School Science Lessons
Soils
Updated: 2008-07-19
Please send comments to: J.Elfick@uq.edu.au
See also: Interesting websites

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Table of Contents
6.1.0 Study soils
6.2.0 Soil nutrients, fertilizers
6.3.0 Soil particles
6.4.0 Soil profiles
6.5.0 Soil air
6.6.0 Soil water
6.7.0 Soil acidity
6.8.0 Soil conservation
6.9.0 Soil minerals
6.10.0 Soil life
6.11.0 Coral soils
6.12.0 Geology

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6.1.0 Study soils
6.01 Why study soils
6.02 Plants need soil
6.1 Types of soils
6.2 Soil forms from rocks by heating
6.3 Soil forms from rocks by mechanical action
6.25 Angles between mud cracks
1.33 Plants need soil (primary)
1.37 Soil with a magnifier (primary)
2.37 Collect soils (primary)
3.35 Soil contents (primary)
5.39 Make clay pots (primary)

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6.2.0 Soil nutrients, fertilizers
6.4 Fertility of different soils
6.5 Nutrition from the soil
6.9 Compare fertility of subsoil and topsoil
6.37 Fertilizing the soil
5.18 Fertilizing the soil
6.33 Fertilizing soil (primary)
6.38 Plant foods
6.39 Plants need nitrogen, nitrogen cycle
6.40 Legumes
6.41 Make compost
6.42 Artificial fertilizers
6.44 Nutrient cycles
6.46 Crop rotation
5.23 Crop rotation
19.1.20.6 Test for nitrate / nitrite with dipsticks
5.25 Plant nutrients from plant ash
6.9.6 Preparing ground
6.9.7 Improving soil
6.9.13 Mulching the soil
6.9.15 Fertilizing the soil
6.9.17.0 Chemical fertilizers
6.9.14.0 Composting
6.9.14.1 Humus
6.9.14.2 Organic materials for composting
6.9.14.3 Carbon / nitrogen ratio
6.9.14.4 The 3 methods of composting
6.9.14.5 Compost inspection
6.9.14.6 Starting composting for the school garden
6.65.8.1 Natural fertilizers (primary)
9.11.3.1 Natural fertilizers
6.65.8.2 Mulch garden soil (primary)
6.65.8.3 Cover crops and green manures (primary)
6.65.8.4 Fertilizer trial (primary)
6.34 Chemical fertilizersl (primary)
6.31 Describe soils (primary)
6.32 Test soil texture (primary)
6.33 Fertilizing soil (primary)
6.34 Chemical fertilizers (primary)
5.38 Mulch garden soil (primary)
5.35 Fertilizer triall (primary)
5.36 Cover cropsl (primary)

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6.3.0 Soil particles
6.6 Particle sizes of soils
6.6.1 Measure soil texture by hand
6.6.2 Measure soil texture with a texture triangle
6.29 Wind deposits
1.34 Good soil and bad soil (primary)
1.35 Feel good soil (primary)
2.38 Shake soil in water (primary)
6.32 Test soil texture (primary)

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6.4.0 Soil profiles
6.26 Soil horizons of a soil profile
6.30 Soil profiles
6.31 Soils change with depth
5.34 Soil profiles (primary)

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6.5.0 Soil air
6.8 Soils contain air
2.40 Air in soil (primary)
3.34 Soil air (primary)

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6.6.0 Soil water
6.10 Soils contain water
6.11 Water content of soils
6.13 Water rises in soils
6.14 Water-holding capacity of soils
6.32 Water from leaves
6.33 Soil water
6.34 Water through soil
6.35 Water rises up soil
6.36 Mulch saves water
3.33 Soil water (primary)
6.49.3 Soil water (primary)
6.49.5 Soil water bottle (primary)
4.37 Soil water bottle (primary)
6.19 Soil permeability
6.21 Capillary action in soil and deposition by groundwater
6.22 Infiltration and capillary action by groundwater
4.36 Water climbs up soil (primary)
3.36 Waterlogged soil (primary)
2.39 Water through soil (primary)

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6.7.0 Soil acidity
5.19 Acid soils and alkaline soils
6.12 Test soil pH, acid soils and alkaline soils
6.12.1 Use of a commercial soil pH test kit
6.12.2 Preferred pH ranges
6.12.3 Change the pH of potting mix
6.12.4 Raise soil pH with agricultural lime / dolomite
6.12.5 Lower soil pH with agricultural sulfur

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6.8.0 Soil conservation
6.15 Running water changes soils
6.16 Raindrops affect soils
6.17 Splash sticks
6.18 Soil erosion
6.27 Plants can prevent soil erosion
1.36 Protect topsoill (primary)
4.34 Protect soilsl (primary)
4.35 Natural fertilizersl (primary)
5.37 Rain on slopesl (primary)
6.30 Protect our soils (primary)
6.31 Describe soils (primary)
6.62.1 Protect our soils (primary)
6.62.3 Protect topsoil (primary)

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6.9.0 Soil minerals
6.43 Chalk (lime) content of the soil
6.20 Soil salts, soil minerals in solution
6.23 Oxidation of iron
6.24 Freezing water expands
6.45 Soil-less culture (hydroponics)
6.9.18 Soil-less culture (hydroponics), Knop's solution
6.9.19 Mineral deficiency experiment
9.11.3.2 Make potash from ash

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6.10.0 Soil life
6.28 Life in the soil
6.63.1 Soil animals
3.32 Soil animals (primary)

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6.11.0 Coral soils
6.47 Water lens in atolls.
6.48 How soils form in atolls
6.49 How atoll soils change
6.29 Protect our coral reefs (primary)

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6.12.0 Geology
35.3.1 Minerals mined at the Broken Hill mines
35.14.2 Opals
35.21.8 Classify igneous rocks in hand specimens
35.40.1 Mapping contours, geological structures, erosion
35.40.2 Isostasy model

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6.01 Why study soils
You study soils because soils give us food. Soils may be not very fertile but you can improve them if you know how to do it.
Many plants will not grow well in coral soils, e.g. bananas will not grow in coral sand under the coconuts because coral soils are poor soils.
Soils are not all the same so you should go outside to look at the soil surface in different places.
The differences may include the following:
Colour: [white, grey, black, reddish]
Particles: [sand only, stones only, sand and stones, fine sand, mud]
Grass cover: [thick cover, few grasses, none]
Other plants: [few, none, many, names of plants]
Dead leaves: [many, a few, none]
Nearby coconuts: [many, few, none]
Go outside to look at the soil surface at six different places and record their appearance.

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6.02 Plants need soil
Plants need soil for the following reasons:
1. Soil holds up the plants. It supports them and holds them firmly.
2. Soil holds water for the plants. Plants need water to grow.
3. Soil holds foods for the plants. Plants must have these plant foods or they cannot grow.

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6.1 Types of soils
Plants need soil to support them and hold them firmly, provide water, provide mineral salts. Obtain samples of soil from as many places as possible and put them in glass jars. Try to get samples of soil from swamps, hill sides, woods, meadows, dunes, river flats, and other localities. In this way you will gather sandy, loamy, and clay soils with a range of colours and decayed matter or humus contents. Study the samples and examine particles from each sample with a magnifying glass. Note the colour, particle sizes, grass cover, other plants, aggregation of soil particles into lumps and the hardness of the lumps, inclusions of stones.

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6.2 Soil forms from rocks by heating and mechanical action
Heat rocks then pour cold water on them. The rocks often break up both when being heated and when being rapidly cooled. Roots can penetrate between layers of rooks and push them apart. Find some soft rocks such as shale or weathered limestone in your locality. Crush and grind them into small particles.

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6.3 Soil forms from rocks by acvids produced by plant roos and decaying pant material, humus.
Find soils with a deep layer ofhumus and test the pH.

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6.4 Fertility of different soils
Obtain samples of soils from a flower or vegetable garden, from a wood, from a place where foundations are being dug, from a sandy place, from a clay bank. Place the samples in separate flowerpots or glass jars. Plant seeds in each type of soil and give each plant the same amount of water. Note the type of soil in that the seeds sprout first. After the plants have started to grow, note the soil sample in that they grow best. Record rates of growth of plants in different soils.

