An effective way to kill weeds is to pour salt water on the ground around the plants.?

Plants (weeds) require water uptake (by osmosis). By pouring salt, you decrease the water potential (concentration of water) in the soil. This means that water potential in the soil is lower than that in plants, Therefore, according to the rule that osmosis bides by, water moves from a region with high water potential to a region with low water potential along a water potential gradient. So, water from the weeds will flow out of the weed plant to the soil. Without water, weeds (plants) would die.

Water Potential Gradient just means an area with lots of water particles (e.g. pure water) to an area with few water particles (e.g. sugar dissolved in water)

Salt Water To Kill Weeds

It is indeed osmosis. The salt water is hypertonic to the root cells of the weed. This will cause water to flow out of the root cells into the soil, causing the cells to collapse and die, thus killing the weed.

Salt draws water from the plant via osmosis (water moving from high->low concentration) with no water the plant will die

No that is not effective because in 10 years nothing will grow there.