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Soil Investigation for Crop Development

6069 words (24 pages) Essay in Sciences

18/05/20 Sciences Reference this

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Soil

Background Information

Look around you. Soil covers almost all of Earth’s land. We walk on soil in the woods, in parks, even in our own backyards. Engineers build houses and buildings on its surface. Soil is the place where plants and trees grow, making it a big part of agriculture.

Soil contains air, water, minerals, biota and organic material. Its features depend on the parent material, climate, topography, organisms and time (1-2 cm/1000 years around Canberra)

Soil is home to millions of tiny soil organisms (living things), from one-celled bacteria to ants, earthworms, and other small animals. These organisms interact with one another, and with their environment (the world around them). Similarly, when the soil environment changes, soil organisms are affected.

Most importantly, soil is an important resource. Growing our food relies on farming, which relies on having good soil. Once soil is damaged, it is very hard to replace. For this reason, environmental factors that harm the soil (such as pollution, erosion, and other forms of soil degradation) can threaten soil quality. The study of soil helps give us valuable information as society struggles to find solutions to these problems.

Humans have always changed the soil in many ways, but today, we are changing the soil in ways never seen. Pollution, pesticides, irrigation, and global warming are all having major effects on the soil and its organisms. Scientists are trying to understand these effects.

Soil is a mixture of broken rocks and minerals, living organisms, and decaying organic matter called humus. Humus is dark, soft and rich in nutrients. Soil also includes air and water.

Organisms in the soil need air and water to survive. Having these essential materials – air, water, and organic matter – makes it possible for plants, bacteria, fungi and small animals like earthworms and insects to live in the soil.

All the living things in the soil, plus essential materials that these organisms use to survive, form the soil ecosystem. Scientists study the soil ecosystem because they want to understand how organisms relate to one another and to the environment that surrounds them.

Scientists who study the soil ecosystem – soil and the living things in it – are called soil ecologists. Soil ecologists study the soil ecosystem in a variety of ways. What these all have in common is that they rely on careful observation and measurement.

Introduction

What is soil?

Soil forms the loose surface of the land.  A lot of plants depend on the structural support of soil, they use it as their main source of water and nutrients(food).  Animals, birds and even humans also get a lot of their nutrients from soil.  It is vital for life on earth.

There are a whole range of different soil types.  Processes such as leaching, weathering and microbial activity can be combined to make these soil types.  Each different soil has their own strengths and weaknesses plant production.  Because there are so many types of soils, they are placed in classes based on their colour, profile, texture, composition and structure.  All soils are formed differently and as a result they will all be found in specific places on the earth, the earth’s immediate surface, mid and deep under the surface.  The soils which are mid and deep down inside the earth are usually protected from the climate and any environmental factors.  While the soil on the surface is more exposed.  It can be easily moved by the wind, washed away by water, broken down from the temperature changes and any human and animal contact etc.

How is it formed?

Soil is made up of a mixture of 45% minerals, 25% water, 25% air, and 5% organic matter which is a combination of humus, tiny living organisms and plant residue.

All soils are formed from ‘parent material’ which is the remaining residue at the earth’s surface.  These materials could be weathered bedrock, or smaller materials carried by the wind or rivers etc.  then overtime the sun, wind, water and living creatures help to change the original parent material into soil.

Over time as the soil develops, different layers form what is called a soil profile.  Most soil profiles have 2 main layers, also known as horizons: topsoil and subsoil however some soils exhibit 3 main layers. 

‘A horizon’ – humus rich topsoil: plant roots, earthworms, and other micro-organisms, it generally is darker then other horizons due to the organic materials. 

‘B horizon’ – clay rich subsoil: less fertile then the topsoil but holds more moisture, it generally is lighter in colour and has less biological activity than horizon A.

‘C horizon’ – underlying weathered rock: this is from where both horizon A and B formed.

Sometimes some soil profiles also have an ‘O horizon’.  It is the very top surface made up of mainly plant litter.

Why is soil important?

Soil is essential for the lives of many things.  It is the ‘home’ for plants to grow in, it’s a habitat for many different types of insects and animals, it works as a filtration system for the water on the surface, it stores carbon and maintains atmospheric gases (eSchooltoday, 2017).  Soil can be easily damaged and washed or blown away, so it needs to be carefully managed.  Soil is a valuable resource and an essential building block for the environment, so we need to know how to treat and manage it well. 