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6.5 Nutrition from the soil
1. The rate of plant growth reflects the ability of plants to extract nutrients from rocks. Grind samples of quartzite, schist, basalt, limestone. Plant radish seeds in each sample and note rates of plant growth.
2. Good agricultural soils have low levels of "exchangeable" sodium. With high exchangeable sodium, aggregates break down to form a dispersed layer causing water-logging and later particles dry to form hard clay. Use swelling clay from a dry clay pan, e.g. montmorillonite. Pack clay into 2 tubes. Add sodium chloride to one tube and calcium chloride to the other tube. Pass water through both tubes and note the different rates of water passing.
3. Put a layer of cotton wool in five Petri dishes. Add (a) 50 mL of normal nutrient solution (b) 50 mL of nutrient solution without nitrogen (c) 50 mL of nutrient solution without potassium (d) 50 mL nutrient solution without iron (e) 50 mL of deionized water. Put 10 small same size plants on the cotton wool in each dish. Put the dishes in an empty fish tank with a glass top to form a moist chamber. Look at the growth of the plants every two days. After two weeks there is an obvious difference in the growth of the plants in the various dishes. The plants in (a) are thriving best of all, while the plants in (e) are the worst. The plants in (b) are almost as badly developed as those in (e). The plants in (c) are better developed. The plants in (d) are as large as the plants in (c) but are yellow-green, chlorotic.
4. Collect white ash from burnt wood. The black ash is carbon. Show the white ash you have collected. Let students taste it. The taste is salty. The ash contains plant nutrients. Show a bag of fertilizer let them read the names written on the bag. Do not let the students taste the fertilizer from the bags. Plant nutrients are chemicals that plants take in from the soil. Some people call them plant foods. These chemicals are needed by the plant to keep it alive, to make food, and make the plant body. If there are not enough plant nutrients in the soil, the plant will be weak, grow slowly, and have yellow or brown leaves. It may die.
The most important plant nutrients are: nitrogen - for plenty of strong green leaves, phosphorus - for root growth and making fruit, potash (potassium oxide) - for healthy plants, potash (potassium oxide) - for healthy plants. Other important plant nutrients are: sulfur and iron for green leaves, magnesium and calcium - for healthy plants. There are other plant nutrients needed in very small amounts, which may be important for some plants, e.g. manganese, boron. Most plant nutrients originally come from the rocks that formed the soil. Other plant nutrients in the soil have come from plants that have died then rotted in the soil. If a soil does not have enough of any plant nutrient, e.g. potash, you say it is deficient in potash.
5. Composition of mature maize plant dry matter: Oxygen 46.43%; Carbon 43.57%; Hydrogen 6.24%; Nitrogen 1.46%; Phosphorus 0.20%; Potassium 0.92%; Calcium 0.23%; Magnesium 0.18%; sulfur 0.17%; Iron 0.08%; Silicon 1.172; Aluminium 0.11%; Chlorine 0.14%; Manganese 0.04%; Trace elements 0.093%
Ten elements are essential for the growth of a green plant. Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Sulfur (S), Phosphorus, Potassium (K), Calcium (Ca), Magnesium (Mg). and Iron (Fe). Plants take in carbon dioxide from the air and hydrogen and oxygen from the water in the soil. Plants absorb other elements with the soil water as salts.

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6.6 Particle sizes of soils
1. The size of soil particles, and their respective ratio is important in the economic management and productivity of soil. Fill a 100 mL graduated cylinder to the 30 mL mark with the finely divided soil sample, with stones and plant debris already removed. Add water to the 100 mL mark. Close the graduated cylinder with a rubber stopper. Shake vigorously several times until the whole of the soil sample is suspended. Allow the graduated cylinder to stand while the soil particles settle. The soil particles settle out according to their rate of sedimentation, in the following sequence, from the bottom to the top: coarse sand 2.0 mm to 0.2 mm, fine sand 0.2 mm to 0.02 mm, silt or dust 0.02 mm to 0.002 mm, clay < 0.002 mm. The clay particle may remain in suspension for a long time. Examine a small sample from each layer with a magnifying glass.
2. Obtain a glass jar that holds about 2 litres. Place several handfuls of soil in the jar. Fill the jar with water, and then thoroughly shake up the soil in the water. Let the jar stand for several hours. The size, shape and density of soil particles determine the order in which they will settle. The largest, more angular, and densest particles will settle out first, and will be on the bottom. The layers in the jar after settling will show decreasing size, angularity, and density from bottom to top. Examine a small sample from each of the layers with a magnifying glass.

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6.6.1 Measure soil texture by hand
Texture refers to the feel of the soil. It is based on the varying amounts of sand, silt and clay in the soil. To estimate the texture of a soil: take a handful of soil and moisten it with water, a little at a time nead the soil and continue to moisten it until you have a ball of soil which is moist all the way through now use the following key to estimate the texture of the soil.
Step 1.
The soil will not roll into a ribbon, go to Step 2.
The soil will roll out into a ribbon about 8 cm long and 0.5 cm thick but it cannot be turned into a ring without cracking, go to Step 4.
The soil rolls easily into a ribbon and can be turned into a ring. No sand can be felt, go to Step 7.
Step 2.
The soil feels gritty, go to Step 3.
The soil feels silky, the soil is a silty loam.
The soil feels neither gritty nor silky, the soil is a loam.
Step 3.
The soil will make a firm ball, the soil is a sandy loam.
The soil does not make a firm ball but colours your fingers, the soil is a loamy sand.
The soil neither makes a firm ball nor colours your fingers, the soil is a sand.
Step 4.
The soil feels gritty, go to Step 5.
The soil feels silky, go to Step 6.
The soil feels neither gritty nor silky, the soil is a clay loam.
Step 5.
The soil feels like gritty plasticine to mould, the soil is a sandy clay.
The soil feels earthy, the soil is a sandy clay loam.
Step 6.
The soil feels like plasticine to mould, the soil is a silty clay.
The soil feels silky but more earthy, the soil is a silty clay loam.
Step 7.
The soil is easy to mould, the soil is a light clay.
The soil is fairly stiff to mould, the soil is a medium clay.
The soil is very stiff to mould, the soil is a heavy clay.

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6.6.2 Measure soil texture with a texture triangle
See diagram 6.6.2a: Soil texture triangle | See diagram 6.6.2b: Using the soil texture triangle
See the map of soil textures on the soil texture triangle
If the percentage of sand, silty and clay is known, use a soil texture triangle to describe the texture of the soil.
If a soil; sample contains 35% sand, 25% silt and 40% clay
Find the position of 40 % clay on the left side of the triangle and draw a line parallel to the base of the triangle.
Find the position of 25 % silt on the right side of the triangle and draw a line parallel to the left side of the triangle.
Find the position of 35 % sand on the base side of the triangle and draw a line parallel to the right side of the triangle.
The intersection of the three lines on the map of the soil texture triangle shows that textual class is a clay.
Similarly, if a soil; sample contains 20% sand, 40% silt and 40% clay, the textual class is silty clay.
Also, if a soil; sample contains 60% silt and 30% clay, the % sand is 10% and the textual class is silty loam.

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6.8 Soils contain air
See diagram 6.8: Air in soil
Put soil in a container and slowly add water. Observe the air bubbles that rise through the water from the soil.

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6.9 Compare fertility of subsoil and topsoil
Obtain a sample of good topsoil from a garden. Obtain another sample of soil from a depth of about 50 cm. Place the samples in separate flowerpots and plant seeds in each. Keep the amount of water, the temperature, and the light equal for each sample. Note that soil produces the healthier plants.

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6.10 Soils contain water
See diagram 6.10: Water from dry soil
Put soil on a piece of tin or in an evaporating dish and heat it slowly. Cover the soil with a glass cup or filter funnel and note water condensing on the cool sides.

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6.11 Water content of soils
Collect samples of soil in metal drink-cans. Weigh the drink-cans and adjust the soil content so that the weight of each drink-can and soil is the same. Heat the drink-cans and soil in an oven at 105^oC until all the soil is dry. Calculate the water content of each soil sample. Compare soil samples sheltered from rainfall with unsheltered soil samples. Compare the absorption of these samples with daily rain gauge data. For example, compare how 25 mm of rainfall affect the absorption of exposed soil, contrasted with an unexposed control sample.

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6.12 Test soil pH, acid soils and alkaline soils
Acid soils and alkaline soils
This topic is very important because you can improve the fertility of your garden soils by treating them so that they are not too acid or too alkaline. The pH scale measures whether substances are acid or alkaline.
pH 1 very strong acid that can burn you, e.g. battery acid
pH 6 weakly acid, e.g. soda water
pH 7 neutral, neither acid nor alkaline, e.g. water
pH 8 weakly alkaline, e.g. soap
pH 14 very strong alkali that can also burn you.
Acids have a sharp raw taste, e.g. unripe oranges or bush limes.
Alkalis have a slippery feel, e.g. soap, saliva.
Plants can absorb plant nutrients best when pH is 6 to 7. In soils formed from coral rock the pH will be too high. In swampy land the pH will be too low. To lower the pH add rotten compost. To raise the pH add lime.
1. Take soil samples with a teaspoon. Add an equal amount of water to each sample, enough to cover the soil. Shake the samples thoroughly then drain off the liquid or use a filter. Test the pH of the collected liquid.
2. Use a commercial pH testing kit. Put a level teaspoon of soil on a white tile. Add 5 drops of pH due indicator liquid and stir with the rod provided. Dust the paste with the white powder, barium sulfate. Wait for one minute. Read from the colour card the pH value of the colour nearest to that of the sample.
3. Most soils are either slightly acid or slightly alkaline. Acid soils have pH values of less than 7. Alkaline soils have pH values of more than 7. Plant growth is affected by soil pH. Few plants grow well in soils with pH values below 5.5. Most other plants grow best in soils with pH values 6 to 7.
4. Plants adapted to acid soils may not get enough iron and manganese from alkaline soils. Their young leaves show yellowing, chlorosis, and growth is poor. Severe deficiency leads to death. Plants adapted to alkaline and slightly acid soils can be harmed by dissolved aluminium and manganese in very acid soils and may not get enough calcium. You can raise soil pH by adding agricultural lime or dolomite.
6. Check the pH of mix in pots because most fertilizers produce acidity. Raise pH with a suspension of 5 g of hydrated lime (builders' lime) in a litre of water. Lower pH with 2 g of iron sulfate in a litre of water. Within two minutes heavily water the pot to remove excess salt.

