In agriculture, salinisation or salination of soil is mainly caused by which of the following practices?

Introduction / Context:

This question concerns soil science and environmental issues in agriculture. Salinisation or salination of soil refers to the build up of soluble salts in the root zone, which can severely reduce crop yields and eventually make land unproductive. Understanding the main human activities that cause soil salinity is vital for sustainable irrigation management.

Given Data / Assumptions:

• Soil salinity increases when salts accumulate faster than they are leached away.
• Irrigation water often contains dissolved salts such as sodium, calcium and magnesium salts.
• Poor drainage conditions prevent these salts from being removed from the root zone.
• The options discuss pesticides, erosion, excess irrigation, crop rotation and organic farming.

Concept / Approach:

In arid and semi arid regions, intensive irrigation without adequate drainage leads to rising water tables and evaporation at the surface. As water evaporates, dissolved salts remain in the soil, resulting in salinisation. If this process continues over time, a white crust of salts may appear on the soil surface. The key concept is that excess irrigation combined with poor drainage is the primary cause. Other practices like crop rotation or organic farming do not lead to salt build up in the same way.

Step-by-Step Solution:

Verification / Alternative check:

Case studies from irrigated regions like parts of Punjab, Haryana and arid zones around the world show that canal irrigation on poorly drained soils has led to salinity and waterlogging problems. Technical reports on soil degradation frequently highlight over irrigation and lack of drainage infrastructure as major contributors. In contrast, sound irrigation management with proper drainage systems and periodic leaching can reduce salt build up. This evidence confirms that excess irrigation without drainage is the main cause of salinisation in the agricultural context described.

Why Other Options Are Wrong:

Heavy use of pesticides can cause environmental pollution and toxicity but does not by itself create salt crusts or significantly increase soil salinity. Soil erosion by wind removes topsoil and nutrients but is a different type of degradation. Crop rotation, especially with legumes, generally helps maintain soil fertility and can even improve soil structure. Organic farming emphasises natural inputs and typically reduces chemical stress rather than adding soluble salts. These practices are not recognised as the main drivers of soil salinity.

Common Pitfalls:

Students may associate any intensive agricultural input, such as pesticides or fertilisers, with all forms of soil problems, leading to confusion. Others might think that soil erosion, being a serious issue, must be linked to salinity, but erosion relates to loss of soil rather than salt accumulation. The central idea to remember is the movement of water and salts: when irrigation water brings in salts and there is no effective drainage, salinisation is the natural outcome.

Final Answer:

Salinisation of soil in irrigated agriculture is mainly caused by Excess irrigation without proper drainage.