Life In A Cubic Foot Of Soil (1963)

[Music] there are living things all about us living things in the air and living things in the soil are grass and shrubs the only living things in soil as part of a science project these boys and their teacher are going to study a cubic foot of soil they have dug up and placed in a plastic container in a profile of this cubic foot of soil we can see a layer of subsoil and a layer of top soil growing out of the top soil are grasses and other plants this is called plant cover by carefully examining the layers of top soil and subsoil we can find living animals such as this white grub the larvae of a June beetle we can also find other animals that inhabit the soil communities of ants and larger animals earthworms are among the animals seemingly best adapted for living in soil how do living things depend on soil what are some of the relationships between soil and plants and animals to find answers to these questions the boys and their teacher will examine the cubic foot of soil more closely now in the school science laboratory we're ready to look for relationships between living things and soil first we'll have to investigate soil more closely let's start with the subsoil layer what can we notice about its makeup we see that it is composed mostly of clay and larger particles such as Pebbles magnification with a hand lens gives a closer view of the clay and the bits of rock that make up the non-organic material in the subsoil this non-organic material may have come from a stream or a br where moving water tends to grind rock into smaller pieces this is called weathering the rock is gradually reduced to coarse sand fine sand and clay these non-organic materials tend to be found in the subsoil non-organic materials may be further broken down by the roots of plants as we know Roots do two important things they hold plants in place but the main function of roots would seem to be to supply water and certain chemical compounds from the soil which the plants use to produce food materials some of these chemical compounds are found in humus a dark colored organic material in Top Soil let's examine humus to see what we can learn about its composition setting the microscope for low magnification we see that humus is made up of bits of decayed plant and animal matter this makes it organic now preparing another slide of a sample of top soil adding some water and using higher magnification we can see bacteria simple plants these are species of nitrogen fixing bacteria that live in soil these nitrogen fixing bacteria change nitrogen into soluble nitrates used by plants these bacteria act on the nitrogen in the air that penetrates the soil other kinds of nitrogen fixing bacteria live in the nodules of the roots of clover and other legumes so Clover and other legumes are especially beneficial to soil increasing its nitrogen content do we have nitrates in our soil sample chemists test for nitrates in humus in the following way some humus and water are mixed together in a test tube then an equal volume of feris sulfate is added now holding the test tube in an inclined position concentrated sulfuric acid is added at the junction of the acid and the other Solutions a brown ring forms this as chemists know indicates that the humus being tested contains a nitrate so we found nitrogen in the soil a chemical converted into nitrates and used by plants now we would like to find whether there is evidence of other living things in the soil several days ago these boys placed some moist humus in a patry dish here's what grew on the surface a mold if we investigate a sample of this simple plant under a microscope what can we see we notice that the mold is made up of a mass of threadlike stems called hyy the growing hyy of many moldes enter the organic matter in the soil and help break it down the penicilium mold is sometimes found in soil too it is the source of a very useful antibiotic penicillin are the moles and bacteria we have seen the only forms of microscopic life found in soil the sample of damp soil was taken from the edge of a pond and kept moist let's examine some of it the wet soil sample is put on another slide here we see a species of blue green algae like bacteria and molds algae also contribute to the organic content of soil in addition to algae certain species of one celled animals the protozoa also inhabit moist soil this is ugina one kind of protozoa found in moist soil the protoo we have seen are among some of the animals found in soil remember this grub we saw earlier it is the larval stage of the June beetle sometimes when we examine soil we may find an empty pupil case this pupil case was left when the June beetle grub or larvae emerged into its adult stage and flew away certain stages of the life cycles of many insects are spent in soil by digging further into a section of soil and carefully spreading it out for observation the boy has found ant larvey and ant pupy grasshopper eggs and the Cocoon of an earthworm when earthworms hatch they become useful organisms in soil look carefully at this earthworm burrowing in our sample of soil burrowing help air circulate in soil these little Mounds on the surface of the soil are earthworm casts or wastes which also enrich the top soil with the hand lenss we may discover smaller animals in our cubic foot of soil here we see a ladybird beetle here on the left is the pupa and on the right the larvae of a meal worm let's summarize what we've learned about our cubic foot of soil animal and plant matter Decay and become part of the soil as humus we've noted that humus is a material containing nitrates chemical compounds essential for plant life we've also noted how plants and animals contribute to the building of soil in the soil itself we found and identified a number of different plants and animals we found that our cubic foot of soil contained bacteria molds and algae along with larger green plants such as grasses and clover examples of animal life included insects worms protozoa both animals and plants living and dead contribute greatly to the fertility of soil and the soil in turn provides a basis for the growth of other living things the plants and animals that help make possible human life on Earth