- Author: Ben Faber
Recently I was asked why an irrigation schedule could be projected for almond and citrus in the Central Valley (Almonds:http://cekern.ucanr.edu/Irrigation_Management/Almond_Drip_-_Microsprinkler_-
_Flood_Weekly_ET/Citrus: http://cekern.ucanr.edu/Irrigation_Management/Citrus_ET_by_age/ ) and why the same couldn't be done for the main avocado growing areas. Here was my response:
Generating a generic irrigation schedule for avocados along the coast is very difficult and if done would be terribly misleading. Scheduling gets really hairy along the coast where avocados are grown. As you get further from the coast the water demand (ETo) increases in many months, typically increasing in the summer. This can be most pronounced in the late winter/spring when the fog along the coast really causes a contrast between coastal and inland conditions. May in Ventura, the sun comes out for about 2 hours and in Fillmore 20 miles inland it may be 90 F at 4 PM. The fog is a major determinant for irrigation demand and it varies daily, monthly and year to year from Monterey to San Diego. So fog can throw off an irrigation schedule.
The next variable to area-wide scheduling is the topography where avocados are grown, usually slopes to improve air and water drainage. Depending on the aspect and slope position, the ETo can vary tremendously depending on the sky conditions and what those conditions are depending on the time of day (such as foggy in the morning and clear in the afternoon). So west and south facing will always be higher than north and east. The top of the slope that intercepts more wind than the bottom and will have higher ETo than the bottom of the slope. And if the trees intercept more evaporative conditions midday when the sun comes out, it will be much higher than the east side in the morning when fog is dripping off the trees (zero evaporative demand). Then as you go south from Monterey to San Diego the ETo goes up, just because of latitude and sun interception. These conditions are very different from Fresno where ETo in July is 0.6 inches per day and is the same until Sept, the sky is clear most days and trees are grown on fairly flat ground.
Now throw in rainfall. Almonds are deciduous and only count on the value of rainfall as that which is stored in the rooting zone going into spring when leaves are come out. Avocados rely on winter rain for transpiration and salt leaching. In a good year a significant portion of the total yearly ETcrop can be subtracted from the irrigation demand. In a low/no rainfall year that all needs to be made up by supplemental irrigation.
An almond grower in the Valley might be able to go onto a calendar, set the clock if they have water on demand and walk away. That's never going to happen in a coastal avocado orchard. Depending on where the avocado is grown and the ETo at that site, applied water might vary from 1.5 ac-ft per acre to 3.5. This will depend on rainfall (when and how much), water quality (which determines leaching requirement) and the system delivery (system efficiency). This system issue can be further complicated by whether the delivery is on-demand or whether a certain amount will be delivered at a certain date for a certain length of time - 24 hours or 48. This makes it difficult for the grower to put on exactly what ETo and other issues the trees would demand. In this case, the delivery system determines the schedule.
So this is why there's no chart showing ET demand for coastal avocados where the bulk are grown in California.
A CIMIS (CA Irrigation Management Information System) DWR weather station for calculating crop water requirement.
- Author: Ben Faber
By way of the San Francisco Chronicle
Hopes of an almighty El Niño bringing rain to a drought-stricken California - with its fallow fields, depleted streams and parched lawns - were further dashed Thursday. The National Weather Service, in its monthly El Niño report, again downgraded the chances of the influential weather pattern occurring in the fall or winter.
The odds were 80 percent in May, but were placed between 60 and 65 percent this week.
Meanwhile, the agency also announced that the much-needed weather event is likely to be weak instead of moderate in strength - another retreat from the more robust projections made earlier this year that fueled speculation that California's three-year dry spell might be snapped.
- Author: Ben Faber
California Drought Watch
Although water is in short supply, UC Davis' expertise in water-related issues is not. California Drought Watch brings together the university's globally renowned resources in water sciences, management, law and agriculture to ensure that policymakers and the general public have access to the knowledge, research and technologies that are crucial to addressing the challenge of the state's drought.
Visitors to the site will find the latest drought research and news headlines, as well as drought management tools from UC Davis experts and water organizations throughout the state. They will discover how UC Davis is cutting back on water consumption, learn about upcoming events like the April 25 Drought Summit, and find out how to reach UC Davis' top experts in drought and water management.
“Policymakers and the public need to see, not just be told, that UC Davis is a go-to place on drought,” said Jay Lund, director of the UC Davis Center for Watershed Sciences. “This site should help draw tighter the wide range of work done on drought and related subjects from all across the campus.”
Visit California Drought Watch.
Farmer and Rancher Voices from the Drought
Over the sound of bleating sheep and singing birds, Dan Macon describes how the current drought has affected his sheep ranch, Flying Mule Farm, in the Sierra Nevada foothills: “This is the driest of three dry years in a row for us … Over the last three years, we've reduced the size of our flock by half. Because we've reduced the size of our flock, I have taken a part-time job and will probably take a second part-time job this spring.”
His is one of several audio stories compiled as part of Farmer and Rancher Voices from the Drought.
A team of UC researchers began the project this spring. Led by Ken Tate, UC Davis professor of plant sciences and rangeland watershed specialist in Cooperative Extension, they use digital tools to capture the voices of farming and ranching families who are battling the worst drought of their careers.
Each week, the team posts new tracks to SoundCloud — an audio-streaming service and social network where users can upload, record and share tracks they create. Friends, loved ones and colleagues of ranchers and farmers are also invited to interview them and post tracks to the SoundCloud group page. Several of the farmers and ranchers share practices that have worked for them so that others struggling with the drought can better cope.
Members of the state's farming and ranching community also share stories, photos and comments at the project's Facebook group page.
The project was inspired by Caroline Henderson's “Letters from the Dust Bowl,” which documented the voices of farmers and ranchers leaving dust-covered Oklahoma in the 1930s in search of a better life in California.
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