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6.12.1 Use of a commercial soil pH test kit
1. The test kit contains one bottle of pH dye indicator and one bottle of barium sulfate solution. Place a level teaspoon of mixed soil or potting mix on the test plate. Add 3 to 5 drops of indicator liquid and stir with the rod provided. Dust the paste with the white powder provided. Wait one minute. Read from the colour card the pH value of the colour nearest to that of the sample. For a garden bed, take at least five samples from holes dug in different parts of the bed. Each sample is to extend from the surface to a depth of 10 cm. Test each sample separately. For farm paddocks, take at least 20 samples from each area. Mix samples together thoroughly and test as one sample. For bought and home made potting mix, thoroughly mix the bulk lot. For mix in a pot, first knock the root ball from the pot. Remove a wedge of mix representing the whole depth of the root ball. Mix thoroughly. For a mix in large tubs, dig down the side of the root ball as deeply as is possible. Thoroughly mix the sample removed.
2. Show how to use a soil pH test kit
Plants cannot absorb plant nutrients from the soil if the soil is too acid or too alkaline. Soils that are not well drained are too acid. Soils made from coral rocks are too alkaline. You can test the soils using a colour test. If the colour of soil in the test turns yellow orange, the soil is too acid. If colour if soil in the test turns blue purple, the soil is too alkaline. If colour if soil in the test turns dark green, the soil is not too acid nor too alkaline. Collect just enough soil from just under the surface of the soil to cover your little finger nail, and place on a white plate. Shake two drops of the indicator on the soil and mix to a paste with the stick. Sprinkle some special white power on the paste. Wait a few minutes then match the colour of the powder with the colour chart. Do this for swampy soil, coral soil, dark well drained soil.
3. Acids have a sharp sour taste and can dissolve substances, e.g. in a car battery.
Alkalis have a slippery feel and can dissolve substances, e.g. soap.
Plants cannot absorb plant nutrients from the soil if the soil is too acid or too alkaline. Soils in swampy ground are too acid for most plants. Soils made from coral sand are too alkaline for most plants.
You can make soil less acid by adding burnt shells hammered to a powder, and by draining the soil. You can make soil less alkaline by adding rotten plants from a compost heap.
Good soil is dark in colour from the rotten plants and is well drained. To make sure that the soil is not too acid and not too alkaline the agriculture field officer can do a soil test.

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6.12.2 Preferred pH ranges
1. For the best growth of plants it is essential that the acidity (measured by pH) of the potting mix or soil is suitable for the plants you want to grow. Most soils are either slightly acid or slightly alkaline. A few are neutral (between acid and alkaline). Some soils are very acid and some are very alkaline. Neutral soils have a pH of 7. Acid soils have pH values of less than 7; alkaline soils have pH values of more than 7. Plant growth is affected by soil pH. Few plants grow well in soils with pH values below 6.5. Plants whose native habitats had very acid soils grow best in soils of pH 6.5 to about 6. Most do not grow well on neutral and alkaline soils. Most other plants grow best in soils whose pH values are about 6 to 7. Plants whose native habitats had alkaline soils will grow on slightly acid soils, but they will also grow well on alkaline soils. Most plants grow well in potting mixes when the pH of the mix is in the range 5.5 to 6.5. Plants from areas with very acid soils prefer a potting mix with a pH in the range 6.5 to 5.5. Plants adapted to acid soils are often unable to get enough of the essential nutrients iron and manganese from alkaline soils. Their young leaves show yellowing (chlorosis) and growth is poor. Severe deficiency leads to death. By contrast, plants adapted to alkaline and slightly acid soils can be harmed by the amounts of dissolved aluminium and manganese present in very acid soils. They probably cannot take up enough of the essential element calcium.
1.1 Soils of pH 6.5 to 6; potting mixes of pH 6.5 to 5.5
Camellia, Rhododendrons, Azalea, Gardenia, Erica, Macadamia, Juniper, Spruce, Japanese Maple
1.2 Soils of pH 5.8 to 7.5; potting mixes of pH 5.3 to 6.5
Most vegetables, bedding plants, commonly grown shrubs and trees.
1.3 Soils of pH 7 and higher; potting mixes of pH 6 to 6.7
Many cacti and succulents. Plants native to arid areas.
Grow roses and citrus that have been grafted onto rootstocks that tolerate these soils.

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6.12.3 Change the pH of potting mix
The mix must be moist enough to use for potting. Raise pH with dolomite. Add 1 to 1.5 g/L of mix to raise pH by about one unit.
Lower pH with sulfur. Add 0.3 g/L to lower pH by about one unit. Check the pH again after two weeks storage and add more as needed. Check the pH of mix in pots every few months, because most fertilizers produce acidity. Raise pH with a suspension of hydrated lime (builders' lime). Suspend 5 g (a heaped teaspoon) in a litre of water. Pour the suspension onto the mix in the pot. Use 200 mL for each litre of the mix. (A 130 mm pot contains about 1 litre of mix.) You should pot plants again if the pH of the mix is below 6.5. Lower pH with a solution containing 2 g of iron sulfate per litre of water. Apply 200 mL per litre of mix and within two minutes heavily water the pot to remove excess salt. Wait for one week, check mix pH and add more iron sulfate if needed.

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6.12.4 Raise soil pH with agricultural lime / dolomite
Raise soil pH by adding agricultural lime or dolomite. A 1:1 mixture of the two often gives best results.

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6.12.5 Lower soil pH with agricultural sulfur
Lower soil pH of slightly alkaline soils (pH below 7.5) with agricultural sulfur. The large amounts of solid lime often present in alkaline soils with pH values higher than about 7.5 make it almost impossible to make these soils acid.

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6.13 Water rises in soils
Water moves up in three ways: (a) The roots of plants take water from the soil. (b) The hot Sun evaporates water out of the soil near the surface. It goes away as water vapour. (c). Water can rise in the soil by capillarity, a phenomenon linked to surface tension that causes liquids to rise up fine tubes, capillary tubes, and be absorbed by the spaces in absorbent paper. Soil does not contain capillary tubes but the spaces within soils have large enough relative surface areas for capillarity to occur.
1. Dip the end of a piece of chalk into coloured water. The water rises up the chalk because it has many very small holes. Repeat the observation with dry newspaper or cloth. Dip the end in water and the water slowly rises up the paper or cloth. A wick of a candle works in this way.
2. Cut off the ends of plastic drink bottles to make cylinders. Attach cloth over the bottom ends of the cylinders and fasten the cloth with wire. Put 15 cm depths of soil in the cylinders, e.g. sand, loam, gravel, clay. Stand the cylinders in a pan containing 3 cm depth of water. Note the rise of water in the soil because of capillarity.

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6.14 Water-holding capacity of soils
1. After rain, soil contains much water but usually most of the water goes straight down through the soil and into the water table. To show that water goes through the soil, make a funnel by bending some cardboard round and pin the sides together. Fill the funnel with soil. Pour water onto the top and see how much water goes straight through the soil.
2. Cut off the ends of plastic drink bottles to make cylinders. Attach cloth over the bottom ends of the cylinders and fasten the cloth with wire. Use a curved trowel to dig out cylinders of soil with diameters equal to the internal diameters of the drink bottles. The aim of this procedure is to reduce any change in the natural compaction of the soil sample. Put equal volume soil samples in the cylinders. Under each cylinder, place a dish to hold surplus water. Pour measured volumes of water into each cylinder until the water begins to run through the cloth at the bottom. Note the water-holding capacities of different soils.

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6.15 Running water changes soils
See diagram: 6.15: Water running through tilted trays
1. After a heavy rainfall, take samples of running muddy water. Leave the samples to stand for several hours then observe the settled sediment.
2. Fill a tray with loose soil and fill another tray with firmly packed soil. Tilt both trays to the same angle. Place two containers to collect runoff water. Use a watering can to sprinkle the same volume of water on each tray. Observe which soil is carried down faster and measure the runoff water.
3. Fill both trays with soil, but cover one tray with grass sod from a grass farm. Water equally as before and observe both the erosion and the runoff water.
5. Fill both trays with soil but give one tray more slope than the other. Water equally as before and observe both the erosion and the runoff water.

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6.16 Raindrops affect soils
Clip a sheet of white paper to a board and lay it flat on the floor. Use a medicine dropper to let drops of coloured water fall on the white paper. Note the size and shape of the splashes. Repeat the experiment with the white paper at different angles to the horizontal. Repeat the experiment with the medicine dropper at different heights. Keep the sheets of paper as a record of the different "raindrops".

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6.17 Splash sticks
See diagram 6.7: Splash stick
Paint metre sticks white on one side to show mud splashes. Push the white sticks vertically down into the soil. Use the same force of water from a hose to make mud splashes on the splash sticks. After a rainstorm, note the height to that mud has been splashed on each splash stick.

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6.18 Soil erosion
1. Visit a locality where running water has caused damage by cutting gullies. Note the damage and examine any ways to prevent it.
2. Fill two trays with loose soil, and tilt both trays to the same angle. Make furrows with a stick (a) running up and down the hill in one tray, and (b) running across the hill in the other tray. Sprinkle each tray with the same amount of water. Observe the erosion in each case, and the runoff water. In light rainfall furrows across the hill prevent soil erosion and increase soil moisture. In very heavy rainfall, e.g. in tropical areas, furrows across the hill make cause greater loss of soil as water pushed on the walls of the furrows.
3. Fill the trays with loose soil then add water until the water forms gullies. Block the gullies at intervals with small stones. Add water again and observe the effect of blocking the gullies.

