On my first job out of school, I was told to design an instruction decoder for a microprocessor. It was a complex block for the early 80s, taking all of 30,000 transistors, and it occupied one whole corner of the chip. When people asked what I did, I would say “You see these little shiny squares in the upper corner of this fingernail-sized chip? That’s mine.” Not impressive.
But just today I read the obituary of Robert Daugherty, founder of Valmont Industries, which pioneered center pivot irrigation. Here’s what his handiwork looks like:
Kansas, June 2001, from the ASTER satellite. Green circles are corn, yellow wheat. Small circles are 800 m in diameter, large 1600 m.
Here’s some more info on this picture from NASA. In the center pivot scheme, a 400 m long pipe sweeps out a slow circle around a field, dripping water as it goes. The pipe is supported by towers, each of which has an electric motor to drive it:
Pivot irrigation on cottom
Each tower has angle sensors to keep the segments all in line. The water comes from a well in the middle.
In the early 50s he bought the design from one Frank Zybach. His people improved it and marketed it all over the world. Now 42% of all irrigation in the US is done this way. How can you tell? Because, as the first picture shows, you can count these circles from space.
Center pivot irrigation replaces the traditional technique of flooding ditches with water. It uses much less, because less is lost to evaporation. Fields can get a regular drip instead of a one-time flood. It also uses much less labor (no need to go around pulling up ditch sluice gates) and works on fields that aren’t flat.
Daugherty just died at age 88 in Omaha, leaving 3 sons and 9 grandchildren. He put most of his fortune into the Daugherty Foundation, whose largest grant appears to be $50M to the University of Nebraska to study water issues in agriculture. Those are crucial in all the western states, and will be crucial everywhere in the not distant future.
There’s an old line – “Real engineering is where if you fall off of it, you die.” Daugherty could go one better – “Real engineering can be seen from space!” There’s a boast few can make!
A Niche in the Library of Babel 
Why are they on a square grid? A hexagonal packing would be much more land efficient.
Or overlapping circles, with individually controlled spray nozzles that only irrigate the corners, and shut off over portions of the field that already have been watered.
I must be missing something, here, since these are incredibly obvious “innovations” that struck me after two minute’s thought.
re: hex packing – Good question! Farms tend to be rectangular, so it might be a matter of a square arrangement fitting better into a rectangle than a hexagonal one. If you had an NxN array of circles of diameter 1, a square packing would have an area of N^2 (and a coverage of pi/4 = 79%) while a hex packing would have an area of:
(N + 0.5) * ((N-1) * sqrt(3)/2 + 1)
The hex is denser for N >= 5. If the circles are 1/2 mile in diameter (as these are), then the farm is >= 2.5 miles on a side, or 4000 acres, which is pretty big. I see that only 9% of farms in Kansas are bigger than 2000 acres.
A hex packing also wouldn’t let you have straight roads across the farm.
re: why not overlap circles? – Also good! Some possibilities:
– If they overlap, the sprinklers can crash into each other. I see that a company named Isaacs makes wireless switches to prevent exactly this. Each pivot signals the others when it’s in a certain angular range, and the others wait until it leaves. It could be that when this picture was taken in 2001 it wasn’t economical to run wires from one pivot to the next to control this. It may be now, though.
– Putting controls and valves on individual sections of the sprinkler may not have been economical, although that’s probably changed.
– Turning off one section of the sprinkler changes the pressure on all the others, which affects the water distribution along the pipe. Probably also controllable, and easier now than it used to be.
So it probably is possible to overlap the circles with current electronics, but may not have been earlier.
One other thing I should have mentioned in the post – people in the Midwest are deathly worried about exhausting the Ogallala Aquifer, an Ice Age remnant that supplies most of the wells for these systems. Water levels are dropping all over region because of over-pumping. Center-pivot can help, though, because it makes far more efficient use of water than other schemes. Over the next century, though, dramatically less water will be available here.