We've been irrigating in hot, dry, windy weather for a long time, and you won't find sprinklers on top of the pipe here. I'm concerned about evaporation with that kind of setup, but I think the bigger problem actually becomes drift. The water turns into a fine mist and gets thrown so far that it never soaks very deep into the soil. Every drop that doesn't land where it's needed is a drop wasted. Last year taught us a lot about efficiency, since it didn't rain at all. Any crop that was raised was done on irrigation alone. Case in point:

This pivot is equipped with iWobs on 10 feet spacing, 5 feet above the ground. At the time the system was nozzled for 550gpm. Notice those stripes across the field. That's where a drop got blown over a truss rod earlier in the season. The way iWobs throw the water, that one drop sitting higher and farther away from its neighbors disrupted the pattern enough to cause a noticiable drop in applicaiton efficiency, resulting in early stunting of the corn under it. The water just didn't soak deep enough. Unfortunately, it took me a while to put 2 and 2 together, and by the time I got the drops flipped back over the damage had been done.

I was holding the camera at eye-level here (I'm 5'11"). These short strips yielded nearly nothing, the field average was 70.

I don't mean to rag on anyone for using iWobs; this was just the easiest way I could find to demonstrate the importance to getting the water you pump to where the roots can reach it. Most pivots here are equipped with Senninger LDNs or Nelson D3000s, with 6psi regulators (10psi for bigger wells). We've all tried putting the nozzles at different heights above the ground, but I think 18-24in works the best. On some of our smaller wells we're experiementing with bubbler pads, or just turning the splash pad upside down for the same effect. We're trying to get the water to the ground with as little drift and evaporation as possible. So far I think the results are very encouraging.