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6.19 Soil permeability
Cut off the ends of metal drink-cans to make cylinders. Attach cloth as a fine screen material over the bottom ends of the cylinders and fasten the cloth with wire. Put filter paper inside the drink-can on top of the fine screen material to prevent fine particles of soil from passing through the screen, Collect samples of coarse, medium, and fine soil. Heat the samples in an oven at 105^oC until they are dry. Put equal amounts of the three soils in the drink-cans. Put the three drink-cans on stands so that water can be poured into them and collected underneath. Pour equal volumes of water into each container. Record the time taken for the water to stop filtering through the soil. Record the volumes of water collected under each drink-can. Note that soils are the most permeable and that soils retain the most water.

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6.20 Soil salts, soil minerals in solution
Ask the local water supply service to tell you the total amount of dissolved mineral matter per unit volume in the untreated drinking water.
1. The soil contains salts to be taken up by plants and used as nutrients. Add demineralized water to cover garden soil in a beaker. Stir the soil and allow any suspended soil to settle. Filter off the liquid on top of the soil. Examine a drop of filtrate under a microscope. Leave the drop to dry and examine the residue under the microscope. Look for crystals of salts.
2. Add drops of 5% cent hydrochloric acid to a sample of the filtrate The intensity of the reaction indicates the chalk content of the soil.
3. Add very dilute hydrochloric acid to pieces or limestone and other rocks. Allow to stand until the limestone dissolves. Note the residue of insoluble matter, e.g. quartz.
4. Ask the local water supply service to tell you the total amount of dissolved mineral matter per unit volume in the untreated drinking water.
5. Study the grade formula of artificial fertilizers. If the fertilizer contains 13% nitrogen, 13% phosphorus and 21% potassium, 100 grams of the fertilizer would contain 13 g nitrogen, 13 g phosphorus and 21 g potassium. The grade formula is NPK =13:13:21. Other examples of artificial fertilizers are as follows: muriate of potash (NPK = 0:0:50), superphosphate (NPK = 0:9:0), sulfate of ammonia (NPK = 21:0:0), urea (NPK = 46:0:0).

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6.21 Capillary action in soil and deposition by groundwater
See diagram 6.21: Solution and deposition
Put a 2 cm depth of a mixture of sodium chloride and fine dry sand in a big plastic container. Cover this layer with 5 cm of clean sand with no salt in it. At one end of the container insert a long stem funnel vertically into the sand so that the end of the stem reaches the sand and salt layer. At the other end of the container fix a heat lamp or put only that end in direct sunlight. Pour enough water into the funnel to wet a layer about 2 cm deep along the bottom of the container. Agitate the stem of the funnel to help the water to move down. Turn on the heat lamp or leave that end of the container in the sunlight for 2 hours. Observe through the side of the container so that you can see water moving through the sand. Near the lamp or sunlight, water rises through the sand by capillary action, bringing the salt in solution up with it. The heat causes the water to evaporate, and the salt forms deposits near and at the surface of the sand.

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6.22 Infiltration and capillary action by groundwater
See diagram 6.22: Capillary action through soil
Half fill two glass tubes, 2 cm in diameter and 30 cm long with dry, fine sand. Support the tubes vertically with clamp stands so that the lower end rest in a dish. Pour water into one glass tube. Observe the water moving down through the pore spaces of the sand, then moving into the dish, then starting to move up the other tube by capillary action.

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6.23 Oxidation of iron
1. Put a small piece of steel wool in a container of clean sand and keep it moist. After some days observe any change in the steel wool and any staining of the sand.
2. Put iron powder on a small piece of pyrite in a container and keep it moist. After some weeks, note the development of a white crystalline substance, iron sulfate. Oxidation of iron minerals is generally accompanied by a change of colour to yellow, brown, and red oxides and hydrated oxides. During rusting, metallic ion changes to Fe(OH)₃.xH₂O, that is later oxidized to hydrated iron (III) oxide, Fe₂O₃.xH₂O, brown rust.

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6.24 Freezing water expands
Fill a glass bottle with water and put the top on securely. Wrap the bottle in a cloth, to prevent the shattered glass from falling. Put the bottle into the freezing compartment of a refrigerator. After 24 hours, carefully remove the bottle and examine it. The glass is cracked because the water increased in volume during freezing. Water has a maximum density at 4^oC. When water cools from room temperature to 4^oC, it is contracting in volume. When water is cooled from 4^oC to 0^oC, it is expanding. At 4^oC the density of water is 1000 kg m^-3. At 0^oC the density of water is 999.87 kg m^-3 and the density of ice is 918 kg m^-3. The temperature of maximum density decreases with salinity.

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6.25 Angles between mud cracks
Use trays to collect samples of different types of clay and fine silt. Add just enough water to cover the samples. Put the collection trays in direct sunlight and note how mud cracks form. Compare the number of formed mud cracks from tray to tray. Note the angles formed as the mud cracks appear. The pieces of dried mud have a roughly hexagonal shape.

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6.26 Soil horizons of a soil profile
See diagram 6.26: Soil horizons
Mature soils usually show a well-marked profile consisting of three main layers or horizons designated A, B, and C. These differ in colour, texture, and structure and vary in thickness. The A horizon is called the topsoil. Soluble materials are removed by percolating water. Topsoil is usually rich in organic matter and in soil organisms. The B horizon is called the subsoil. This horizon accumulates clay washed out of the topsoil above. Iron minerals are usually present and most likely they will be oxidized. The C horizon is the unconsolidated, weathered parent material. Make models of soil horizons from various places and compare the depths of the A and B horizons.
1. Dig a hole with a flat spade one metre deep in the soil. Make one side of the hole flat to see the different layers or parts of the soil. Soils may be dark or light at the surface, deep or shallow depth to bed rock, stony or sandy. The roots of plants may go deep or are all near the surface.
2. Examine soil horizons in fresh road cuts or in gullies.
3. Use a flat spade to make a clean vertical cut to expose the horizons. Let the material dry. Smear glue on one side of a board and press the board against the cut soil so that particles from each horizon stick to the board. Compare different soil profiles, noting the depths of the horizons and the composition of the material at each horizon.

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6.27 Plants can prevent soil erosion
1. Observe an area where the soil has eroded because of lack of plant cover. Discuss why the area looks as it does. Show how plants may stop the soil from blowing or washing away.
2. Plant grass seed in a section of sandy soil, in an erosion table. Run water down the erosion table when the grass has developed a network of roots. Note how the roots have a holding effect on the soil. Pull out some sprouting grass, run water on this area and note any new soil erosion.

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6.28 Life in the soil
See diagram 6.28: Berlese funnel
1. Put a soil sample in a very clean glass funnel. Suspend a 100 watt light globe over the funnel. Put a beaker containing methylated spirit under the funnel. Turn on the light. Over the next few days the heat from the light globe will cause living animals to move away from the globe and fall down the funnel into the methylated spirit.
2. Examine the surface of a square metre of soil. Note any earthworm mounds, anthills, or other signs of animal activities. Carefully remove the surface plant life and examine the soil for more signs of animal life. Note how earthworms cause more air to enter the soil through their burrows. Their digestion of soil particles changes the composition of the soil and their droppings and dead bodies change the composition of the soil.
3. Compare the germination and growth of plants in normal soil and soil put in a microwave to kill all living things in it.

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6.29 Wind deposits
Use three large trays filled with moist sand, dry sand, and flour. Place the tins near an electric fan directed to blow towards the tins. Move each tray towards the blowing fan until a slight movement occurs in the pile of material. Note the distance at that each showed movement because of the artificial wind. Observe any pattern in the way the materials have blown. The lightest material is the farthest away and the heaviest is the closest. Note how larger particles are sorted. This sorting mechanism occurs frequently in nature.

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6.30 Soil profiles
See diagram 6.26: Soil profiles
To make a soil profile with a spade, dig a hole 1 metre deep in the soil. Make one side of the hole flat to see the different layers or parts of the soil.
Not all soil profiles are the same. Soils may be dark or light at the surface, deep or shallow (depth to bed rock), stony or sandy. In some soils the roots of plants go deep. In other soils the roots are all near the surface.
1. Dig profiles in different places then record what you see.
2. Dig down until the soil profile does not change. The holes should not be more than 1 metre deep. Fill the holes after each lesson.
3. Dig a profile in the most common kind of soil. Record what you see. [The top part of the soil is the darkest. The soil is in layers.]
The dark soil at the top of the profile is the topsoil. This is the richest part of the soil. You see the dark colour where there are rotting plant leaves and roots. The black colour comes from organic carbon compounds left when the leaves and roots rot completely. The lower part of the soil is the subsoil. Below the subsoil is the bed rock or coral reef.
6. Dig other profiles and record what you see. Then fill in the hole.
5. Dig a hole in a place where the topsoil is very dark. Collect samples of black soil near the top of the profile and light sandy soil down near the bottom of the profile. Put these samples into two separate tins with small holes in the bottom of the tins. Sow several different kinds of seeds in both soils. Water each soil. Place tins in a shady place where they will only get morning sun. After the seeds have germinated and grown, which soil made the plants grow best? [The dark topsoil is better than the subsoil for growing plants.]

