Other conditions that interfere with calcium uptake can cause calcium to be demanded in higher quantities than the plant can physically supply. Use a nitrate nitrogen rather than one that releases nitrogen in the ammonium form. Excess ammonium ions reduce calcium uptake. Also make sure that the plants are not overfertilized especially when the fruit are small. Maintain even soil moisture.
Mulches conserve moisture and moderate soil moisture extremes.
Even with mulches, weekly irrigation will be necessary if there is no rain. Fluctuations in soil moisture often leads to an increase in blossom-end rot. Make sure tomatoes are planted in an area with good drainage. Excess water causes roots to smother leading to reduced calcium uptake. Do not hoe too deeply.