Irrigated Acres Up, Water Application Rate Trending
Down
Noel
Gollehon
Why do farmers irrigate? The benefits of
irrigation include higher yields with increased
drought protection, more cropping alternatives,
reduced frost damage, higher quality products, and
increased income stability. Nationally, irrigated
corn yields are 30 percent greater than nonirrigated
corn. Yield increases average over 60 percent for
other field crops, yet the most valued contribution
of irrigation is its use on vegetables, orchards,
and horticultural crops.
In 2002, U.S. irrigated farmland
occupied 55.3 million acres, down 1 million acres
from 1997. In recent years, national irrigated area
has stabilized at about 55 million acres as continuing
growth in Eastern States has been offset by declines
in Western States. Variations within the decades-long
trend of increasing irrigated acres can largely
be explained by year-to-year changes in four factors:
farm program requirements, crop prices, water supplies
in the West, and weather influences on the need
for supplementary irrigation in humid areas. In
general, there is an increasing reliance on irrigation
in the humid East, with large concentrations of
irrigation emerging in Florida, Georgia, and, especially,
the Mississippi Delta, primarily Arkansas and Mississippi.
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Changes in total water withdrawals
for irrigation reflect per acre efficiency gains,
shifts in crop locations, and changes in acres irrigated.
Averaged over all States and crops, the average
water application rate has declined by over 5 inches
(about 20 percent) since 1969, to levels below 20
inches per acre in 2003. Producers have adopted
more water-conserving practices and shifted production
of some commodities to more humid and cooler areas,
requiring less supplementary water. Irrigation application
rates can vary from less than 6 inches per acre
(sorghum in the North-Central States) to more than
4.5 feet per acre (orchards in the Mountain States).
Per acre declines in application rates have partially
offset the need for water to supply the increase
in irrigated acreage. Over the 1969-2003 period,
irrigated acreage increased by over 40 percent while
total water applied increased by only 11 percent.
Irrigated agriculture is likely
to remain important both as a demand on water resources
and as a land cultivation practice. However, continued
changes in the irrigation sector are anticipated
in response to increasing water demands for urban
and environmental uses, as well as evolving institutions
governing farm programs and water allocations. Water
withdrawals for agricultural production will likely
continue to decline, with at least some portion
shifted to satisfy alternative goals.
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