In Roll of Thunder, Hear My Cry, it's all about the land. Families like the Averys and the Turners are at the mercy of their landowners for economic prosperity (or, economic failure, more like it). But the Logans have land, so they get to exercise independence that the others can't. As the novel progresses and their land is threatened by Mr. Granger, this issue becomes more pressing. Why does Papa obsess so much about keeping their land? Simple. Consider the legacy of slavery. The Logans descend from slaves, who were forced to work somebody else's land. Now, they own the land, but the threat of losing it is never far away. That's why Cassie also cries for the land at the end of the book.
For the Logans, land is inseparably linked to the concept of "family."
For Mr. Granger, land is something you dominate, and use as a force of domination over others.