What are the components of healthy soil?

Minerals: there many different minerals inside soils.  Each mineral has their own task which helps with plant and soil health

        Carbon:

        Calcium

        Manganese

        Nitrogen

        Potassium

        Phosphorous

        Sulphur

Organic matter: this is made by dead and decaying plants and animals.  Organic matter results in humus, which is created after the organic matter is broken down by the micro-organisms

Water: micro-organisms require water for their metabolic process but like other animals

Air/atmosphere: half of the soil volume consists of spaces filled with air and water.  Different gases found in soil include:

        Oxygen

        Nitrogen

        Carbon dioxide

        Water vapour

Soil micro-organisms: in 1/3 of a cup of soil there are more microbes then there are people on earth.  Different soil micro-organisms include:

        Bacteria

        Fungi

        Algae

        Arthropods

        Nematodes

        Worms etc (Holganix, 2018)

Include a diagram with explanation of the soil food web.

A healthy soil has a very dynamic living system.  There are many different organisms that live in the soil which are beneficial such as fungi, bacteria, protozoa and nematodes.  Although these cannot be seen without a microscope there are millions of these tiny organisms, they all work together to provide plants with what they need in order to grow and survive.  the term for all these organisms is the ‘soil food web’ (Soil FoodWeb, 2019)

What benefits are there for farmers and gardeners in testing their soils?

Testing the soil has become on of the most important management practices for crop production on farms and in home gardens.  The environment benefits greatly from these improved practices.  Farmers also have many benefits from testing the soil.  Some of which include:

        Increased knowledge

        Increased production: after testing the soil, production of crops can be increased once the initial problems in the soil have been resolved

        Spend less: one benefit of testing soil means that farmers will be spending less on fertilisers, water and pesticides/pest control

        Circular economy: a circular economy will be produced meaning the waste goes back into the soil to help produce more soil

        Sustainable solution: agriculture plays a huge part in the economy and the world and testing the soils and producing a circular economy will have some strong, long term benefits on the world.

Activity 1 – Soil Texture Test

Background Information

Texture is the ‘feel’ of the soil. This will depend on the various sizes of grains that make up the soil and the proportions of different sized grains. The different amounts of these particles, or grains in a soil sample are used to classify soils into a texture group. These groups range from pure sand to pure clay. Soil texture affects:

        how the soil holds water

        how water can seep down into the soil (porosity)

        what happens when the soil is cultivated (ploughed)?

The texture of soil is measured from the behavior of a small handful of soil after it has been moistened with water, kneaded and then using your forefinger and thumb, pressed to form a ribbon.

Aim

        to investigate some of the characteristics of soil by carrying out two tests on two different soil samples

        to compare the characteristics of soil samples taken from two different sites and see how the differences in soil might relate to the differences in vegetation

        to make knowledgeable recommendations regarding what could be grown successfully in the soil

Method

        Collect soil samples from two different locations in the school garden, fill two containers with each and label them (S1 and S2) In your workbooks, make a brief note of the main features of the sites from which you collected the soil

        Label each container with masking tape to identify the site – site 1 and site 2

Materials

        Two different soil types (clay, loam and sand)

        Water

        Soil Texture Key

        Pens/pencils

        30cm Ruler

Method: The Bolus and Ribbon test

  1. Take a handful of soil 1, enough to fit comfortably in the palm of your hand.  Remove or break up any stones, sticks or organic material.
  2. Add water, a little at a time and knead until the ball of soil just sticks to your fingers
  3. Continue kneading and moistening until there is no change in the soil ball
  4. Use the chart to determine the type of soil you have
  5. Now press the bolus between your thumb and forefinger so that it forms a ribbon
  6. Photograph the bolus and the ribbon to include in your report
  7. Measure the length of the ribbon (use a ruler) – only the length of the part of the ribbon that is not broken. This tells you the texture of your soil.
  8. Look up the ribbon length in the table on the next page and determine the texture of your soil.
  9. Use the chart to determine the texture class of your sample.
  10. Record results in the table on the ‘Results table’.
  11. Repeat steps 1 – 10 for soil 2.

