Irrigation-oil yield link studied in mint

Tam Moore
Freelance Writer

Capital Press

July 27, 2007

TULELAKE, Calif. - It's going to be busy late this month as harvest starts on a complex peppermint field. When scientists are done, they will have oil yield data for a variety of irrigation treatments on the reclaimed lakebed soils that dominate Klamath Basin mint-growing sites.

What makes the complex experiment possible - there are 24 different irrigation cutoff and harvest times in all - are a sophisticated sprinkler system and a miniature still purchased by growers through an Oregon State University research fund.

It took two years to establish the mint plot at the University of California Intermountain Research and Extension Center about one mile south of the Oregon border.

"Growers kept asking us, 'What time should we cut?'" said Harry Carlson, director of the UC station. "They said they don't really have a clue when the best time is to harvest ... and how soon to cut the water off prior to harvest."

The mini still, put in service two years ago, was calibrated during the 2006 mint harvest. Two boom sprinklers, just wide enough to cover a 20-foot-wide experimental plot, are deployed at the station. One is walked through the mint field; the other is part of a long-term experiment on irrigated pasture grass variety survival under water cutoffs.

Here's the setup for the 2007 experiment, with harvest cuttings on the earliest plots July 16, and on the last ones Aug. 20: For every harvest date, water is cut off three, 10, 17 and 24 days before cutting.

There are 96 plots, and each 20-by-40-foot plot will be hand harvested as July and August unfold.

It will be mid-winter before the massive data on oil yields and quality are ready for grower review.

Electronic soil probes are scattered around the plots, gathering data on soil moisture as the various irrigation schedules are followed.

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