Topic 5.1: Introduction to soil systems Starter: What is soil? Why is soil so important? Where does soil come from?

Soil is a complex ecosystem Minerals (Rocks) Organic material (Humus) Gases (Air) Liquids (Water) The exact mix of these four portions give soil its characteristics. In addition there are also: Many plants and animals (and micro-organisms)

The majority of food we consume depends ultimately upon soil.

“Too many people have lost sight of the fact that productive soil is essential to the production of food” Hugh Hammond Bennett was a pioneer in the field of soil conservation. He was convinced that soil erosion was a serious problem facing the planet. It reduces areas in which crops can be grown.

Soil systems are dynamic Many complex systems are interlinked Water cycle Nutrient cycles (e.g. Nitrogenous compounds)

Soil Horizons Using the help sheet create your own soil profile diagram and describe each of the horizons. You do not need to know their names, but you do need to know the letters.

Soil Horizons O Horizon: New deposited organic matter is being broken down (decomposed) by a variety of different organisms.

Soil Horizons A Horizon: Build up of humus. Partially decomposed organic matter and fine mineral particles. Dark layer or brown or black organic material – humus layer Water-logged soils have reduced decomposition

Soil Horizons E Horizon: Less humus and more inorganic minerals.

Soil Horizons B Horizon: Clay and Iron salts deposited in this horizon. Soluble minerals and organic matter deposited from layer above

Soil Horizons C Horizon: Mainly weathered rock

Soil Horizons R Horizon: Parent or bed rock

This is known as leaching. Water carries particles up or down the layers - translocation In colder, wet climates water flows down into the soil, dissolving minerals and transporting them downwards. This is known as leaching. P>E In hot, dry climates precipitation is less that evaporation (P<E). This means that water moves up through the layers. As water evaporates it leaves the minerals behind, this is called salinization. Can also happen with irrigation.

What type of soil? 20% Clay, 40% Silt, 40% Sand

Loam soils are best for agriculture Sand ensures good drainage and good air supply Clay retains the nutrients Silt hold the sand and clay together and make the soil easier to work with

Porosity – The space between the particles Permeability – The ease at which gases and liquids can pass through the soil Clay soils – High porosity (macropores), low permeability, high nutrients but inaccessible. Sandy soils – High porosity (micropores), high permeability Loam soils – Best of both

Soil sustainability Non-renewable recourse 1 tonne ha-1 yr-1 = 0.05-0.1mm NPK – needs to be replaced