Geography Reference
In-Depth Information
irrigation. And if worse comes to worse, well, portions of the High Plains could revert to something
akin to the lush natural grazing lands (the prairies) that were done away with to make way for farms.
Applied Geography: Drip irrigation
In arid and semi-arid lands, water for irrigation has long been applied to fields by means
of open-air ditches between rows of crops. Although this method has helped satisfy the
food needs of unknown numbers of people over the millennia, it has three significant
drawbacks. First, a substantial volume of water may evaporate before it reaches the
plants. Second, the amount of water that seeps into the soil is usually far more than the
plants actually need. Third, the mineral salts that build up in the soil as a consequence
of evaporation may ultimately undermine the usefulness of the farmland and lead to its
abandonment.
In some countries, however, these environ-mental effects have been largely nullified by
introduction of drip irrigation. In this technique, water reaches the fields and is distributed
up and down crop rows by means of thin plastic tubing that is perforated by tiny holes
every few inches. Water is forced through the tubing at very low pressure; so instead of
squirting out of the holes like so many tiny fountains, the water slowly drips out. Because
of the tubing, very little water is lost to evaporation. Moreover, drop by drop application
results in little water wasted and minimal salt accumulation. All in all, therefore, drip irrig-
ation is proving to be an effective and fairly low cost means of making maximum use of a
scarce arid-land resource.
Good to the very last drop
The bottom line with respect to run-off and infiltration is that you can't take more water out of
the system than nature puts into it. Reservoirs and aquifers
can
dry up. In that event, water will
still be everywhere, albeit in forms that are not readily accessible (such as vapor in the air or
veneer surrounding soil particles) or in amounts that satisfy local needs. Humans number six
billion and counting. More people mean more direct consumption, more irrigation, and more
industrial use. How these needs will be met remains to be seen, but they will clearly reflect the
geography of a precious resource.
