If a Westeros noble's wealth depends on agriculture, how much does he know about agriculture? Can Mace Tyrell sow and harvest a wheat crop?
A noble doesn’t need to know how to sow and harvest a wheat crop and wouldn’t ever learn - indeed, it would be injurious to the dignity of a nobleman to suggest that they should undertake the work of a smallfolk.
However, depending on the nobleman, they might well learn from their maester a good deal about agriculture from a managerial standpoint - what kind of land is best suited for what crops or livestock, how best to rotate crops to maximize yield, the theory of livestock breeding, the uses and siting of various agricultural improvements, etc. - so that the various manors and lands of their fiefdoms are run well. On the other hand, it may be considered that this too is the province of lesser men - bailiffs, stewards, reeves, maesters, etc. - and that all a nobleman needs to know is the old Parthian curriculum.
And that would largely come down to the ideology of the house. Randyll Tarly clearly leans to the latter view, whereas I would be willing to bet a substantial amount of dragons that, while no Redwyne earns their living by stomping grapes or cutting weeds, they pride themselves on being really, really obnoxious oenophiles.
You probably know Neil deGrasse Tyson as an astrophysicist with a seemingly endless stream of science fun facts at his command. You might not be aware that he is also a great oenophile and lover of food.
Some 16 years ago, before I was a journalist and illustrator, I worked with Neil at the American Museum of Natural History. He would sometimes carry around a small canvas tote bag. As I recall, the bag would contain one of two things: either a weighty, mango-sized meteorite to show to guests of the museum, or a bottle of wine to gift to a colleague.
It was pretty symbolic of his twin passions – the heavens, and wine. (By extension, that includes cuisine.) I recently talked with NdGT about how these all collide in the kitchen.