Soil Base Different climates create wet climate or dry climate soils True soil consists of four main parts; if one of these parts is missing, the material cannot be considered soil! Minerals Bacteria & organic materials Air Moisture

Minerals Minerals in soil come from rocks, and are known as parent material Minerals become part of the soil when rock is broken down by weathering into smaller parts (sand, silt, clay) Many of these minerals such as calcium, phosphorous & potassium are nutrients needed for plant growth

Bacteria & Organic Materials When plants and animals die, they decompose with the help of bacteria in the soil As they break down, nutrients are released decaying organic materials form humus, which provides nutrients and moisture for plants; humus gives soil its dark colour

Air All living beings need air to function Plants also need air around their roots A high humus level (amount of decomposing animals, plants and leaves) in the soil is helpful because this creates air pockets in the soil Air spaces are also created by worms, insects and small animals that tunnel through the soil

Moisture Water dissolves nutrients in the soil and plants take them up through their roots Water is also necessary for weathering rock and the decay of organic materials

How Soil is Formed Essentially, new minerals are added at the bottom through the weathering of the parent material, while organic materials are added at the top simultaneously The top layer of soil containing humus is called topsoil and takes a long time to form

Loam A well-balanced mixture of sand, silt, clay and humus is called loam This is the best soil for growing plants because it encourages root growth, holds moisture and allows water to pass through at a rate moderate enough to allow plants to take up nutrients

Leeching This happens in areas where there is a great deal of precipitation Continual downward movement of water through the soil dissolves the chemical nutrients in the soil and carries them away This removes the nutrients that the plants need In very wet climates, leeching can take water-soluble minerals so deep that plant roots cannot reach them You can identify leeched soil by it’s poor, thin topsoil layer Leeched soil can be developed into excellent farmland by adding fertilizer

Calcification Occurs in drier climates; when the water in the topsoil evaporates, water from below is drawn up to replace it This process is called capillary action The water drawn to the surface evaporates, leaving behind minerals that were dissolved in it; the result is a thick topsoil layer rich in minerals (calcium is the main mineral deposited; hence the name) However, in very dry climates, the amount of minerals deposited can be so high that the top layer formed can be poisonous to plants

TOPSOIL PROFILE

LEACHED SOIL PROFILE

CALCIFIED Soil profile