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6.31 Soils change with depth
See diagram 6.7: Soil auger
1. Make a soil auger from pipe. Turn the auger down into the soil and pull out samples from different places and at different depths. Keep the soil depth samples in plastic boxes. An alternative to using a soil auger is to examine soils exposed in roadside cuttings.
2. Construct a soil auger from a carpenter's wood drill bit. This should be welded to a steel shank about 2 cm in diameter and about 50 cm in length. A cross member welded to the shank will provide leverage to rotate the auger when it is drilled into the ground. By simply turning the auger down into the soil and pulling it out of the ground at intervals, samples which stick to the bit can be extracted from various depths. A grid for a specific area of the land can be made, and soil depth samples taken and compared to give a picture of subsurface conditions for that area. Afterwards, these individual soil samples can be mounted as models, or the simple observations can be recorded.

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6.32 Water from leaves
See diagram 9.194.1: Water comes out of leaves | See diagram 9.195: Plants lose water
You need a mirror and a tree with leaves that you can push inside a clear plastic bottle or plastic bag. Water is in all parts of the plant - in the stems, leaves, flowers and roots. Also, coconuts have nut water in the fruit. Plants lose water from their leaves. You cannot see this water because it is water vapour but you can show that it is there. You can do simple experiments with water vapour. Take a piece of glass and breathe on it. You cannot see the water in your breath but you can see the water that collects on the glass. Push some live leaves from a growing plant inside a clear plastic bottle or plastic bag. Do not break the leaves off the tree. Close the mouth of the bottle or plastic bag. After 20 minutes go out and look at the bottle or plastic bag. Small drops of water form inside it. This water has come out of the leaves. The movement of water through the plant is called transpiration.

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6.33 Soil water
See diagram 35.6.7: Water from dry soil
Dig down about 15 cm into the soil and take a match box full as a sample. Put some of this soil onto a piece of tin. Cover it with a glass or glass cup. Heat the underside of the tin with a lamp or a candle. Small drops of water will form on the inside the glass showing that water is in the soil.

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6.34 Water moves down through soil
See diagram 35.6.7: Water through soil
Water may not stay in the soil. After rain, soil contains much water. Most of the water goes straight down through the soil and into the water table. To show that water goes through the soil, make a funnel by bending some cardboard round and pin the sides together. Fill the funnel with soil. Pour water onto the top and see how much water goes straight through the soil.

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6.35 Water rises up soil by capillarity
See diagram 35.6.7: Water moves up

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6.36 Mulch saves water
See diagram 6.65.3: Coconut mulch
You can save soil water in two ways:
1. (a) Cut down weeds and bushes that grow near your coconuts, breadfruit, vegetables or bananas. Then the roots of these plants cannot steal the soil water.
1. (b) Cover the surface of the soil around your plants with a layer of dead leaves, grass or other material. This layer is called a mulch. The mulch stops the hot sun from making the soil surface dry.
2. Weeds and bushes take soil water from the coconuts, breadfruit and other useful plants. Cut down but do not burn these weeds because you can use them for mulch.
3. Mulch keeps the soil moist around plants. Mulch is any light, loose covering on the soil. Old dead grass, coconut leaves and breadfruit leaves make good mulch.
6. Some ways to save soil water:
(a) Cut down weeds that steal soil water from trees.
(b) Put a mulch of dead leaves around young trees or vegetables.
(c) Make some mulch. Gather dead leaves or grass and make a mulch around some young tree such as a coconut seedling or a young breadfruit. The next week, lift up the mulch to see that the soil under it is cool and moist.

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6.37 Fertilizing the soil
Note that there are three methods of fertilizing the soil but the word "fertilizer" usually refers to artificial fertilizer. Examine a bag of fertilizer, e.g. Muriate of Potash that contains potash or sulfate of Potash, which contains potash and sulfur. "Potash" is an old name for potassium oxide. Collect same well rotted compost in a jar. Examine the well-rotted compost in a glass jar and the fertilizer bag. Read the words on the bag. There are three ways in which a deficiency of plant nutrients can happen: (a) There is a natural deficiency because there was not much of the plant nutrient in the original rock from which the soil was made, e.g. soils made from coral rock are deficient in many plant nutrients. (b) The plant nutrients have been taken out of the soil by crops. When a crop is harvested, some plant nutrients are lost. (c) The plant nutrients have been washed out by water. There are two ways of increasing plant nutrients in the soil: (a) Stop farming the land for some time. Then plant nutrients will slowly be added to the soil from soil particles and rotten plants. This is called fallow. (b) Add fertilizer to the soil.
There are four methods of fertilizing: (a) Dig compost into the soil. Compost is made from plants, manure, and food scraps kept in a heap and allowed to go rotten before being put in the soil. (b) Grow green manure. Legume crops such as cowpea have little white lumps on their roots that add nitrogen to the soil. If you dig a legume crop into the ground, it is called green manure. (c) Add liquid manure. Fresh (or fowl) manure can damage young vegetables. Put the manure in a 44 gallon drum and cover with water. After one week, use this manure water on the plants. (d) Add Artificial fertilizer such as muriate of potash contains potash. sulfate of potash contains potash and sulfur. These fertilizers are made in factories. Other artificial fertilizers are superphosphate that contains phosphorus and urea that contains nitrogen.

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6.38 Plant foods
Plants need two kinds of plant foods: (a) Main plant foods called nitrogen, phosphorus and potash. (b) Minor plant foods and trace elements. The word "trace" means a very little. One of these traces is Iron and you know that people sometimes bury pieces of old iron under coconut trees. When plants gather plant foods from the soil, they take these foods into their own bodies the roots, stems, leaves and flowers. Most of the plant foods are stored in the plants above the soil. Even when a plant dies or a leaf falls off, the plant foods are still there. Some plant foods are in the soil and some are stored in the stems and leaves of plants. Some plant foods are lost when people harvest and eat the plants. These plant foods leave their bodies in the toilet. Some plant foods are lost when plant leaves and stems are burnt. Some plant foods are lost when animals eat them, e.g. Pigs kept in pens or houses. You can return plant foods to the soil in these ways: (a) Dig dead leaves and stems of plants into the soil. (b) Burn plants and put the ash in the soil. (c) Collect manure from chickens and pigs to make compost for growing plants.

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6.39 Plants need nitrogen, nitrogen cycle
See diagram 6.65.1: Cycle of nutrients
Nitrogen is the most important plant food. All animals and plants need nitrogen. Plants and animals will not grow well if they do not have enough nitrogen. Nitrogen gas in the air, but most plants and animals cannot use it. Nitrogen occurs in fish, animals like chickens and pigs, animal wastes, plants called legumes and nitrogen fertilizers, e.g. urea. Some foods, e.g. bananas, papaya (pawpaw) and breadfruit, contain very little nitrogen. Students do not grow fast if their parents give them only these foods and boiled white rice but not much fish or meat. Legumes are the pea and bean plants. Legumes are different from other plants because they have small lumps on their roots called nodules. The nodules can catch the nitrogen gas from the air in the soil and use it to build their bodies. So the bodies of legume plants contain much nitrogen. Nitrogen is lost when heavy rain falls on the soil. However, rain will not wash away the nitrogen if it has much humus in the soil to hold the nitrogen. When leaves and plants burn, some nitrogen goes back in to the air as a gas. Nitrogen is added to the soil when people use compost for their plants, when legumes grow in the soil or when leaves and stalks of legumes are used to make compost, and when people add animal manure to the soil.
Nitrogen is lost when: heavy rain washes it out of the soil, plants are burned by fire, animal manure and urine do not go back to the soil.
Nitrogen can be added to the soil when: you put compost on their plants, you grow legumes in the soil or use them to make compost, you put animal manure around plants or use it to make compost.
You can keep nitrogen instead of losing it. Nitrogen can go from the soil to plants, to animals and then back to the soil again.

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6.40 Legumes
See diagram 9.72: Root nodules | See diagram 9.72.1: Legume plants | See diagram 9.72.2: Legume flower | See diagram 9.209: T. S. Root nodule
Legumes used for food are commonly called peas and beans. A bacterium (plural bacteria) called Rhizobium can get into the roots of legumes. Here they cause lumps called root nodules where they live. The bacteria can take the nitrogen gas from the air and put it into their bodies. Rhizobium can "fix" nitrogen from the air. Very few other living thing can fix nitrogen. Some of this nitrogen goes into the stems and leaves of the legume plant. When the leaves fall off, some nitrogen is added to the soil. Other plants can then use the nitrogen to make them grow better. When the legume plants die, the nitrogen fixed by the Rhizobium can still be available to growing plants. If you cut legumes and put them into compost it will be very much better. To make good compost you must add something that contains much nitrogen. Legumes are very good to feed to animals because legumes contain much nitrogen.

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6.41 Make compost
Before teaching this lesson, ask a field officer from the Ministry of Agriculture about compost heaps. In some places the Department of Agriculture does not approve compost heaps because they can be home for insect pests. Prepare to make compost heaps about 2 m X 2 m long and about 1 m high. Many plants do not grow well in coral soils because they are not good soils. The way to make good soil is to put much organic matter into it. Organic matter is anything that contains plant or animal material that was once living, e.g. dead leaves and animal manure. When you put organic matter into the soil bacteria turn them into dark humus, another kind of organic matter. The reason that organic matter in the soil is good for plants is that it has two functions: (a) It holds water very well and can give this to plants. (b) It holds plant foods very well and can give these to plants. To make a compost heap use leaves of different plants, e.g. beach bean (Canavalia), chicken manure, pig manure and fish scraps. You can sprinkle a little nitrogen fertilizer over the compost layers but this is expensive. Build the compost heap by making layers of dead leaves, black soil, and some manure or other nitrogen containing substances. Do this again so you have many thin layers one on top of the other. Then water the compost heap to make it damp. Then cover it with dead coconut leaves to keep the hot sun from making it dry. After five weeks, turn the compost layers over onto another place. Mix up all the layers. Then water it again and cover it with coconut leaves. After another five weeks, do this again. In about three months the compost will be ready to use. If it has been a dry time, it may take a little longer to be ready. You can then mix with some soil - half of each - and use the compost to make a garden bed.

