Is gypsum and dhaincha together a good way to reclaim my sodic patch with poor drainage?

For a sodic patch, gypsum plus green manure plus drainage is a sound combined approach, but the steps and the gypsum amount must come from a soil test, so start there. Sodic soil has too much sodium that ruins the structure, so water cannot move through it, which is why it stays waterlogged and crusts hard. Gypsum supplies calcium that replaces the sodium, after which the sodium salts have to be washed down and out, so drainage is essential, otherwise the salts you free just sit there. Growing a green manure like dhaincha, which tolerates sodic conditions, and ploughing it in adds organic matter that further improves structure and helps reclamation. The usual order is: get the soil tested for the gypsum requirement, apply the recommended gypsum and mix it in, give a leaching irrigation with the drainage open so freed salts leave, then grow dhaincha and incorporate it. This is a multi season job, not a one time fix. Get the exact gypsum dose, drainage plan, and crop sequence from your KVK based on your soil test.