Two brothers who lived on neighboring farms fell into conflict. It was the first serious one between them in forty years of farming side by side, sharing tools and trading labor without any trouble.
What does "trading labor" mean? Is it a fixed expression?
I wouldn't say it was a fixed expression. This is "trade" in the sense of "exchange". It appears to mean that they shared the workload of running the two farms. They regularly helped each other out.
not a teacher