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Soil Composition
(pages 211 – 216 Environmental Science)
Soil - a mixture of ____________, ______________, ______________, ______________
 One meter of soil takes __________________ year to form? Why?
 Soil forms by ______________ (minerals) and ______________ (humus)
 Forms quicker in warm moist climates
Physical composition of an ideal soil for crops
 Minerals – _____% - (see texture)
 Air filled pore space – _____%
 Water filled pore space – _____ %
 Organic matter (humus) _____%
Humus –
It provides nutrients for crops. Many organisms feed on and decompose organic matter making
the nutrients available for plants.
It _________ and ______ water which is needed by plant roots
Texture –
Sand – Between ___________ mm in size
Sandy soil drain ___________ so roots can penetrate. Too much sand in a soil does not hold
enough water and nutrients for most plants.
Does not shrink or swell so it makes a good foundation for buildings.
Silt – Between _____________ mm in size
Silt allows for air to circulate but still retains some water. Silty soils do not usually hold enough
water for most plants.
Clay - < ____________ in size – Water clings to tiny particles holding larger soil particles
together forming clumps called ______________(see drawing). Aggregates like gravel provide
drainage channels for water. Water will not drain in soils with a lot of clay. Clay is easily
______________ crushing air and water pore space. Plants root cannot penetrate through dense
clay soils.
Clay is a poor material to build on because it _________________________ with water.
______________ - A soil with a mixture of sand, silt and clay. It is the best type of soil for most
crops