Deficit irrigation evaluated

Alfalfa figures would provide numerical basis for water bank

Tam Moore
Freelance Writer

September 14, 2007

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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