It's unlikely that the Ferrars' wealth is from land.
If that is the case how come Mrs Ferrars settles a landed estate on Robert, when Edward disappoints her? And it is clearly only one of her properties.
“His mother explained to him her liberal designs, in case of his marrying Miss Morton; told him that she would settle on him the Norfolk estate, which, clear of land-tax, brings in a good thousand a-year;
She problaby would have divided her property fairly equally, between the 2 sons, when she died, but Edward angered her by refusing to give up Lucy, and she cut him out of her family and immediately made over an estate to Robert.