A question of blood and soil...

Curious to hear from others....

I did a quick Google search, and learned about blood meal, a kind of fertilizer that is essentially the dried blood of animals.

Apparently, it can help to raise nitrogen content in the soil, helping plants that otherwise might suffer from too little access to nitrogen.

However, too much can kill plants ("burns" them), and blood meal also raises the acidity of the soil. So I'd imagine that large amounts like regular rains of blood would probably kill most plant life over time—but, with the caveat that we're talking Earth plants. If your world has a different weather cycle that has existed for millions of years, then plants may well have evolved to take advantage of those differences. Even if this isn't something that has happened over millennia but is relatively new, say decades old, you might still see some plants do okay. I'm not really sure, just guessing here. But I did another Google search and found lists of plants that do better in a more-acidic soil. Frequency of the rains, and quantity each rain, would make a difference.

 

There is anecdotal evidence that the fields of northern France just after WW1 were more productive than before the war. There are lots of reasons for why this was so [if it was], but it has been put it down to the 1,000 of the dead in the ground.