Experiment to study the texture of soil
Answers
(a) Soil temperature:
1. Take a soil thermometer (Fig. 72), set it on the surface of the soil in sun and shade, and note the readings.
A soil thermometer
2. Burry the bulb of the soil thermometer in the soil at a depth of 10 cm for some time and note the readings at different timings.
3. Now burry the bulb at different depths, i.e., at 20 cm, 30 cm, 40 cm etc. for the same period and note the readings.
4. At different depths, note the readings both in sun and shade as in Table 4.7.
Soil temperature at different timings
(b) Air temperature:
1. Take an ordinary U-shaped minimum-maximum thermometer (Fig. 73).
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U-shaped minimum-maximum thermometer
2. Observe the readings at different timings (8 a.m., 10 a.m., etc.) and at different heights, and also in sun and shade.
Tabulate your readings in the form of following Table 4.8:
Air temperature at different timing
2. Experiment to study the texture of given soil samples:
What is soil texture?
Soil texture mainly depends on the size of the soil particles, proportion of the various particles and on the peculiar and specific arrangement of these particles.
The designation of various kinds of soil particles mainly depends upon the diameter of the particles which can be categorized as mentioned in the following Table 4.9:
Soil particles size and their designations
Requirements:
Different soil samples.
Method:
For knowing the soil texture a rough but easy method is to examine the soil under the thumb and the finger in moist as well as dry conditions. A hand lens may also be used for it. Different particles can be judged as follows:
1. Sand:
Particles can be easily seen. These are loose and coarse. In moist conditions, the sand can be squeezed and cast but on touching by hand the particles will separate. Size of the particles varies from 0.02 to 2.0 mm.
2. Silt:
It gives clotty appearance in dry conditions. The size of the particles ranges from 0.002 to 0.02 mm. in diameter.
3. Clay:
It is sticky when wet. It forms a long flexible ribbon when pinched between thumb and finger. The size of the clay particles is smallest (below 0.002 mm. in diameter).
3. Experiment to estimate the bulk density of the grassland and woodland soil:
Requirements:
Soil samples, khurpa or any other digging instrument, oven, measuring cylinder, physical balance.
Method:
What is Bulk Density?
The dry weight of unit volume of the soil is called its bulk density. It is expressed as gram per cm3. High bulk density is inversely proportional to the pore surface of the soil. The soils with bulk density (gm./cm3) varying between 1.1 and 1.5 are medium to fine-textured while those between 1.5 and 1.7 are coarse-textured. Alkaline soils usually have a bulk density above 1.7. The bulk density is calculated by the formula:
Bulk density (gm./cm3) = Weight of dry soil (gm.)/Volume of dry soil (cm3)
Under mentioned is the procedure to find out the bulk density of the soil:
1. Take soil samples randomly from an area from a depth of about 15 cm.
2. Dry the soil in an oven for about 24 hours at a temperature of 105°C.
3. Transfer a part of the dried soil to a measuring cylinder and determine its volume.
4. Determine the weight of the above volume of soil on a balance.
Results:
Find the bulk density of the soil by the formula mentioned above. Also determine the type of the soil by the details mentioned above.
4. Experiment to estimate the porosity of different soil samples:
Porosity:
Pores between the soil particles are of great importance for the plant growth because they contain air and water. Porosity of the soil depends upon the texture and structure of the soil, compactness of the soil and also on the organic content of the soil. It increases with the increase in the percentage of organic matter in the soil. It decreases with the decrease in the size of the soil particles. Porosity also decreases with the depth of the soil in the earth.
Requirements:
Balance, oven, soil samples, measuring cylinders, water.
Answer:
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