Soil and Water Conservation

Agriculture and Rural Development (Phase-I/II)

Title

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The soils in the high precipitation areas of wet equatorial climatic regions are

1. High in humus content

2. Low in silica content

3. Rich in sodium and magnesium salts

Select the correct answer using the code given below.

2 only

1 and 2 only

3 only

1, 2 and 3

Explanation :

Climate is an important active factor in soil formation. The climatic elements involved in soil development are (i) moisture in terms of its intensity, frequency and duration of precipitation - evaporation and humidity; (ii) temperature in terms of seasonal and diurnal variations. Precipitation gives soil its moisture content which makes the chemical and biological activities possible. Excess of water helps in the downward transportation of soil components through the soil (eluviation) and deposits the same down below (illuviation). In climates like wet equatorial rainy areas with high rainfall, not only calcium, sodium, magnesium, potassium etc. but also a major part of silica is removed from the soil. Removal of silica from the soil is known as desilication.
In humid tropical and equatorial climates, bacterial growth and action is intense and dead vegetation is rapidly oxidised leaving very low humus content in the soil. Further, bacteria and other soil organisms take gaseous nitrogen from the air and convert it into a chemical form that can be used by plants. This process is known as nitrogen fixation. Rhizobium, a type of bacteria, lives in the root nodules of leguminous plants and fixes nitrogen beneficial to the host plant.