|Measured data. 8' diameter, six bladed wind-turbine. Very optimistically called "3.5kW system". Average about 70 Watts at 10 mph wind. Link one Link two|
The devil is in the details. A 10 mph breeze is a respectable breeze and we usually don't get 50 hours in a typical summer week, at least not within a reasonable distance of the ground.
We might get significantly higher breezes when we have a storm system passing within 30 miles of our location. We get a lot of storms where we get wind but little rain.
My gut feel is that one, 8' diameter wind-turbine per 1000 square feet of garden/orchard would be a good starting point in my location.
One 8' turbine every 4000 square feet would provide enough supplemental water some weeks of the growing season but not all of them.