Probably just a terminology difference. Ahay and I are from the same area.  In the 1940 to 1960 time frame nearly every acre was developed for gravity/furrow irrigation.  When pivots came acres started changing to pivot irrigation but many of those acres remained as ridge till or conventional till with a ridge/row cultivator pass in the summer for weed control AND to make the fall tillage pass easier.  There is still some pipe/furrow irrigation around, especially closer to the Platte River an in the Central Nebraska NRD area but our Upper Big Blue NRD is threatening water pumping restrictions and furrow irrigation uses lots more water.  For the most part it is only on really odd shaped fields and pivot corners.  80% of my acres are planted onto ridges that are 6-8 years old and the other 20% is no till for erosion control purposes.  95% of my acres are under pivot irrigation.  The ridges are helpful because planting time is usually our wet time (not this year!) and the ridges help keep the seedlings in better soil conditions.