It is the only day with the distinction of a double blessing. If one were to consider this, then the Third Day would have three blessings. Salt presides over every karbon even this the most humble of offerings, the meal offering. Because Salt was created on the second Day. Because Salt has the power to alter whatever it touches.
Salt represents stability between opposing forces as in fire and water.
When these waters were separated the lower waters protested that they desired to be close to Hashem like the upper waters were. As a result G-d established the Covenant of Salt. Salt is the product of an alliance between fire from the sun and ocean water. The fire from the sun bears down upon the water. When man was created by G-d, man was formed from the dust of the ground.