Results

Table 1: Ribbon and Bolus test results

Soil Number

 

Notes

 

Soil type

 

Bed 2

(near the old raspberry vine)

 Sandy, obvious grains.  Ribbon 3.5cm

 Sandy clay loam

 

Bed 8

(in front of the tool shed, close to the oval)

 Very sandy, sand grains.  Ribbon 2,5cm

 Sandy loam

 Bed 2       Bed 8

 

The ribbon and bolus test for bed 2 left me with the following information and knowledge on this sample of soil:

The ribbon size for the sample from bed 2 was 3.5cm (35mm).  This indicates that the soil type is a sandy, clay, loam.  The bolus is sandy to touch, medium in size and there are visible grains in the bolus.  The approximate clay content is below 25%

The ribbon and bolus test for bed 8 left me with the following information and knowledge on this sample of soil:

The ribbon size for sample 8 was 2.5cm (25mm).  This indicates that the soil type is a sandy loam.  The bolus is very sandy and gritty to touch, and the sand grains are clearly visible.  The approximate clay content is between 10-20%

Activity 2: Measuring soil pH

Background Information

Soil pH is an important concern for farmers and gardeners for a range of reasons as it affects soil health and the plants and animals that live in it.

The measurement of soil pH tells us how acidic or alkaline the soil is. The range used for measuring pH is a scale from 0 (acid) -14 (alkaline). A pH of 7 is neutral. pH is dependent on the activity of hydrogen ions (H+) in solution.

A low pH measurement in soil may result in:

        Some minerals in the soil becoming soluble and reaching toxic levels for plants

        Some minerals made more available to plants

        The reduction and/ or killing of some bacteria which are important for sustaining plant life

        The encouragement of some molds

A high pH measurement in soil may result in:

        Some minerals being made unavailable to plants

        Some minerals becoming more available and possibly toxic to plants

        Discouragement of beneficial bacteria

        Favoring conditions for decay-causing bacteria

Field test kits used in this activity use colour to indicate pH levels. Test kits will tell you whether your soil is acid or alkaline. The pH of the soil can be changed slowly, over a period of years, if managed correctly,

Soil acidification

Soil acidification is a land degradation issue. Soil acidification is a natural process, accelerated by some agricultural practices. Without treatment, soil acidification will have a major impact on agricultural productivity and sustainable farming systems.

Soil acidity occurs naturally in higher rainfall areas and can vary according to the landscape geology, clay mineralogy, soil texture and buffering capacity. When plant material is removed from the paddock, alkalinity is also removed. This increases soil acidity. When grain, pasture and animal products are harvested from a paddock, the soil is left more acid.

More significantly, soil acidification is most often a result of nitrate leaching. Nitrogen is added to the soil in several ways e.g. nitrogen fixed by legume-based plants; as nitrogen-based fertilizers; from breakdown of organic matter; and animal waste.

Bacterial populations generally prefer a slightly acid environment. However highly acidic soils can inhibit the survival of useful bacteria, for example the rhizobia bacteria that fix nitrogen for legumes. As the soil acidifies, the favorable environment for bacteria, earthworms and many other soil organisms is degraded. Acid soils have a major effect on plant productivity once the soil pH falls below 5.0:

        pH 6.5 – optimum for most plant growth; neutral soil conditions; some trace elements may become unavailable

        pH 5.5 – balance of major nutrients and trace elements available

        pH 5.0 – aluminum may become soluble in the soil depending on soil type; phosphorus combines with aluminum and may be less available to plants

        pH 4.5 – manganese becomes soluble and toxic to plants in some soils; molybdenum is less available; soil bacterial activity slows down; aluminum becomes soluble in toxic quantities

        pH 4.0 – soil structural damage begins to occur

Aim

To test soil pH and discuss how pH effects plant growth

Materials

        pH test kit

        pH meter

        2 different soil samples

        White tiles

Method: The Soil pH Test

  1. Take ½ teaspoon from one soil sample and place on the white plate.
  2. Mix a few drops of the indicator solution into the soil. A thick paste texture should be achieved.
  3. Create a thin cover of the barium sulphate powder over the soil and indicator solution paste.
  4. Leave mixture for 2-3 minutes. During this time the colour should develop.
  5. Using the colour chart, match the colour that has developed with the soil, indicator solution and barium sulphate powder mix.
  6. Record the corresponding pH value in the Results table provided.
  7. Repeat the activity, using more of the same soil sample. This time use a pH meter to determine the pH.
  8. Record results into the Results table provided.
  9. Compare results obtained from the colour chart and the pH meter.
  10. Repeat steps 1 – 9 for other soil sample.

