Question

how does transplantation of onion seedlings increases its production

Answer 1

The depth at which the onion seedlings are transplanted determine its production. 

If the seedlings are transplanted very deep into the soil, the new bulbs that are formed tend to be quite narrow and also more in number. Sometimes, they also tend to split causing one bulb to grow as two bulbs.

On the other hand, if the seedlings are transplanted using shallow planting, the bulbs will appear to be fatter and smaller.