Water Absorption in Soil

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Soil and Its Formation

The soil definition is something we are all well familiar with. The soil varies based on its composition and structure. In general, it can be defined as the material found on the surface of the earth, which is composed of inorganic and organic material. We have a number of soil types like loam, clay sand, silt, and more. Soil is made of fine rock particulates of different sizes. These are derived from the sedimentary and weathered igneous rocks after environmental factors such as wind, rain, heat, cold, and more related have acted upon the rock particles. This caused the rock particles to break down to smaller ones, which on the accumulation in flat or shallow surfaces eventually come to constitute the soil. Soil formation has been moving on this planet for a very long time, about billions of years ago. It seems to be a happening process that will continue as long as this planet exists.


Properties of soil

Percolation rate of water in the soil

  • Percolation is the property of the absorption of water by soil

  • If we pour a bottle of water in the soil and another bottle of water on the floor, the water on the floor will flow down, whereas the water in the soil will be absorbed

  • The percolation rate is simply the amount of water absorbed by any soil at any given time period

The formula to calculate percolation rate is given by,

Percolation Rate (ml/min) = \[\frac{\text{amount of water(ml)}}{\text{percolation time(min)}}\]

For example, if 200 ml of water is percolated through the soil sample in 40 min, we can calculate the rate of percolation as given below.

As we know,

Rate of Percolation = \[\frac{\text{amount of water(ml)}}{\text{percolation time(min)}}\]

= \[\frac{200 ml}{40 ml}\] = 5 ml/min


Absorption of Water in Soil

Take the sandy soil of extremely small-sized rocks, that is known for the aeration but not for the water retention. On the other side, clay soils have colloidal particles that can hold water, but they are very poor in aeration. The big sized rock particles do not hold any water between them. In fact, any such soil having rock particles that do not hold water in between them is not good for the development of a root system.

This is because the holding capacity of water in the soil is abysmal. However, if we are wondering which type of soil retains a maximum amount of water, then the soil is loam. Because loam provides proper capillary spaces and good aeration to hold water, it has a mixture of sand, clay, and decomposed organic material, known as humus. Therefore, this soil is considered to be the best for the growth of plants since it has a good holding capacity of water. Many other factors, such as permeability, infiltration rate, percolation, and more, affect the water absorption of soil also.

Water is present in the soil in five different forms. They are gravitational water, capillary water, hygroscopic water, water vapours, and combined water. The ultimate source of all soil water is irrigation or rainwater. An amount of rainwater does not enter the soil, but it is drained away from the soil-surface along the slope. It is known as either run-away water or run-off, which is represented in the below diagram.

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Let us understand the absorption of water by soil by an experiment.


Experiment on the Absorption of Water by Soil

This experiment will explain that all the soils absorb water either to the same extent or not.

Procedure

Take a plastic funnel and a filter paper (else, a piece of newspaper sheet). Fold and place it as shown in the below figure. Weigh 50 grams of powdered and dry soil and pour it into the funnel. Now, measure a certain amount of water using a measuring cylinder and pour the water drop by drop on the soil. We can also use a dropper for this process. And, remember not to let all the waterfall at one spot.

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Pour the water all over the soil and keep pouring till it starts dripping. Now, subtract the amount of water left in the measuring cylinder from the amount that we started with. The resultant water is the amount retained by the soil. Note the results in a notebook in a manner described below.

Weight of soil = 50 grams

The initial volume of water in the measuring cylinder = U mL

The final volume of water in the measuring cylinder = V mL

Volume of water that is absorbed by the soil = (U – V) mL

Weight of water absorbed by the soil = (U – V) g (1 mL of water has a weight equal to 1 g) percentage of water absorbed.

= \[\frac{(U-V)}{50}\] * 100

Where 50g is the amount of water absorbed.

We can also repeat the same experiment with different soil samples. By doing so, we can come to know which soil would have the highest and lowest percolation rate, which soil type retains the highest water amount and which retains the least at the same time. In addition to this, we can also know many more regarding different soils.

FAQ (Frequently Asked Questions)

1. How is the soil prepared, and why the horse dung is mixed in the soil while preparing?

Ans. Dry soil will be placed in a big sized tank and would be cleaned of pebbles. After removing such things, the soil will be soaked around for eight hours. Then, such soil would be kneaded after mixing the horse dung. The kneaded soil and then it would be placed on the wheel and produced an appropriate shape. The final shape is given using the hands. The items are coloured as per the necessity after three days of drying. All the prepared items are baked at high temperature after drying in the air.

The burnt horse dung is mixed in the soil because it helps open up the pores in the soil. By doing so, the water could percolate out of the surahis and matkas, and evaporate, and then cool the inside water. We know that Sohagpuri surahis and matkas are famous in far off places such as Nagpur, Jabalpur, Allahabad, and in some other places.

2. Explain the moisture in Soil?

Ans. The moisture in the soil can be explained by activity, as given below.

Procedure

Take a boiling tube and put two spoons full of a soil sample in the tube. Heat it on a certain flame and observe. Let us find out what happens when it is heated.

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On heating, the water present in the soil evaporates, moves up, and then condenses on the cooler inner walls of the upper part of the boiling tube. Whereas on a hot summer day, the vapour that is coming out of the soil reflects the sunlight, and the air above the soil seems to shimmer. Once the soil is heated, take it out of the tube and compare it with the soil which has not been heated. We can notice the difference between the two soils easily.