From
Wired:
The presence of shallow ground water has also brought land use change
to parts of the Sandhills. In the 1950s, center pivot irrigation
technology was developed and it allowed more acreage to be irrigated at a
much lower labor cost. Center pivots use moveable, elevated piping on
wheels that turn in a circle around irrigation wells and pumps. Water is
pumped directly from the ground and applied to crops as the swinging
arm passes over them.
Center pivot systems became much more used in the late 1960s and
early 1970s, especially after spikes in grain prices driven by large
purchases from the Soviet Union and other countries. For example,
Nebraska had 2,735 of these systems in 1972 and by 1975 the number of
center pivot irrigation systems had more than tripled to 8,517.
Peripheral areas of the Sandhills that had more level lands, shallow
depth to water and somewhat less erosive soils became areas of potential
land use conversion. In an Aug. 17, 1972, Landsat image, a
discontinuous area of the Sandhills south of North Platte, Nebraska
shows up as mostly shades of gray and green in this false color 4-2-1
band combination. The summer-dried grasslands in the center of the
subset show little actively growing vegetation. Crop fields, mostly on
the edge of the 1972 image, show up primarily as geometrical shapes of
bright white (harvested, mostly bare soil reflecting back) and red
(actively growing vegetation). Few circular features designating center
pivot irrigation systems appear.
The situation had changed by the time of this Aug. 22, 2011, Landsat
image that shows substantial gains in center pivot deployment across
this portion of the Sandhills. The bright red circular fields, most
likely growing crops such as corn and alfalfa hay, stand out
interspersed among the mute grays of the native grasslands.
That is amazing. The Sand Hills have more water resources than Western Kansas. Out near Garden City, I would expect that in 40 years you'll see much less center pivot irrigation.
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