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6.42 Artificial fertilizers
Artificial fertilizers are expensive so you can use them only if your agriculture project has good rainfall and is close to a market. A fertilizer is a substance that is very rich in plant foods. Simple fertilizers contain only one kind of plant food, e.g. if the fertilizer urea contains only nitrogen. Mixed fertilizers contain several plant foods. The three main plant foods are nitrogen, N, phosphorus, P, and potash, K₂O, and are contained in the following simple fertilizers. Urea contains only nitrogen. Ammonium sulfate contains only nitrogen. Superphosphate contains only phosphorus. Sulfate of potash contains only potash. Chloride of potash only potash. Mixed fertilizers are named by numbers. You always use these numbers in the same order: nitrogen, phosphorus, potash, or N, P, K. Thus, 100 kg of the mixed fertilizer 20-14-14 contains 20 kg of nitrogen, 14 kg of phosphorus, 14 kg of potash. Other mixed fertilizers are 9-25-25, 13-13-13 and 13-1-21. Do not put too much fertilizer on the soil, but just sprinkle it on lightly. Do not put fertilizer too close to the plant stem but under the outer leaves. Put some mixed fertilizer on half a vegetable bed to see the effect of the fertilizer.

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6.43 Chalk (lime) content of the soil
The chalk (lime) content of the soil is important for plants. It affects the quality of the soil, e.g. its acidity, heat retention capacity, water balance and aeration. Calcium, an antagonist of potassium, plays a direct role in swelling processes and is also a plant nutrient. The soil contains salts which plants have taken and used as nutrients. 1. Put a small amount of each soil sample on a watch glass. The soil sample may be fresh or air dried and should cover an area on the watch glass 2 -3 cm in diameter. Add 3-5 drops of 5% hydrochloric acid to the soil sample using a pipette. The intensity of the reaction that occurs is an approximate indication of the chalk content of the soil. Take soil samples from as many different places as possible. Compile a table of results.

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6.44 Nutrient cycles
See diagram: 6.0: Nutrient cycle 1 | See diagram 6.0: Nutrient cycle 2
When you harvest a crop you are taking away nutrients from the soil. These nutrients must be replaced if the soil is to remain fertile.
When plant and animal material is being added to the soil (arrow 4 and arrow 8) they contain not only nutrients but also substances such as sugars produced by photosynthesis.
No. 1 The plant roots take in plant nutrients from the soil and rocks.
No. 2 The plant uses the plant nutrients to make it grow and for photosynthesis in the leaves.
No. 3 Some plant nutrients are stored in the sweet potato (kumara) tuber.
No. 4 Dead leaves and stems containing plant nutrients fall to the ground and rot in the soil.
No. 5 The plant nutrients from the rotten leaves and stems can be taken in again by the roots.
No. 6 A pig eats the sweet potato (kumara) tuber and some leaves.
No. 7 Most of the nutrients are used to make the pig grow.
No. 8 Some nutrients leave the pig in the faeces and urine.
No. 9 Nutrients from the faeces and urine can be taken in again by the plant roots.
No. 10 The sweet potato tuber is harvested and taken away or the pig is taken away to be eaten. The nutrients in the sweet potato tuber and in the pig cannot be put back into the soil, they are lost. The lost plant nutrients can be replaced by: (a) fallow. This gives time for more plant nutrients to come from the soil, See arrow No. 1. (b) green manure. This adds nitrogen and other plant nutrients from the body and nodules of legume plants. (c) fertilizing with rotted compost. fertilizing with animal manure. (d) fertilizing with artificial fertilizer.

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6.45 Soil-less culture (hydroponics)
The technology of culture with hydroponics is to use chemical culture solution that includes contain elements essential for plants. It is mainly used in vegetables, flowers and plants and tree seedlings. It is used to beautify the environment and home. You can plant with hydroponics in places, e.g. desert, city roof and balcony. Then you can provide nutrient elements according to what the plant is essential. Water is used in a circle, so it saves fertilizer and water. If houses and classroom use hydroponics culture to plant tomato, cucumber, strawberry, rape, romaine lettuce and ornamental plant etc., it may improve environment and can be eaten. Grow plants in the classroom without soil.

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6.46 Crop rotation
See diagram 5.6.5: Legume root
Collect examples of plants used in crop rotations in the school gardens. Plants can seem different yet be in the same family. Plants from the same family have similar flowers, e.g. legume family, pumpkin family. On way to control plant pests and diseases is to follow a rotation. In a rotation you do not let the same crops follow in the same piece of land.
An example of a crop rotation:
Crop 1 corn (maize) or sorghum (grain crop)
Crop 2 sweet potato (kumara) or cassava or yam or taro (root crop)
Crop 3 Chinese cabbage or lettuce (leafy crop)
Crop 4 Mung bean or snake bean or peanut or cowpea (legume crops), or Crotalaria or Pueraria or Centrosema (legume cover crop)
In the rotation you may have a fallow when you grow no crop, or a green manure fallow when you grow a legume crop and dig it into the soil to rot before the next crop is planted. The legume crop will fertilize the soil when the root nodules and the rest of the plant rots and add plant nutrients such as nitrogen to the soil. Rotations control disease because the same kinds of plants or plants from the same families of plants will have the same pests and diseases. So if you let two different plants from the same family of plants follow in the rotation, the pests and diseases from the first crop will attack the following plants in the next crop.
Some food crops in their families:
Bean family (legumes): mung bean, peanut, snake bean, winged bean, cowpea, Crotalaria, Pueraria, Centrosema
Pumpkin family: pumpkin, melon, cucumber, snake gourd
Tomato family: tomato, egg plant, chilli, tobacco
Taro family: taro, Chinese taro, wild taro
Cabbage family: cabbage, radish, Chinese cabbage
These are two other reasons why a rotation should be followed:
Different kinds of plants take up different kinds of and amounts of plant nutrients from the soil. So a rotation allows a soil to be more fertile.
Different kinds of plants have different kinds of roots. So a rotation helps the soil to keep a good structure.

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6.47 Water lens in atolls
See diagram: Atoll water lens
The water lens deep under the soil contains freshwater. The coral rock of the island is full of small holes. So sea water can go right through the coral rock and sand under the island. However, when it rains, the freshwater pushes the salt water out and makes the water lens. You can dig wells to find this freshwater. The water lens is on the same level as the mid tide level, but is slightly higher in the middle of the island. Freshwater is not as heavy as salt water and it floats on top of it. The lens in thinner near the shores. The lens water rises and falls with the tides. If no rain for some time, the salt water comes into the water lens and makes the lens water salty.

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6.48 How soils form in atolls
See diagram: Forming an atoll 1 | See diagram: Forming an atoll 2 | See diagram: An atoll and its peripheral reef (cross-section)

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6.49 How atoll soils change
When soils change they may become better or worse for plants to live in. Before the lesson, look for examples of soil changes near your school. Also, in this lesson the students record the plants growing in different soils to show that many plants only grow in one kind of place and kind of soil. So plants can indicate the kind of soil under them. Coral soils may change in many ways: (a) The dead leaves of plants fall onto the soil and rot. This gives the topsoil a dark colour. (b) Strong winds may blow sand over the top of the soil and cover it. A new dark topsoil layer may then form over the old layer. Sometimes in a profile you can see the old buried soil. (c) Burning grass will leave black charcoal (carbon) in the soil. You may see layers of charcoal in the soil profile. (d) The light grey stones of floating pumice may be washed onto the island. You may see layers of this rock in a soil profile. This pumice layer can provide some plant foods for coconuts and other plants. (e) Birds may gather in one place and leave their droppings (faeces) there. The droppings contain plant foods and people may collect them for fertilizer (phosphate fertilizer). (f) Humans can change soils too, making them worse, by burning the grass, or making then better, by adding compost. When soils change the plants may also change: (a) Some plants can live in salt spray blown in from the sea, e.g. Pandanus, coconuts, salt bush, but some plants do not like salt spray, e.g. breadfruit.
(b) Some plants can live in a drought, e.g. salt bush, and Pandanus but some plants may die in a drought, e.g. coconuts. (c) Some plants are found on the ocean side and some plants are mostly found on the lagoon side of an island. (d) Go to the ocean side and list plants growing there. Then go to the lagoon side and list plants growing there.

