UPSC Prelims 2018 Question:

With reference to agricultural soils

consider the following statements:

1. A high content of organic matter in soil drastically reduces its water holding capacity.
2. Soil does not play any role in the sulphur cycle.
3. Irrigation over a period of time can contribute to the salinization of some agricultural lands.
   
   

Which of the statements given above is/are correct?

Explanation:

• Most soil organic matter originates from plant tissue. Plant residues contain 60-90 percent moisture. The remaining dry matter consists of carbon, oxygen, hydrogen and small amounts of sulfur, nitrogen, phosphorus, potassium.
  
  
• The addition of organic matter to the soil usually increases the water holding capacity by increasing the number of micropores and macropores in the soil either by “gluing” soil particles together or by creating favorable living conditions for soil organisms. So, statement 1 is not correct.
  
  
• The major forms of sulphur in soil include elemental sulphur, sulphides, sulphates, and organic sulphur compounds. Most of this sulphur enters the soil as soluble inorganic form produced during the weathering of minerals, from fertilizers and atmospheric deposition, and organic sulfur from decomposition of organic matter. So, statement 2 is not correct.
  
  

• Irrigation over a period may lead to increased rates of leakage and groundwater recharge causing the watertable to rise. Rising watertables can bring salts into the plant root zone. The salt remains behind in the soil when water is taken up by plants or lost to evaporation. So, statement 3 is correct.
  
  

Therefore, option (2) is the correct answer.

Subject: Geography | Agriculture and Allied Sectors(geo)