Blossom-end Rot

Blossom-end Rot. I believe one of my four Supersonic tomato plants is suffering from something called Blossom-end Rot. It's a little unusual in that 2 of the 4 plants are planted right next to each other, side-by-side and one of them is suffering from this problem while the other one appears to be fine and showing no effects of Blossom-end Rot; same with the other 2, they're fine.

Blossom-end Rot of tomatoes is a physiological disorder caused by a lack of sufficient calcium in the blossom end of the fruit. Applying too much fertilizer at one time or excessive nitrogen fertilization can result in blossom-end rot.

Here are a couple pictures of what ours look like -

I'm not sure what's caused this problem but I'm thinking of a couple things that may have contributed; The raised garden box they're in is new and so is the soil I used to fill it. I used a mixture of regular old soil, leave and grass clipping compost and manure from my chicken pen, which also has rabbit droppings mixed in too. Perhaps I used too much chicken manure, which is typically high in nitrogen or simply too much fertilizer - too rich maybe. However, you'd think it would have effected both tomato plants since they're planted side-by-side.

Well we won't be enjoying or canning with these particular tomatoes but the chickens love em, so I guess it's not a total loss. I will have the soil tested at the end of the season to see if we can't determine the problem and fix it before next spring. Live and learn...