Results

Table 2: Soil pH results

Soil Type

pH using

indicator solution

pH using pH

meter

Notes

  Bed 2

 8

 N/A

 Purple = pH 8

 Bed 8

 6.5

 N/A

 Green = pH 6.5

Soil pH is a way to measure how acidic or alkaline the soil is.  It is a measure of the number of H+ ions in the soil water, pH stands for potential Hydrogen.  The pH is measured on a scale from 0 – 14.  0 being the most acidic, 7 being neutral and 14 being the most alkaline (The Compost Gardener, 2019).

The above chart shows the possible results for the pH liquid indicator test.  The results for both my samples of soil were ‘suitable’ results.  For bed 2, the pH reading came back as a purple which I matched to the pH 8.  This is actually quite high for a vegetable garden.  Usually growing vegetables will ideally need a pH of 6.5 however a pH between 6.0 and 7.0 is suitable for vegetables.  However, the growth will be affected if the pH drops below 5.5 or rises above 7.5.  if this happens treatment and modification is needed (E.J Penas and Dale T. Lindgren, 1990).  For bed 8 the pH was 6.5 which is in the middle and closest to a neutral pH level.  Which are the ideal growing conditions for vegetables.

To raise the pH of acidic soils:

Lime is usually what is used to raise a soils pH levels.  Either calcitic or dolomite lime can be used.  Calcitic limes adds calcium and dolomite lime adds both calcium and magnesium.  Adding lime will slowly but surely change the pH levels.  The amount that needs to be added will depend on the different soil textures.  For soils that are sandier, use less lime but add it more frequently

To lower the pH of Alkaline soils:

Composting should firstly be used in attempt to lower pH levels.  Although, sulfur is usually what is used to lower a soils pH levels.  Very little amounts of sulfur are required but time is key, it will take time.  The way it works is sulfur + time + soil bacteria = lover pH levels.  The amounts of sulfur needed will again vary depending on the solid types.  In sandy soils much less, sulfur is needed then in other soils (The Compost Gardener, 2019)

Activity 3: A Drainage Test

Aim

To determine the drainage properties of the soil

Method

Percolation Test (Drainage Test)

  1. Dig a hole approximately 40cm deep and at least 15cm in diameter.
  2. Fill the hole with water and leave to drain overnight.
  3. Fill the hole with water again and watch how fast the water drains.
  4. If the water sits in the hole it’s poorly-drained.
  5. If after an hour the level has a couple of centimetres, it’s moderately well drained.
  6. If it drains faster than that, it’s considered very well-drained.

Results

Soil sample

Drainage time

Notes:

Bed 2

29 minutes

This bed took longer to drain because of the higher amounts of clay in the soil

Bed 8

18 minutes

This bed was faster at draining because the percentage of clay was less in this bed of soil

Table 3: Percolation test results

Bed 2 (after 10 minutes)    Bed 8 (after 10 minutes)

 

The above picture is known as a texture triangle.  If the percentage of sand, clay and slit in a soil sample ae known, lines can be drawn into the triangle to work out what textural category the soil belongs to.  The soil from bed 2 falls in the sandy clay loam and the soil from bed 8 falls in sandy loam.  Both soils have a high percentage of sand, and clay and very low – no percentage of slit.

The particle sizes of soil are what determines how well the garden is drains water.  Proper drainage is essential for the survival of plants, they need a good balance between air, and water in the soil.  Some plants can survive in dryer soils that drain water fast and some can survive in soils that hold the water more temporarily.  However, most plants need well-draining soils to grow. 

If the water from the percolation test has completely drained with 10 minutes, then the soils is dry and isn’t ideal for most plants.  If the water is draining out with 30 minutes, it is still draining fast however it is still okay for plants that prefer well-drained soils.  If the water takes between 30 minutes and 4 hours to drain this is generally the ideal water drainage.  Most plants will thrive if living in this drainage situation.  Any water that is still draining after 4 hours means that the soil in poor at draining water and plants most likely won’t survive in this type of soil (dummies, 2019).

