In India, a large tract of agricultural land has lost its fertility due to various reasons. Wich of the following is NOT such a reason?

leaching

The correct answer is option 4: leaching

Alkalisation, salinisation, and waterlogging are major causes of loss of soil fertility in India, especially in irrigated regions.

Leaching is a natural process in which nutrients are washed down into deeper soil layers due to heavy rainfall. Although it may reduce nutrient content in some soils, it is not listed among the major causes responsible for large-scale loss of agricultural fertility in India

NCERT:Degradation of Cultivable Land- "One of the serious problems that arises out of faulty strategy of irrigation and agricultural development is degradation of land resources. This is serious because it may lead to depletion of soil fertility. The situation is particularly alarming in irrigated areas. A large tract of agricultural land has lost its fertility due to alkalisation and salinisation of soils and waterlogging. Excessive use of chemicals such as insecticides and pesticides has led to their concentration in toxic amounts in the soil profile.