

• 50% of the volume of soil• Creates pores that are occupied by liquid and gases• Made of mineral and organic matter

– Mineral portion – made of large and small grains of sand, clay, silt

– Organic matter (aka humus) – dead plant and animal remains that are broken down by living soil organisms

– Helps to hold water– Has a major role in the fertility of the soil– Keeps soil loose so roots have room to grow and organisms

can breath

Pore Space

• How tightly packed the soil is together

Liquid and Gas Components of Soil

• 50% of soil volume is the space between the individual grains of soil and is occupied by liquid and gases

• Water acts as the main way that nutrients are made available to plant roots

• Air in soil allows for oxygen to get to organisms that live in the soil

• The pore space between grains allows carbon dioxide produced by organisms living in the soil to escape

Types of Soil

• Depends on the mixture of sand (largest particle), silt (intermediate size), and clay (very fine particle)

Soil LayersO Horizon – organic layer of soil, made of leaf litter and humusA Horizon – topsoil, made of humus and mineralsE Horizon – eluviation layer, made of sand and silt, has lost most of its minerals and clay as water drips through the soilB Horizon – subsoil, contains clay and mineral deposits from above layersC Horizon – regolith, it is slightly broken-up bedrockR Horizon – unweathered bedrock

O HorizonA Horizon

E Horizon

B Horizon

C Horizon

R Horizon

Maintaining Soil Structure and FertilityWhat can be done?

1. Contour plowing – plowing across the slope of a hill forms ridges (can be created with soil or vegetation) that help prevent soil from washing down a hill

2. Use organic matter (biological material in the process of breaking down) to restore nutrients to the soil; such as compost, animal manure or humus

Continued3. No-Till Farming – seeds for the

next crop are plants straight through the remains of the previous crop (crops that are leftover from previous years provide nutrients for the soil), also reduces compaction of soil

4. Adding mulch – such as leaves or grass clippings to the top of soil can control weed (an unwanted plant) growth (and provide nutrients for the soil)

Continued

5. Cover crops – crop grown for the protection and enrichment of the soil– Planting diverse cover

crops – each plant grown as a cover crop provides a different nutrient, planting a diverse crop allows different nutrients to be added back to the soil

Continued

6. Adding lime – raises the pH (brings it closer to neutral)

7. Crop rotation – the practice of growing different crops in the same area in different seasons– helps to avoid problems with

disease, soil dwelling insects and depleting soils of nutrients specific plants require