A piece of redland

Dhaka,  Mon,  29 May 2017
Published : 19 May 2017, 21:10:24
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A piece of redland

Nutfa Zakia Nehrin
The students of the Department of Soil, Water and Environment at the University of Dhaka, recently made a field trip to Purbachal near Rupganj on the north-eastern side of the capital. As a student of that department this scribe had the privilege to see there the red and terrace land. We had been there to examine the soil horizons and other characteristics.

A piece of redlandThe parent material of the soil is the Modhupur clay; this soil is a marine deposit of the Shitalakhya river. This is unusual because there is no red soil around Purbachal. Moreover, Modhupur is far away from Rupganj. This is a 'Pleistocene terrace' which means the soil particles from the Shitalakhya river were deposited more than 1.0 million years ago to form the terrace (land which is about 12-15 feet high from the sea level). That was really astonishing! We touched something which was one million years old. This soil offers easy drainage of water for irrigation as well as precipitation. Therefore, people there just do not experience floods. Moisture of the soil varies from layer to layer, e.g. while the top soil is dry, sub-soil and sub-stratum layers are moist. It contains concentration of iron and manganese.

Moreover, due to urbanisation, the terrace has been cut down. As a result, its height often drops to about 4-5 feet. But despite these limitations, the advantages are overwhelming. The soil is very suitable to vegetations. Mango, jackfruit, lichi trees, bamboo and many other plants and crops grow here.

Though there is a little difference between a soil horizon and a layer, horizons have distinct characteristics. Generally, soil horizons are determined by observing different colours of soil layers. A horizon contains soil particles of the same colour. It is important to mention that there can be 164 colours to describe soil. The soil of our experimental region shows little variations in colours of horizons. So, difficulties are there.

How could we determine the horizons? As per directive of our teacher Professor Md. Aminur Rahman, we determined and distinguished the horizons by their hardness or softness. The top layer (A) is black in colour, then there is a layer (B) of 10-40 cm, which is little hard, yellowish red in colour. Then came a soft layer (B2) of about 40-90 cm and of the same colour. Again came a hard layer (B3) of 90-110 cm and finally came the last horizon (C) which contains mottles (spots of different colours).

The reason of the soil being red is oxidation of iron. When iron is oxidised, it forms ferric iron oxides which are red in colour. The soil is clayey. The percentage of sand and silt is low. So, the plasticity of the soil is very high.

It was a huge amusement to be there for observing the soil characteristics. The experiences we gathered from the field trip just could not be thought of before. Studying a subject related to nature can be more interesting rather than studying a subject related to technologies or arts.

The writer is a student of Department of Soil, Water and Environment at Dhaka University.                          

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