A combination of Single Payment, sheep farming and liveries is the short answer
The long answer is waay too long
It all very much depends how much land you have, how much money you need to earn and what sort of skill set you have.
Um ok need to pay back on a buisness loan . horses/ponies would bring in some pennies but need something else but quick turn around but dont want to lose grazing so unless i have 100 geese every 14 weeks turn around for (meat)
Car boot sale?
Clay pigeon shoot?
Caravan site?
Hold horse shows/dressage, etc. and pocket the profits - if any.
Fence an area securely and let it out for dog training.
The trouble with a lot of options like above is you can be so restricted by what the planning bods will allow, they may be your first port of call as there may be restrictions on what business you can start.
Unless you already know lots about farming what about just renting it out in one lot? Might not make as much but is usually at least a guaranteed amount.