What on Earth are the Circular plots on the Sat?
More precisely: Central Pivot Irrigation. A central pump with an irrigation gantry that rotates around it.
Could be any crop. Cassine obviously knows the area well enough to know the crop.
The green ones are active, the brown ones possibly recently active and the clear ones fallow.
If it is as Cassine says potatoes, then a four-five year fallow period is needed to eliminate infestations of Nematodes. It is usually more economical to move the central pivot than to try another crop on the same pivot. in some areas of the western Cape a single crop is all that is possible and Dept of Agriculture has requested assistance on restoring the old circles to natural Fynbos (which is done properly would cost about 5-10 the value of the potatoes harvested).