I'm interested in the following information, and will be happy to follow any leads to good resources for the info:
How were they cut?
Were they irrigated?
Did they fertilize?
Did they overseed?
Are there things they did then that can inform how to maintain healthy turf today without the use of synthetics?
It boils down to sheep, cattle and manual labour.
This website gives a good introduction and some links to "estate keeping" in Great Britain at Jane Austen's time. Let me extract the major points:
First, you need to distinguish between the larger fields / meadows further away from the house and the adjacent grounds.
Lawn care (or, perhaps "meadow care") relied much on sheep and cows and sometimes deer who would keep the grass short by grazing and fertilize at the same time. As visible fences were considered "ugly" - the goal was to create a "natural" landscape even though sometimes major changes were made like transplanting mature trees or creating artificial lakes - a ha-ha kept animals from freely wandering onto the lawns near the house. Assume that these meadows appeared less evenly than if mowed by a tractor, but that's not crucial if viewed from a distance. To even out, they could be mowed down manually with a scythe. This required many labourors.
The grounds closer to the house could be "mowed by sheep or cows", too. Remember that the owners would not necessarily be in residence all the time. Assume that most of the droppings would be removed by the gardeners. But mainly the upkeep was done by hand (scythe), the source claims cutting once a week in the morning and flattening the grass with a heavy roller would ensure an even, short lawn that even the ladies with their dainty shoes could comfortably use.
As for watering, I'm quite sure that the gardeners would rely on the wet English summers...
Here's another link that might be of interest:
https://www.planetnatural.com/organic-lawn-care-101/history/
Basically, as already said, sheep were used, but from the 17th century onwards in Britain, wealthy landowners needed huge teams of gardeners to keep the lawns and grounds good looking. Grass was cut by teams using scythes, and hand weeded - scarification and aeration were all done by hand, and besoms were used to remove worm casts and to brush top dressing (a mix of peat or garden compost, loam and sand, in varying ratios according to the soil type, applied in autumn) into the holes made by the aeration, and also lightly spread across the grass and to fill in hollows and dips. It was not unusual for a grand estate to have one or two head gardeners, with up to 10 or 20 undergardeners, some of whom were employed only at certain times of year, with a nucleus of around 8-10 on the permanent staff. Truly, a well kept lawn and garden in those days was evidence of great wealth.
Top dressing is still done on sports turf by groundsmen today - only a few gardeners with lawns bother with this now, but it is highly effective.