Any water drainage conditions can be improved by adding organic matter.  Organic matter such as any living or dead animals, and planter material.  Adding organic matter to the soil will help the fast-draining soils retain more water and poorly draining ones to dry out faster. 

Based on this it appears that both bed 2 and bed 8 are draining too quickly.  Bed 2 was completely drained in close to 30 minutes.  This is an example of a well-drained soil, which a lot of plants will be quite happy to live in and will be able to survive.  Bed 8 is an example of a dry soil.  To the eye it did not appear to look dry however after performing the percolation test the results are showing that it is classed as a dry soil because it is draining so quickly. 

Discussion

What do the three soil tests tell us about our soil in the school garden?

There are several reasons while soil testing is important.  It gives an understanding of how to optimize crop production, protect the garden of un-necessary and excess fertilisers, it can help diagnose problems with plant growth, improve nutritional balance of plants. 

After collecting the results from the 3 tests a lot of information can be gathered about of school garden.  The overall results from bed 2 show that it is a sandy clay loam.  This explains why it took longer for the water to drain when doing to percolation test.  The pH in the soil was rather high in alkaline which is usually a problem for most vegetables, as they generally thrive in soils with a more neutral pH level.  The results for bed 8 show that it is a sandy loam.  This explains why the water from the percolation test drained relatively quickly because the amount of clay in the soil is quite low. 

Do we need to make any changes?

The results from the tests for bed 8 are all relatively positive results.  The pH levels are neutral which is what most plants thrive in.  The only change that could be made for bed 8 is adding organic matter such as living and deceased animals and plant materials which would assist in stopping the water from draining from the soil so quickly.  A change to garden bed 2 needs to be made, as the pH levels are too high.  The pH levels need to be lowered to help increase crop growth.  This can be done by adding small amounts of sulphur and by composting. 

How could we go about improving the quality (texture and pH) of our soil?

The quality of the pH in soils can be improved by testing the soil pH to ensure it is between 6 and 7.  If the soil is above 7 it means the soil has too much alkaline.  To fix this increase the acidity of the things that are being added to the soil.  Thins like compost, manures, leaf litter, mulch etc.  If the soil is below 6 then it means it is too acidic.  To fix this add lime or dolomite, manure can also be used (gardening Australia, 2019).

Changing a soil’s texture is very difficult, however improving a soils texture is a bit easier.  Clay can be made or porous, sand can be made more water retentive by making some simple adjustments.  The best thing for any soil is organic matter.  As the living and decaying plants and animals decompose, they release nutrients that are absorbed by the soil’s microorganisms and bacterias.  For clay-based soils the tightly packed particles are forced apart which improves draining.  In sand it acts as a sponge an assists in slowing down the draining process (Sunset, 2019).

Give some reasons for any differences in your pH results

Changes and differences in pH levels are generally the result of a loss of organic matter, removal of soil minerals when plants are being harvested, erosion of the surface area, and the effects of nitrogen and Sulphur fertilizers (USDA, n.d.). 

The differences in the pH levels between bed 2 and bed 8 may be because of the different types of crops and plants being grown in the beds.  How often crops in each bed are being harvested from each bed may also have something to do with the different pH levels.  The types of manures and organic matter in each soil will change the pH levels.

How well are plants likely to grow in each of these soils? Comment on the texture, the pH and the drainage capabilities

Most plants prefer a neutral pH level of around 7.  When a plants soil pH increases the plants ability to absorb certain nutrients is disrupted meaning that not all nutrients can be absorbed properly (SFgate, 2018). 

What would you recommend be grown in each location, assuming the conditions remain the same?

Assuming the growing conditions remain the same the best vegetables for bed 2 are asparagus and garlic because they can grow and survive with the pH level of 8.  The best vegetables to grow in bed 8 are broccoli, cabbage and spinach with a pH level of 6.

Conclusion

Overall, we did achieve the aim to investigate the characteristics of soil by carrying out 3 tests on two different soil samples.  I compared the characteristics of the two soil samples from the different beds to see how the soil differences relate to the differences in vegetation.  After thorough research, I was able to confidently make recommendations about what crops could successfully be grown in soil.   

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