Something these researchers/writers dodge is that if you tried to grow similar crops in the Orkney Islands today, with or without nitrogen fertilizer, you would have a problem. It’s too cold.
The Gulf Stream is the moderating influence on that part of the world; palm trees survive in the inner hebrides. But it doesn’t get hot, or even warm (if ya ask me) in the Orkneys. You’re going to enjoy a lot of colder bean crops, asparagus, short-season varieties of other things, fish, and meat.
http://www.orkneyjar.com/orkney/climate.htm
OTOH, they still have this:
https://en.wikipedia.org/wiki/Twatt,_Orkney
So does the Shetlands, where the sign is funnier:
https://en.wikipedia.org/wiki/Twatt,_Shetland