Iodine for soil?

My previous post about sub optimal iodine levels got me thinking about our soil. I add a trace element mix into our soil to increase levels of minerals in plants that we eat. However this trace element mix only has the elements that make the plants grow better or look nicer.

Therefore it doesn't have selenium nor iodine. I have am struggling to purchase some selenium based fertilizer. I can purchase 25kg bag for about $200, which is made for farmers to put on their soil, so their livestock stay healthy. However I only need 1kg which should do our soil for the next few years! It also doesn't have iodine.

Seaweed extract may contain iodine, so I think I will use this more, along with gathering seaweed when I goto the beach. However I am unsure if seaweed extract contains selenium.