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35.3.1 Minerals mined at the Broken Hill mines
The minerals of Broken Hill are world famous because many of them are rare and beautiful. Unfortunately, most of the rare minerals were found in the top sections of the mine where the sulfide ore minerals had been weathered and oxidized by groundwater to produce a dazzling array of secondary minerals. These areas of the mine are long worked out and not producing ore or mineral specimens anymore.
The main metals mined for at Broken Hill are as follows:
35.3.1.1 Silver, Ag, occurs in a variety of minerals but most of the silver is found as trace amounts of silver mineral locked up inside the lead mineral, galena. Sometimes silver occurs as big lumps, nuggets, of the metal itself. Only silver ever comes out of the ground as a metal. Lead and zinc are always locked away minerals, as is most of the silver. Silver is largely used in the photographic industry although it has uses in jewellery, electronics and silverware.
35.3.1.2 Lead, Pb, occurs mainly as the lead ore galena (lead sulfide, PbS) It is characterized by a metallic silver lustre and cubic fracture. Cerussite (lead carbonate, PbC03) and anglesite (lead sulfate, PbSO4) are found in areas where galena has been weathered or exposed to oxidizing groundwater. Typically this occurred at or near the surface. Lead was used in water pipes, roofing and pigments but is now mostly used in batteries for vehicles and other equipment.
35.3.1.3 Zinc, Zn, occurs mainly as sphalerite (zinc sulfide, ZnS). At Broken Hill it has a black resinous appearance but rarely shows as big crystals. Smithsonite (zinc carbonate, ZnCO3), resulting from the weathering and oxidation of ore by groundwater, is found in areas where the ore body was at or near the surface. Zinc is used in galvanized coatings of iron and steel. It is also used in die cast alloy products, pigments and other industrial and agricultural applications.

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Ore minerals of the primary (sulfide) zone
35.3.2.1 Galena (lead sulfide, PbS is the main lead ore mineral at Broken Hill. The silvery metallic lustre and cubic appearance characterize galena. It has a relative density of 7.35. Galena is also the source of much of the silver at Broken Hill. Silver atoms can substitute for lead atoms or be present within minerals such as acanthite (Ag₂S) that have formed within the galena.
35.3.2.2 Sphalerite (zinc sulfide, ZnS) is the main zinc ore mineral at Broken Hill. Good crystalline sphalerite is unusual at Broken Hill. The colour of sphalerite varies with its impurities. At Broken Hill it is black but some rare large crystals have a deep red colour.

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Gangue (waste) minerals of the primary (sulfide) zone
35.3.3.1 Bustamite, calcium manganese silicate, MnCaSiO6, also occurs in the galena-rich lodes. It has a range of pink to orange to deep brown colours.
35.3.3.2 Rhodonite, manganese silicate ([Mn, Ca]SiO₃) is the most abundant manganese mineral found in the galena-rich ore bodies. It has a range of beautiful red-pink colours.
35.3.3.3 Garnet (spessartine) manganese aluminium silicate (Mn₃Al₂Si₃O₁₂, is a port wine red mineral commonly associated with galena ore.

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Other minerals of the primary (sulfide) zone
35.3.35.1 Chalcopyrite, copper iron sulfide, occurs in veins in garnet, quartzite and garnet sandstone in ore bodies. The associated minerals are argentiferous galena and arsenopyrite.
35.3.35.2 Pyrite, iron sulfide, is found in lining cavities in faults and fractures in ore bodies. The associated minerals are calcite and rhodocrosite.
35.3.35.3 Pyrrhotite, iron sulfide, is found in veins, zones and bands in ore bodies. It can be weakly magnetic but not at Broken Hill. The associated minerals are calcite, galena, and chalcopyrite.
35.3.35.4 Rhodochrosite, manganese carbonate, MnCO₃ is a pink mineral found in fault zones along with other carbonate minerals, e.g. calcite.

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Ore minerals of the oxidized zone
35.3.35.5 Anglesite, lead sulfate, PbSO₄, is another widespread secondary mineral from the oxidized zones of the mine. It is found in vughs (irregular voids) and fractures in all mines in the outcrop area. The associated minerals are marshite, iodargyrite, pyromorphite, stalactitic goethite, and goethite matrix replaced by cerussite.
35.3.35.6 Azurite (copper carbonate) has a habit consisting of short tabular prisms, equidimensional plates, long spear-like crystals with pyramidal terminations. The associated mineral is malachite.
35.3.35.7 Cerussite, lead carbonate, PbCO₃, occurs as ore grade concentrations. It is a secondary mineral from the oxidized zones. Most Broken Hill cerussite is opaque white, but wine yellow, yellow brown. smoky brown, transparent and translucent examples are known. It occurs as reticulated masses, complex arrowheads “twinned crystals”, and "jack straw" masses of tubular-shaped crystals. It is found in ore bodies and is one of the most abundant minerals of the oxidized zone. The associated minerals are malachite, azurite, and bromian chlorargyrite.
35.3.35.8 Copper
Arborescent forms in large cavities, four-sided wire prisms, elongate octahedrons with repeated branches. Also, stalactitic or dendritic masses in wire-like groups and “nail head” crystals. The associated minerals are cuprite and malachite.
35.3.35.9 Coronadite (lead manganese oxide) originally referred to as psilomelane
Massive, stalactitic, shawls, cellular, botryoidal habit. It is abundant in the upper levels of the oxidized zone and outcrop. The associated minerals are goethite that forms the matrix for a variety of secondary minerals.
35.3.35.10 Goethite, FeO(OH), hydrated iron oxide, hydrous iron oxide, has a habit consisting of botryoidal, mamillary, stalactitic masses and crusts. It is abundant in the gossanous capping of the ore bodies. The associated mineral is coronadite.
35.3.35.11 Gypsum, calcium sulfate, has a habit consisting of fibrous, massive, colourless transparent crystals. It is located in ore bodies in the seams, cavities, water courses and crusts in abandoned workings. The associated minerals are rosasite, linarite and dolomite.
35.3.35.12 Malachite, copper carbonate has botryoidal and sometimes velvety habit. It is found in ore bodies as powdery to compact fibrous crusts and hemispherical
aggregates. The associated minerals are azurite and cerussite.
35.3.35.13 Pyromorphite is the most common lead phosphate, Pb₅(PO₄)₃Cl. It is a secondary mineral from the oxidized zone. It has a large range of habits and colours including coatings and sprays, simple hexagonal prisms, stout hexagonal prisms, branching aggregates, mamillated, botryoidal and colloform masses. It is found all along the lode outcrop. The associated minerals are coronadite, cerussite, secondary galena, and anglesite.
35.3.35.14 Silver
Massive, wire habit The associated minerals are gold and copper.
35.3.35.15 Smithsonite, zinc carbonate, ZnCO₃, is a widespread secondary mineral from the oxidized zones. It occurs as rounded botryoidal aggregates resembling drops of wax and as honeycombed masses in ore bodies. It is the most abundant secondary carbonate after cerussite. The associated minerals are coronadite and goethite.

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35.14.2 Opals
See diagram 35.14.1
Opal is similar to chalcedony, but it is a hydrous silica. It has non-metallic lustre, white streak, not good cleavage, conchoidal fracture, white colour, vitreous lustre with colour patches, specific gravity about 2, can scratch glass and be scratched by quartz. This mineral has no definite atomic structure and never occurs as crystals. Opal colour is not formed from impurities or chemicals within the gemstone. Opal has the same chemical structure as glass, SiO₂.nH₂O. However, the molecular structure is different and this difference causes the colour. The opal molecules form in a regular symmetrical pattern. White light enters the opal, and the molecules act as myriads of prisms, and the light is consequently refracted out as various colours. The most famous sources of opal are the Lightning Ridge Opal Mines.
1. Solid light (white) opal occurs as two types, milky and crystal. Milky opal is opaque, with the colours visible on the surface only. Crystal opal is transparent with the colours being visible from within the depths of the stone.
2. Opal triplets consist of thin slices of opal affixed to a background of black glass. A dome of clear quartz crystal is then glued to the upper surface. The opal slice is so thin that it becomes totally transparent. Thus, the black background causes the colours to darken dramatically. The crystal dome is to protect and magnify the opal.
3. Opal doublets are similar in construction to triplets, but without the crystal dome. Thus, a slice of opal is glued to a piece of black glass (or similar substance) and the actual opal is then polished. The opal is generally thicker than a triplet, with better quality opal so doublets are more valuable.
4 Dark (black) opals have dark colours, similar to doublets and triplets. Here, however, the dark background is a natural phenomenon. Thus, a black opal is, in fact, a natural doublet with a band of colour sitting on a dark background. Black opals are very rare, so very valuable.
5. Boulder opals are mined in Queensland, Australia, where ironstone boulders occur with thin veinlets of opal running through them. The stones are cut as natural doublets, with part of the seam of opal as the face, and the ironstone as the natural backing. Boulder opals have a similar appearance to black opals, but have less value.
6. Boulder opal matrix is used when the ironstone / opal amalgam is such that full boulder opals cannot be cut. So the fine veinlets and dark ironstone are polished together.
7. Andamooka matrix consists of a mixture of opal and porous rock, and is white in colour. A regular stone is cut from this amalgam and placed in a sugar solution that soaks into the rock. Sulphuric acid is then applied to carbonize the sugar and turn it black. Thus, the fine slivers of opal now have a black background to give the finished article the appearance of a black opal.
8. Synthetic opals were developed in France several years ago and are virtually never sold in Australia by virtue of the fact that they are synthetic and have little acceptance.
Australia provides the world with 95% of all precious opal. There are eight varieties of opal available in Australia. Before contemplating the purchase of an opal, it is important to understand each type and the principles of their valuation.

