Correct Option
The correct option is (b).
Explanation
Salinization is the accumulation of water-soluble salts (such as sodium, potassium, magnesium, and calcium) in the soil profile. This process is common in arid and semi-arid regions, particularly where irrigation is practiced without adequate drainage. It is a major form of soil degradation.
Option Analysis
- Option (a) is Incorrect: Salinization negatively impacts crop production. High salt concentration in the soil solution increases the osmotic pressure, making it difficult for plant roots to extract water (a condition known as physiological drought). This stunts growth and reduces yields.
- Option (b) is Correct: When the accumulated salts contain a high proportion of sodium (a process often linked to alkalinization or sodification), the sodium ions replace calcium and magnesium on the soil exchange complex. This leads to the dispersion (deflocculation) of soil colloids. The dispersed clay particles clog the soil pores, destroying the soil structure and rendering the soil impermeable to water and air.
- Option (c) is Incorrect: A rising water table is often a cause of salinization (through capillary action bringing salts to the surface), rather than an effect of it. Salinization itself refers to the salt content, not the water level.
- Option (d) is Incorrect: The condition where water fills all air spaces in the soil is termed waterlogging. While waterlogging often precedes or accompanies salinization, salinization specifically refers to the mineral residue left behind, not the saturation of pores with water.
Key Takeaway: Salinization, particularly when involving sodium (sodification), degrades soil structure by causing the dispersion of clay particles. This results in the clogging of soil pores, leading to impermeability and poor aeration.