Spent barley mulch +wall of water = vinegary plant death

Last year, I mulched with spent barley from a local brewery. It was great. It's free, natural, easy to spread, gives good cover, stays in place relatively well, and eventually breaks down to provide nitrogen, etc back to the soil. In fact, I still recommend it. However, I wouldn't recommend doing what I did this year:

I got the barley from bins outside the brewery early one morning (gotta get there before the flies do). The barley was still wet and stinky from brewing. I went straight to my community plot, removed the black plastic mulch (weather had definitely warmed up enough) and began spreading the barley around. I put a good 2in layer on top of the soil. This was all fine. The problem came when I a) spread thick wet layers around some of my smaller plants, all tomatoes; these were my 2nd round transplants that I planted where I realized there was room after the 1st round, then b) put the walls of water back around these small tomatoes.

I go back the next day to check on things, and what do I find? Brown, shriveled tomato seedlings. Completely gone. The walls of water around the wet barley had created a hot vinegar tomato-annihilation atmosphere as hospitable to plant life as the ammonia clouds of Jupiter. The tomatoes never had a chance. This pic is the Early Girl tomato, after 1 day in my unintentional death chamber. Look closely; the leaves are reduced to papery dead shreds. This was the largest of the condemned tomatoes. The stem of this one lived (the others were smaller so got totally boiled), but since I have so many plants at home, I pulled it out and replaced it with another fully-alive plant.

Didn't see this one coming!
Lessoned learned: it always pays to have 3x the plants you really need ;)

-jardinera de muerte