The soda bottles the way you want to use them are mini greenhouses and would be too hot to leave on all summer. Once the leaves touch the sides they will burn. They are great for warming the soil, protecting plants from frost in the spring and for starting frost hardy plants earlier.

I don't know what made you think you could plant closer if you used them. A plants roots need the same amount of space whether or not they are covered with anything.

If you want to have more room in the garden then think of having some vining plants and have them grow upwards on trellises or chicken wire secured on sturdy posts. You can make a teepee with bamboo poles stuck in the ground and tied at the top.

On these you can grow cucumbers, peas, pole beans, and vining tomatoes--make sure they are vining not bush varieties. I'm sure there's more but I can't think of them right now. Maybe someone else can add to my list

"I want to use soda bottles, 2 liters, to plant in burying them with the bottom open, so to plant things closer."

It sounds like you are using the bottles as bottomless pots to contain the root growth of the plant. Am I understanding that correctly?
If so, you are going to end up with root-bound plants which do not thrive nor produce as well as those who have sufficient space.
Oilpainter's idea of trellising plants such as cucumbers, squash, pole beans and even small melons will save you space. Succession planting (lettuce, followed by beans, followed by broccoli, for example) will utilize your space well, too.
Making the hard decision on what to plant and giving the plants space to grow will result in a better garden than a bunch of plants that are competing for space or are root-bound.

Thanks! I was thinking along the lines of what a raised bed garden would do, so without the extra raised bed soil, it seems to be a worthless to do what I want.

What about using them as mini raised beds? The plastic would dry them out and kill them in this somewhat hot climate, but a planter next to a plant, it shouldn't bother them. I should just cover them in relfective white paper, do you think that would cool the plastic bottles off?