Blake Sanden, a University of California advisor for almond and pistachio growers since the 1990s, officially retired as of June (for more on Blake’s career achievements, see this blog on the UC site).
But if you talk to Sanden, you can hear the same passion as ever for research projects that inform California growers.
Sanden talked with Ceres Imaging about his career working with tree nut growers, including a recent multi-year trial he performed that shows a strong correlation between Ceres aerial images and applied water in almond orchards.
Q. Congratulations on your retirement–when does it start?
Blake: The formal separation date is June 28th, but that is nowhere by any means the end of the current projects to which I am committed. Certainly through the end of this year I will continue to work on the Pistachio ET by salinity project...to come up with revised pistachio crop coefficient values.
It doesn’t mean I’m disappearing. I already have two emeritus commitments to other UC projects.
Q. How does the landscape for today’s tree nut growers differ from when you started in the field in the late 80s?
Blake: It was 30 years ago this last February I started working for Paramount.
Because of the yield and price of almonds, people who were growing three or three and a half bales of cotton per acre were making more (than almond growers).
Now almonds are king, for the valley acreage out there.When I first got around almonds in the late ‘80s, the average yield in California I believe was around 1,380 pounds per acre.
Most of the almonds were still flood-irrigated, and a lot of the more advanced growers had installed solid set sprinklers, starting about 15 or 20 years earlier. Implementation of micro irrigation on almonds had just begun. In the mid-to-late 80s, you had enough people at the starting point with microirrigation, all of a sudden you had people regularly getting 1,800 - 2,000 pound yields. You had an expansion in acreage, a change in the marketing from the Almond Board.
In the late 80s, I’m going to say that maybe 30,000 acres of almonds in California were irrigated with drip or microsprinklers.
Q. How is work going on the almond applied water study that found a correlation with Ceres imagery?
Blake: 2017 was the last year. We buttoned that up. The combined 2016-2017 data is the most complete set we have (for flow meter to applied water).
The final analysis of average yield–as a function of our irrigation treatments and as a function of the average Ceres conductance–very, very much lines up with that 2016-2017 data.
Q. One of your final projects examines salinity levels and pistachio trees. Can you talk about that work?
Blake: This survey pretty much does represent the soil variability that could be encountered in our California pistachio plantings. It does not represent all the climatic variability.
Areas varied from typical low salinity sandy loam soils on the east side of the San Joaquin Valley originating from the Sierra Mountains, going over to the west side of the San Joaquin Valley where saline, clay loam fields originated from alluvial sediments off the Coastal Range hills.
In general I would say the areas are a good cross-section of the pistachio acreage out there.
(The work used) an EM38 ground magnetic conductivity meter. It costs $19,000 or $20,000 but you can use it forever, there’s nothing that wears out. Once you’ve got it, the only real investment involved is the time of the guy out in the field.
Q. How did Ceres imagery help with the salinity study?
Blake: As salt goes up, vigor and tree size goes down. And Ceres images picked that up wonderfully.
That conductance algorithm you guys are using, it really is a high-quality interpretation of canopy temperature. There’s other people doing canopy temperature but..there’s something about the way you have parsed the pixels and worked on the elimination of the dirt that shows you’re on the right track.
Now you have a tool that tells you where to go back and do some more intensive sampling. You need to go in and do some extra acid or sulfur work in there...maybe put an extra foot of water in those tough spots over the winter.
That’s where what you guys are doing can be really handy to help a grower make some very real corrections in a field.
Q. What are the main takeaways from your pistachio salinity work?
Blake: As an ironclad rule of thumb, the old salt tolerance threshold of 9.4 decisiemens that we came out with back in 2002 is incorrect.
You absolutely do start losing yield before that, somewhere around an EC of 5 or 6.
We’ve got a much better measure between magnetic conductance and yield than just salinity.
It brings us back to the reality that we can not just accept one single standard for every field that’s out there.
With that realization, do we have better tools of making an assessment of how bad or good any individual field will be?
Here’s a link to Blake Sanden’s Soil Salinity & Leaching Excel Calculator for growers.