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A
farmer turns alfalfa under conventional irrigation
management at Whipple Ranch in Northern California. |
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Deficit irrigation evaluated
Alfalfa
figures would provide numerical basis for water bank
Tam
Moore, Capital Press 9/14/07
ETNA,
Calif. - The Scott River, a major tributary of the Klamath
River of Northern California and Southern Oregon, has shrunk
into pools and hidden itself beneath gravel in this dry
September, blocking the way upstream for any migrating salmon.
But if research being carried out next to the Scott at Keith
Whipple's ranch and elsewhere in Northern California is a
success, there may be a way to calculate the value of a farmer
intentionally drying up a perennial crop to allow water to
reach the river in time of drought. Local ranchers have
already formed a water trust that could administer such
cutoffs, but there's wide debate about the value of water
saved - even the amount of water actually saved.
Those elusive figures, which would provide the basis for a
water bank system, are the aim of Steve Orloff, a University
of California farm advisor in Siskiyou County. Orloff is an
agronomist and researcher specializing in alfalfa.
The project is time-consuming, based on field trials carried
out from 2003 through 2005 in Scott Valley, the Klamath Basin
and the Sacramento Valley. Data gathered this year and next
will sharpen the calculations.
What's going on at a commercial scale on the Whipple Ranch is
an extension of the trials that established the deep-rooted
alfalfa plant's ability to survive on far less than the water
used to produce optimal, season-long cuttings of high-quality
hay. They also showed alfalfa subject to a water cutoff in one
season has the ability to recover production the next season.
As Orloff led the 58th annual Siskiyou Cattle Tour through
Whipple Ranch in late August, the crew raked a heavy third
cutting off a conventionally irrigated field, and a
center-pivot walked more water on another conventional field
that's part of the test.
But down by the Scott, where there hasn't been any water since
June 1, the alfalfa has either slowed to a standstill or dried
up, depending on what's beneath the field. Ranch manager
Gareth Plank said the dried-up spots represent places with
thin soil atop river cobbles.
California has about 1 million acres of commercial alfalfa, so
saving from 11 to 23 inches of irrigation water per acre in
dry years could put a lot of water back into streams. Orloff
hopes to quantify the actual amount of water saved by
calculating relationships between the evapotranspiration rate
of the plant, the moisture in the soil and any input from
occasional summer showers.
There's already data on how saving water impacts hay yields -
in locations such as Scott Valley that can cost up to 2.2 tons
per acre over the season.
In parts of the Klamath Basin where there's either a high
water table or a near-surface perched soil water supply, the
UC researchers have found that calculations are much different
from more-typical hay production sites.
Preliminary work, adjusted for hay prices in the 2003 through
2005 growing seasons, show farmers in the valleys of far
Northern California would need to get at least $119 per acre
foot of water to replace income lost by water savings. The
actual value on a particular site ranged from $49 to $240 an
acre foot.
But in the longer Sacramento Valley growing season, depending
on the site and hay prices, a saved acre foot of water might
be worth from $96.9 to $200 an acre foot.
Freelance writer Tam Moore is based in Medford, Ore. E-mail:
moore.tam@gmail.com.
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