Establish what types of soil holds the most water and to see if changing a certain variable such as the ph value of the water has any effect on how much water each type of soil will hold.

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Charlotte Swain                                                                                                            Biology Homework


The aim of the experiment is to establish what types of soil holds the most water and to see if changing a certain variable such as the ph value of the water has any effect on how much water each type of soil will hold.

Background Information

Many factors might affect the absorbency of soil, some affecting only certain types of soil in particular. For example the obvious influences such as the amount of soil and the amount of water added to it will certainly limit how much water the soil can hold and the amount able to pass through. However, there are also other less apparent aspects that might also have an effect on the limit of water different soils can hold. For example the size of the soil particles might have an influence because if the soil is in large chunks that leaves gaps in between them then the water may just filter straight through so little is absorbed by the soil. On the other hand, if the soil is in a fine grained sand this might trap the water because there is little space between the particles causing a lot to be absorbed. Foreign bodies in the soil such as debris, small pieces of litter, chunks of clay or rocks and even the amount of glass wool used may also effect the absorbency by either blocking the funnel so that the outlet is blocked causing the water to be trapped in the filter under the soil with soil floating on top - though the water is not actually absorbed, or, if the outlet is not blocked helping the water to drain easily through the soil so that it hold less.

Another factor which may effect it is the temperature of the water, according to particle theory, the water particles have more energy and move faster if the temperature is higher causing more particles from the surface to escape into the air as they evaporate, thus meaning that less is held in the soil because it is constantly evaporating at a quicker rate. What is more, the water which does actually come through the beaker may also evaporate before it is measured so again distorting the results. And at the other extreme if the water is cold or near freezing, frozen particles within it will not be able to be absorbed into the soil as they are solid and to large meaning the soil holds less, however, they also won’t be able to pass through the funnel either. This means that temperatures at the extremes for water (0 or 100 degrees Celsius) are quite difficult variables to measure.

Micro organisms in the soil such as small living insects or parts of plant stems etc. may absorb some of the water themselves making it appear that more has been held within the soil, again affecting its recorded absorbency. Another factor which would be interesting to see if it had any effect on the soil would be the ph value of the water added, as, possibly if the water was very acidic or alkaline this may have an effect on how quickly it evaporates or even possibly if it reacts with any of the properties in the soil causing a chemical reaction to take place so that new products are formed and maybe even gases given off which will reduce the amount of water passing through the funnel. It would be another test to see if acid or alkaline react the best with different sorts of soil and then compare the results to how they effect the absorbency. Finally, the salt content of the soil may also have some effects whether it is because large salt crystals help filter the water, fined grained salt traps it or even that the salt gets absorbed into the water thus reducing the overall mass of the soil meaning that less water can be held within it, plus the fact that the amount of salts dissolved in the water affect its movement through the soil which may mean that it will run quicker through a larger mass or on the other hand get trapped more easily in spaces, both affecting the water passing through and final result for the soil absorbency.

Prediction and Hypothesis

This prediction is going to be based on two different variable which are the different types of soil: clay, sandy, woodland and peaty and the different ph values of the water added: strongly acidic, neutral and strongly alkaline which means that their will be 12 results three for each type of soil.

The prediction is that the clay soil will absorb the most water because clay has a large surface area and is very thick allowing it to take up large amounts of water by causing some water to cling to it (adhesion.) Clay will also swell as it absorbs water because the particles in it are very fine as a result making its water capacity higher. After clay, peaty soil will most likely hold the largest amount of water because it is also finely grained yet more compact than clay and not as malleable and stretchy. Peat also contains a lot of decomposing mass and organic matter as well as moss which may help it to hold more water if the matter absorbs some of it. Third, after peat will be the sandy soil because although the grains are very fine which might cause some water to be held, the grains don’t swell like peat and clay to form slippery reservoirs and usually the water just filters through even though it can take a long period of time. However, sand usually does contains a lot of salt which can affect the movement of the water causing it to move more slowly through the grains which may mean that less gets through in the time space allocated for the experiment. And, lastly it is predicted that woodland soil, which in England is known as heavy soil because it is rough and compacted, will hold the least water. Woodland soil usually contains fragments of roots and small rocks mixed with fine grained compost which means it holds less water as the water usually drains through the larger pieces. However, some woodland soil can contain decaying matter that can help to trap water in gaps between the layers.

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The other part of the prediction is whether the ph values of the water added to the different soils affects the absorbency. It is predicted that a neutral solution will cause the highest amounts of water to be absorbed mostly in clay, then peat, then sandy and finally woodland ensuring that the properties of the different types of soils above still apply. It is probable that making the water alkaline will have more affect than making it acidic so water with an alkaline solution in it will cause the soil to absorb more water. This prediction is based on the ...

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