Soil Introduction

Soil is formed over a VERY long period of time.

As solid rock is weathered into tiny pieces as a result of:◦ freezing and thawing◦ having water wash over it by rivers and waves◦ glaciers moving across rock

The tiny fragments of rock form the first layer of soil. As the layer becomes thicker and thicker, soil beings to form.

What is Soil?

Soils can take hundreds, thousands, to millions of years to form.

The type of soil that will form is dependant on the climate, location, vegetation and time.

It is also dependent on the parent material, which is the rock that the soil forms from.

Formation of Soil

Soil is composed of 4 main things:1) Minerals – tiny

fragments of rock2) Air3) Water4) Organic Matter –

leaves, roots, and small living organisms.

Composition of Soil

The organic matter is the main source of food for plants growing in the soil.

The air is found in the spaces between the mineral matter and help the plant roots to breathe.

Water is used by the plants and helps to move food to the roots.

Soil is an important resource as majority of food sources (other than aquatic) are traced back to soil.

Think of a hamburger and all the ingredients, how many can be traced back to soil?

Soil is considered non-renewable because it takes so long for productive soil to be formed.

Even though soils can be very deep, the most important part is the surface, 15-30 cm down.

This portion is called topsoil and will be most likely dark in colour, almost black.

The dark colour shows that there is a lot of organic matter present.

Even if fertilizer is added to a poor top soil ,the plants will still not grow to full potential.

Soil Profiles

Subsoil is the next layer below the topsoil. It is usually lighter in colour. Fewer living things are here because there

is less organic matter and food for plants. Under the subsoil is the parent material. This is made of rock, dust and gravel. There are no living things in this layer, as

there is no organic matter. Formed as the bedrock underneath breaks

down.

Horizons – typically there are 4.

O-horizon: leaf litter and organic material.

A-horizon: Top soil B-horizon: Sub soil C-horizon: Parent

material R-horizon: Bed Rock

Soil Profile

The soils that agriculture has been using have been there for thousands of years.

When land is first cleared and planted, the soil is typically very rich in nutrients and organic matter. Crops and plants will grow well here.

However, as time passes and more crops are planted, the soil becomes poor.

This means it loses some of the organic matter present and produces less and less food.

Soil Degradation

These plots were eventually abandoned and more plots were cleared.

The abandoned plots were left uncovered and unprotected. This creates soil degradation.

Soil degradation is the wearing out of soil. As soil derogates, it loses it’s ability to grow

food/forests and support livestock/wildlife.

Salinity is a type of soil degradation.

Salts build up in the soil. They appear as white patches

on the soil. Salt can be deposited at the

top of the soil due to the water underneath. As salty water is pushed to the surface and evaporates, salt is left.

High uses of potassium fertilizer can cause soil salinity.

Salinity

Solutions to Soil Salinity: Keep plots

watered. Stop using

fertilizers.

Today our soils contain about half the amount of organic nutrients that they used to contain.

This is due to clearing areas for agriculture, taking away natural plants and forests.

By constantly planting crops and not allowing soils to ‘regenerate’, organic matter loss only increases.

Too much tillage can also cause a loss in organic matter as it disturbs the natural plant life.

Organic Matter Loss

Growing grasses and alfalfa (crops called forages) allow nutrients to be added back to the soil.

Adding natural fertilizer, such as manure.

Solutions to Organic Matter Loss

When a strong wind blows on bare soil, loose material is blown away.

Most of this material will accumulate in other areas, such as along fences or in ditches.

Lighter soil material is lost as dust into the atmosphere.

If too much soil is blown away, any plants growing there will be damaged, some beyond repair.

Wind Erosion

The best way to prevent soil erosion is to keep soil surface covered.

Soil can be covered with grass, straw, stubble, trees or a crop to protect it from the wind.

By not tilling soil (mixing soil) in the fall, which is typically windy, leaves more soil behind.

Continuous Cropping – Never allowing a field to be bare, always having a crop growing there.

Shelterbelts – Rows of trees to slow the wind.

Strip-cropping – Seeding narrow strips of crops prone to erosion, such as sugar beets, alternating with strips of crops that are erosion resistant, such as wheat.

Solutions to Wind Erosion

Water erosion occurs anytime water flows across bare soil.

This is especially apparent on a steep or long hill.

Water Erosion

1) When raindrops fall, they tend to explode out, like a bomb – called splash erosion, and the 1st step in water erosion.

2) After rainfall continues, water begins to run down the hill and will pick up pieces of soil with it and wash them away – called sheet erosion and is the 2nd step in water erosion.

3) If the rain continues for a long period of time, small paths will be cut in the soil, creating tiny rivers – called rills and are the 3rd step in water erosion.

Steps to Water Erosion

Soil can be protected from rain by keeping it covered with straw, grass, stubble or crops.

Rows of crops can be planted across the slope of a hill.

Solutions to Water Erosion

The packing down of soil by forces of weight on the surface.

It occurs when heavy equipment (such as trucks and farming equipment) travels across the soil again and again.

Compaction will slow or prevent good root growth.

Compaction

Stop driving the equipment over the soil (duh!)

Tilling up the compacted soil and replanting will allow nutrients to be added and soil to become more aerated.

Solutions to Compaction

Occurs when unwanted chemicals build up in the soil.

Main cause is the overuse of pesticides. This causes ‘Non-point source pollution’, a

type of pollution where the exact source cannot be pinpointed.

The leaching and traveling of these pesticides can end up in places such as drinking water reserves and rivers

Soil Pollution

Use only organic pesticides or release insects that will combat the pest you are trying to get rid of.

Create reservoirs around the property to catch any run off.

If pesticides must be used, regulate amounts.

Solutions to Soil Pollution

When land gets so worn out from farming or soil erosion over time, it will turn into a desert waste land.

It is not longer viable for plant growth.

This usually occurs where long areas of drought have taking place, such has countries in Asia and Africa.

Desertification

Allowing land to ‘rest’ and rejuvenate over many years.

Irrigating land and planting nutrient adding crops, such as grasses.

Solutions to Desertification