Satellites and maps

I've been slowly looking over the satellite view of our planned route. It's really funny what it can show you about farming in Texas. When you come into the Panhandle most of the plots are those odd squares with a circle of land cultivated in the middle. I actually called my nieces in to look a the picture and we located a city in the middle to be sure we're paying attention to figure out what in the world they're doing to make all those perfect circles. Almost exactly when you hit Lubbock the farmers start cultivating the soil on contour. Between Lubbock and Sweetwater nearly every field is farmed and every farm follows the contour. I wonder what caused the change and why it's so geographically defined? Also, did they go from contour to circles, circles to countour, or what?

Those circles are center-pivot irrigation fields.    http://www.kuriositas.com/2014/12/center-pivot-irrigation-real-crop.html

I thought it was something like that. I'm trying to encourage the girls to be looking and thinking about what they see on this trip.

We're probably going to spend a total of more than three full days in the car over the next week. Part of the reason my family does so well on road trips is that we are engaged in the landscapes we travel. I want them asking questions and making up stories about what they see. It's probably equivalent to the road games I've heard of other families using.

I'm more curious about what made the difference between the farms on one side of Lubbock plowing on contour and the other side all doing the circles. Assuming we have daylight when we pass the contour plowed fields, I'm definitely going to be discussing the whys and wherefores of following contours with the girls.

I looked at the satellite image and yeah, it's really interesting!  My guess is the contour areas are older farms - in our area old cotton farms have those plowed contours.  

I'm more curious about what made the difference between the farms on one side of Lubbock plowing on contour and the other side all doing the circles.

I'm guessing one of two things:
It could be where 'bottom land' meets hill country.
Or it could be new crops have different irrigation needs than previous crops did.

I am taking notes on different theories to see if personal observation will confirm or deny. Something that supports the idea that contour plowing is the older technique is that there are many areas which have what appear to be less defined contour lines, as if the old fields have been weathered down over time. Most of those aren't right on the road, so I don't know if we'll pass close enough to get good observations.

The center-pivot irrigation systems are much more of a modern concept than the plowing on contour.
I suspect that these circles are much newer than the old contour lines.

Those circles are much more prevalent now than they were a few years ago.