ᐅ Natural weed killer before topsoil is laid down

Hello
Today, the excavator removed the top layer of soil, including weeds and roots, and stored it on the side.
Later, topsoil will be added on top of this layer.
To prevent new weeds from growing, I would like to use a natural weed killer now so that they don’t have a chance to grow through the topsoil later.
What do you recommend? Rock salt?

If you search online, you will find vinegar, salt, and baking soda. However, these methods are not effective and may even be prohibited. On the other hand, some ready-made glyphosate-free herbicides contain acetic acid as the active ingredient.

Perhaps cover it with a tarp?

Black plastic sheeting is a good idea because:

thermal weed control is based on a biochemical principle: most proteins denature at a temperature of about 42°C (107.6°F).

If a "core temperature" of 42°C (107.6°F) can be reached inside the pile, everything should be destroyed. Compost heaps often get much hotter (70–80°C / 158–176°F).

please no salt – I believe a vapor barrier is the gentlest solution.
What is the surface area and the time period involved?
If there is a large sheet of plastic covering the area, no rainwater will penetrate the soil there, and during heavy rainfall, could that cause flooding... for the neighbors...?

World-e schrieb:

If you google it, you’ll find vinegar, salt, and baking soda.

All of that is unnatural for the surface and damages the soil.
You plant cover crops like a farmer, such as rapeseed, lupine, and similar plants. This protects the soil and helps form new nutrients. Taproots loosen the soil.