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Opal valuation
The three basic criteria of evaluation for all opals, light or dark in colour
1. Colour
The more red visible in an opal, the more valuable. The colour hierarchy is red, orange, green, blue.
2. Brightness
Brightness is most important aspect of opal valuation. The brighter and stronger the colour, the better the quality. Thus a bright green stone can be more valuable than a dull red one.
3. Patterns
The larger the splashes of colour, the better the quality. "Pinfire" or "sheen" patterns are the least valuable. The ultimate pattern is the extremely rare and valuable "harlequin" with a symmetrical square checkerboard appearance.
Misconceptions
1. Opal is not soft. It has the same hardness as glass.
2. Opal is not unlucky. This was a rumour started about the year
1900 by London diamond merchants to try to protect their then monopoly. For centuries before that, opal had been considered a stone of good fortune.
3. Opal does not shrink in settings.
4. Opal does not lose its colour in the sun or snow (or anywhere).
5. Opal is not affected by water. However, in the past, triplets have been glued with a resin that does not agree with moisture. This resin has come apart, causing the opal to appear cloudy. Most triplets now have a water resistant glue so check this before purchasing, and always obtain a guarantee.

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35.21.8 Classify igneous rocks in hand specimens
After Al Grenfell The Australian Science Teachers Journal Vol. 32 No. 3
See diagram: 35.21.1a | See diagram: 35.21.1b
Use a magnifying glass to classify magmatic rocks by texture and mineralogy. Volcanic types and plutonic types of igneous rocks have cooled and solidified at different rates typically in different physical environments giving different textures. Plutonic rocks are the granites, some porphyries and other igneous unstratified crystalline rocks thought to have formed at great depth and pressure in the earth.
Plutonic rocks have individual grains coarse enough to be individually identifiable usually >1 mm diameter.
Volcanic rocks have no visible crystals
Classify plutonic rocks using the modification of the IUGS (International Union of Geological Sciences) classification of plutonic rocks. Use the triangular coordinate system in diagram 35.21.1a. Use diagram 35.21.1b to estimate the volumetric abundance of the major rock forming minerals. Divide the surface and sub volcanic magma systems of volcanic rocks into two broad categories with differing flows of energy and modes of eruption: the magmas are (a) blown out as pieces of ejecta or (b) erupted or intruded as coherent units. So you can distinguish corresponding hand specimens on the presence or absence of volcaniclastic texture. Table 1. shows the chief types of pyroclastic rocks. Table 2. shows classification of non-fragmented volcanic rocks, e.g. aphyric lava by colour. Table 3. shows classification of porphyritic volcanic rocks by phenocryst assemblages. Each table can be expanded to accommodate additional volcanic rocks that may be relatively uncommon generally but locally abundant.

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Classification of igneous rock hand specimens
1 a. fine grained < l. mm aphanitic . . . Volcanic rocks
1 b. average grain diameters > 1 mm phaneritic - Plutonic rocks . . . Go to 5 a 5 b
2 a. pyroclasts present . . . Pyroclastic rocks . . . See Table 1
2 b. pyroclasts absent; grains interlocked . . . Non-fragmental volcanic rocks
3 a. ground mass glassy . . . Obsidian
3 b. ground mass crystalline
4 a. aphyric phenocrysts absent . . . Aphyric lava . . . See Table 2
4 b. porphyritic phenocrysts present . . . Porphyritic volcanics . . . See Table 3
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1 b. average grain diameters > 1 mm phaneritic . . . Plutonic rocks
5 a. medium to coarse grained . . . Plutonic rocks
5 b. pegmatite (>30 mm) . . . Pegmatite

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Table 1. Pyroclastic rock types
Rock type: Features
Agglomerate: Pyroclasts >32 mm blocks and bombs rounded pyroclasts predominant
Volcanic breccia: Pyroclasts >32 mm blocks and bombs; angular pyroclasts predominant
Lapilli tuff: Pyroclasts 4 - 32 mm and of any shape
Tuff: Pyroclasts < 4 mm and of any shape.
Ignimbrite: Welded tuff with unsorted nature > 50% fragments < 4 mm pumice clasts common often flattened and with frayed terminations

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Table 2.
Aphyric lava
Rock type: colour
Mafic lava: dark coloured
Felsic lava: light coloured

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Table 3.
Porphyritic volcanic rocks
Rock type: phenocryst mineralogy (Plutonic equivalent)
Basalt: +- olivine +- augite +- plagioclase (Gabbro)
Andesite: plagioclase +- mafic phases (Diorite)
Dacite: plagioclase +- quartz + mafic phases (Tonalite)
Rhyodacite: plagioclase + alkaline feldspar + quartz +- mafic phases (Granodiorite)
Rhyolite: alkali feldspar +- quartz +- mafic phases (Granite)
Trachyte: alkali feldspar + mafic phases (Syenite)

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35.40.1 Mapping contours, geological structures, erosion
After N.E. Austin The Australian Science Teachers Journal Vol. 33 No. 1
See diagram 335.9.1
1. Show relief on the map with contour lines. To develop skills in contour line interpretation by experimental means use landform models of the three fundamental surface forms: planar concave and convex. They exist in five spatial forms as in figure 1.
A. Make the five forms A to E from flexible white cardboard. Contour lines are lines joining places of equal altitude i.e. for small regions of the Earth's surface the intersection of equally spaced horizontal planes with the Earth's surface. For landform modelling you can produce such planes with plastic sheets held vertically or 35 mm slides e.g. S1 and S2 as in figure 2 with the back light or projector projecting horizontally.

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2. Project S1 horizontally on the five spatial surface forms A to E then look vertically down on to the models. You can vary the inclination of each of the models A to E from 10^o to 90^o. Also you can vary the concavity or convexity of models B to E if the white cardboard used to make them is flexible. The figure 3 shows what you see when looking vertically down using S1. In A B and C contour lines are straight lines on all surfaces that can be generated by the translation in space of any horizontal straight line moving parallel to itself. In D and E contour lines are curved on all surfaces that can be generated by translation in space of any straight line inclined to the horizontal moving parallel to itself along a curved path.

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3. Figure 4 shows what you see when looking vertically down using S2. In A B and C contour line spacing decreases with increasing steepness of the landform. Figure 3D and figure 4D show that if contour lines are concave when viewed from the direction of low altitude to high latitude the landform is concave. Figure 3E and figure 4E show if contour fines are convex when viewed from the direction of low altitude to high altitude the landform is convex. The same spatial forms described above can be used in developing concepts of outcrop in relation to geological structures as in figure 35. In these experiments the projector can be positioned to take into account varying orientations of geological structure and landform.

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35.40.2 Isostasy models
After N.E. Austin The Australian Science Teachers Journal Vol. 32 No. 3
See diagram 335.9.2
1. Make a tank from acrylic or glass sheet. Keep a clearance of 2 mm at the sides and ends of the tank. Make a water inlet at the base of the tank to helps filling and draining with a garden hose. Adjust the mass of wooden blocks of various lengths by inserting rolled lead sheet and float the blocks in a water tank e.g. use 50 mm x 25 mm redwood timber density 0.6 g cm^-3. Cut a basic length 38 cm long. Calculate its true volume, V. Multiply this volume by 0.7 to find its adjusted mass M. Drill a 9 mm hole centrally upward through the base. Cut a short length of 9 mm dowel to act as a sealing plug in this hole. Put rolled sheet lead in the hole to adjust the relative density to 0.7. Put on a balance the 38 cm block the prepared plug and the rolled lead sheet necessary to bring the total mass up to the calculated adjusted mass. Use lead shot in the final mass adjustment. Insert the prepared lead in the prepared hole after rolling the sheet to fit. Glue in the prepared plug.

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2. To make an Airy's model cut 15 lengths of the redwood timber between 38 and 19 cm long. Drill and prepare plugs as above. Calculate the adjusted mass M for each length as above or use formula: Ma LM / 38 where L length in centimetres M mass of density adjusted 38 cm basic length in grams. Adjust all lengths as before. Check all lengths in a one litre measuring cylinder of water by flotation.

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3. To make a Pratt's model cut the same number of lengths are cut as before. The shortest possible length now is 28 cm so cut the lengths cut are between 38 and 28 cm. Prepare all drilled lengths and plugs. Use a longer drill hole for short lengths because you must adjust all lengths to the same mass M of the basic adjusted 38 cm. The shorter the length the greater the relative density.

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4. To make an erosion block cut a 38 cm length of 100 mm x 50 mm timber. Cut away the top corners of this block using a fine saw. Join the off cuts back together using an aluminium plate. Replace this block in its original position and drill the plate and whole block for a suitable locating pin. Adjust this whole block to a relative density of 0.7 as above. Introduce the larger erosion block into the Airy model. Remove the four shortest blocks from this set and introduce this block near the centre of the array. Remove the cut away upper corner block to simulate erosion and observe the isostatic readjustment. Replace this cutaway to simulating snowfalls and observe the isostatic readjustment.

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History
These lessons were originally written and illustrated by Mr J. A. Sutherland, Faculty of Education, University of New England, Armidale, Australia and later edited by Dr J. Elfick, School of Education, University of Queensland, Brisbane, Australia or made available to UNESCO by PHYWE SYSTEME GMBH, Robert-Bosch-Breite 10, D-37070, Gottingen, Germany and edited by Dr J. Elfick, School of Education, University of Queensland, Brisbane, Australia, or are based on the lessons in the New UNESCO source book for science teaching, Third impression 1979, ISBN 92-3-101058-1, and edited by Dr J. Elfick, School of Education, University of Queensland, Brisbane, Australia, working under UNESCO Contract No. 8347201, 2001-12-15. Experiments 32 to 40 were written by Dr J. Elfick, School of Education, University of Queensland, Brisbane, Australia. The experiments in this file were reviewed and edited by soil scientist Dr R. C. Bruce in July, 2005.

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