Soil - What It Is And What It Does? (1966)

[Music] some people call this dirt but a better name is soil soil is what we usually see plants growing in green plants like grass plants like the tomato plant that Supply food plants with colorful flowers even big plants trees wet soil is mud you may get mud turn your shoes and track it into the house that's not a good place for soil to be much of what we call land or ground is soil when we dig a deep hole we can see that soil has several layers the dark layer at the top is top soil the best part of soil for growing things below the top soil is lighter colored soil mixed with pebbles and large Stones what is soil and where does it come from to find out let's go to a beach there you know there's mostly sand have you ever looked at Sand very closely these are grains of sand they're tiny bits of rock the bits have been broken and worn from bigger rocks containing a mineral called quartz where we find sand we sometimes find clay something like modeling clay bits of dry clay are smaller than bits of sand so small that they feel smooth and powdery Clay comes from granite and certain other kinds of rock how do rocks break into small pieces one way is waves of an ocean or lake rub rocks together knocking off little chips the fast moving water of a river may also rub rocks together knocking off pieces you can see how this happens by shaking stones in water for a long time this rubs the stones together as waves do leaving little chips in the water chips that have been broken from Stones rocks may also be broken down over a very long time by the action of rainwater or by wind that blows sand and Pebbles across larger rocks in winter water may freeze in small cracks in the rock the ice forces pieces of rock to loosen after a long time they're so loose that they easily come off as plants grow on rocks their Roots May loosen bits of the rock that come off so small pieces from different kinds of rock become sand and clay sand and clay are parts of soil what are some other parts this is what is left of a leaf the rest of the leaf has already become part of the soil and this is all that's left of an insect that's being broken down into part of the soil bits of plants and animals make up the dark stuff in soil humus how do sand clay and hum humus get together the wind May mix them the action of rain May mix them in time grass and other plants grow every year some plants die and so do the small animals that live on them all of this becomes part of the mixture this happens for a very long time until the mixture is soil is all soil everywhere in the world like this let's see here's a farm the soil is reddish brown and it seems to have a lot of clay in it here is an orchard in another place this soil is light colored and Sandy a farm somewhere else has darker soil it has lots of humus in it so there are different kinds of soil made up of different mixtures of sand clay and humus to grow plants in any soil water is needed what happens to water that falls on soil here are three different kinds of soil each is in a funnel in a jar this soil is mostly sand when we pour water into it the soil doesn't hold much almost all the water goes right through this soil has lots of clay when we pour water into it the water stays on top very little water soaks into the soil or passes through it this soil has lots of humus water spreads through it the soil soaks up water like a sponge until all the soil is moist in time only a little water passes through which soil do you think is best for growing plants this bean plant is growing in very sandy soil this plant is growing in soil with a lot of clay this plant is growing in soil with lots of humus though some plants grow well in sand or clay many need soil with lots of humus we call this kind of soil LOM but plants need more than LOM to grow big and healthy for example these two plants are both growing in LOM yet this plant looks larger and healthier than the other perhaps something is missing from this soil if so maybe we can make it good for growing plants by putting fertilizer into it fertilizer has important chemicals called minerals minerals and humus are not the only things that can make soil better for plants animals that live in soil may help too for instance earthworms earthworms dig holes letting Water and Air air into the soil also when a worm eats soil passes through its body so worms loosen the soil when it happens to rain the rainwater May easily soak this loose soil rain can do other things to soil and to plants and animals in it let's see what happens to two white gloves left out in the the rain one where grass is growing the other where there is no grass when the rain has ended we see that the glove left where grass is growing is clean the other is spotted it looks like mud and it is this is soil on the glove soil splashed up by the rain you've seen places where rain has splashed and washed away soil and you must have noticed that there are no plants in these places plants help to hold soil together and keep it from being washed away what's one reason why there are no plants here and no plants here there are many plants here and we know one of the reasons for this soil we've seen that soil is usually a mixture in it are sand and clay which are bits of rock and humus which is the bodies of many dead plants and some small animals this is soil [Music]