So, catsclaw227, I invite you to fill in that "XXX" blank. What exactly do you want to do in terms of "managing your lands"?
Driving out enemies, collecting taxes, building structures, raising and equipping armies, aerial and naval operations, sieges, personalities of NPCs and your beloved "mechanical" factors for interactions with them -- those are all covered. You can appoint a steward/castellan to look after the logistics of keeping up your castle garrisoned, supplied and in good repair. You can hire sages, "the encyclopedias, computers, expert opinions and sort of demi-oracles of the milieu all rolled into one".
Agriculture, mining and (especially) trade are usually concerns beneath your station, apart from taxing them. It's not the sort of thing for which there was very much demand for rules in "adventure" games. However, if you really want to get into fodder, bushels, pigs and ducks ... the C&S Sourcebook (1978) says Fiat Lux! Yes, even the famously comprehensive C&S had initially glossed over matters "down on the farm".