There's a double meaning in the title of this post. The usual meaning is farmers whose income is low, low compared to other farmers in the area or nation, low compared to what's needed for a good life in the nation, low compared to someone else. See this Treehugger/Oxfam post.
But the other meaning is farmers who farm poorly, poorly because their land is poor, poorly because they're far away from markets, poorly because they lack the knowledge, the social capital, others have. Many would like to believe in the Lake Woebegone corollary, that all farmers are above average. I regret to inform you that's not true; whichever nation or locality we're talking about, some farmers are good and some aren't. Some land is good, some isn't. Some land is on the railroad, some isn't. Some farmers have learned from experience what works, some are stuck in a rut. Some farmers are open to new ideas and techniques, some are waiting to die.