The unknown ecosystem THE DIRT ON SOIL

In your notes…meaning actually write it down!...answer the question below What is soil? What is it made of? Where do we get if from? What is your “definition” of soil

WHICH IS LARGER? The number of organisms in one shovelful of soil The number of humans on earth

SOIL CREATURES More in one shovelful than all the humans that have ever lived on earth Many don’t even have names yet

A Recipe for Soil Start with minerals Add organic materials (humus) Water Air

Soil Characteristics It takes 100 to 100,000 years to form one meter of soil Soil forms by weathering and decomposition. Faster in warmer climates Why?

Physical Composition of Ideal Soil for Crops Mineral (weathered rock) = 45% Air = 25% Water = 25% Organic matter (humus) = 5%

HUMUS Dark organic matter from decomposed plants and animals Provides nutrients for crops Soil organisms feed on it Absorbs and holds water

SOIL DECOMPOSERS: BACTERIA 1000 fit on the head of a pin. Divide to reproduce every 20 minutes.

BEETLE MITES Arachnids No eyes (it’s dark in the soil) Eat only fungus

NEMATODES Also called round worms Only 1 mm long Some eat bacteria, some eat detritus, some eat fungus

Centipedes, millipedes, snails, slugs

EARTHWORMS Live 3 to 6 years Eat detritus, also swallow soil Add bacteria back to soil Aerate soil

Tardigrade

Soil Organisms https://www.youtube.com/watch?v=VuHznslr8aI https://www.youtube.com/watch?v=YF8OJt_pujc https://www.youtube.com/watch?v=cjV2WP0wkvo

The texture is caused by the size of the soil particles SOIL TEXTURE The texture is caused by the size of the soil particles

Soil Texture (Sand) Sand – Between 0.06-2.0 mm in size Sandy soil drains quickly 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.

Soil Texture (Silt) Silt – Between .002-.05mm in size. Need microscope to see Silt allows for air to circulate but still retains some water. Silty soils do not usually hold enough water for most plants.

Soil Texture (Clay) Clay - < .002 mm in size. Water clings to tiny particles holding larger soil particles together forming clumps called aggregates. Aggregates like gravel provide drainage channels for water. Water will not drain in soils with a lot of clay. Clay is easily compacted, crushing air and water pore space. Plants root cannot penetrate through dense clay soils. Clay is a poor material to build on because it swells with water.

Loam Loam is soil with a mixture of sand, silt and clay. It is the best type of soil for most crops