Thanks for the question sir.
Mulching of the soil with suitable materials reduces water loss and frequency of water application. Also providing shade during hot and dry wind conditions reduces moisture stress.
I think gypsum can be used (through drip irrigation system or soil application) to reduce blossom end rot but first we have to make sure the main causes of calcium deficiency in tomato plant.

Main causes:
1. Plants are unable to uptake calcium from soil due to moisture stress
2. Calcium may not be available in soil
3. Some time calcium may be present in soil but unavailable to plants due to excess soluble salts (especially sodium).
4. Damage to the root system also make plants unable to uptake calcium and water.

Soil testing helps in determining the need for calcium application to soil.

Limestones is also a good source of calcium but should be applied to soil 2 to 3 months before planting.