1. The eighth square on the second row needed 256 spoons of rice, which amounted to a bowl.

Question

2. The eighth square on the second row needed 256 spoons of rice, and it amounted to a bowl.

3. The eighth square on the second row needed 256 spoons of rice, and they amounted to a bowl.

(Can ',which' be 'and it' or 'and they'?)

Answer 1

1 and 2 are fine and, yes, they mean about the same thing. 3 is not correct.