Q.Using Wet Rotted Straw?
I had a bin containing a good field straw, and over the winter it part filled with rain creating a deep rich brown liquid (that now smells like silage) and rotten straw. I have used the rotten straw as a composting base for growing potatoes, but am I likely to have problems if I apply the water the straw was soaking in to assist other vegetables (garlic, onions, beans, peas)?

Certified GKH Gardening Expert
Because it is questionable in what is, actually, in the water- I would not recommend using it...
Adding this may increase the risk of bacterial infection to the soil. Many bacterial infections are very difficult to get rid of, so adding them to the soil will be more trouble than it is worth.
Adding to a compost pile will be fine, though. With correct composting technique any bad bacteria will be killed off.
This article will offer more information on composting with hay:
https://www.gardeningknowhow.com/composting/ingredients/how-to-compost-hay-bales.htm