Question

give reason organic wastes and earthworm are added to basic salts

Answer 1

Important Facts About Vermicasting
Turning organic wastes into casts takes 22–32 days, depending on density of waste and earthworm maturity (regular composting requires 30–40 days, followed by 3–4 months curing).
Vermicast does not need curing, but fresh casts undergo 2 weeks of nitrification where ammonium transforms to nitrate, a form that plants can uptake.
Use organic materials that meet the earthworm's feed preferences, including a material density of 350–650 g/L.
Worms should not be crowded, so the ideal stocking density is 150 earthworms/L of wastes.
Earthworms ingest about 75% of their body weight/day; a 0.2 g worm eats about 0.15 g/day.
If you discover earthworms trying to escape any system, it is a good indication that something is wrong with their feed or environment
Earthworms should be allowed about 1 week to migrate from finished vermicast to fresh waste.

Answer 2

This employs the process of vermicomposting in which earthworms or similar organisms are used to decompose the organic matter to form the vermi-compost.

This is done to increase the fertility of the agricultural soil. Organic matter and earthworms ( vermi compost) are acidic in nature and are therefore mixed with basic salts to form the perfect resultant mixture in order to facilitate the fertility of soil.