Fluctuations in the temperature, fertilizer levels, or amount of water can cause the tomatoes to grow in spurts rather than at a gradual pace. A plant goes through a “hardening off” period after it has a spurt of growth, which would not occur if all of the growing elements (fertilizer, water, heat, etc.) remained somewhat constant. This “hardening off” happens to the fruit and the skin. Once the skin has hardened off, if the fruit has another growth spurt, the skin will not be able to stretch to contain the fruit inside it, hence the cracking or splitting.
http://greensideupblo...nd-spliting-tomatoes/