Wouldn't the type of grasses grown have to be figured into the equation? Whether the grasses are native, or planted would make a difference. Ours is nearly all native grasses, and many varieties of that.

Here, we get 15 inches of total precipitation, with the majority of it USUALLY coming during the growing season. It seems the timing of the moisture would also have a high involvement.

Then the soil types. Ours is gumbo, for the most part. It holds water pretty well, and water penetrates quite deeply.

Terrain would matter, it seems to me. We figure about 20 to 25 acres, and sure do adjust during a drought to protect those native grass pastures.

mrj