- Author: Ben Faber
These are hard days for navel oranges. Drought stress. Salt stress due to drought. Then a heat wave in July that messed the trees up. And now we head into a weird fall with maybe rain. Maybe no rain. Maybe a little rain. This is ripe for navel splitting. This time of year when they are starting to build sugar, they are also ripe for splitting.
Years of drought, and a stressed tree are a perfect set up for navel oranges and fruit splitting.
The days have turned cooler and suddenly out of nowhere there is rain. That wonderful stuff comes down and all seems right with the world, but then you notice the navel fruit are splitting. Rats! No, a dehydrated fruit that has taken on more water than its skin can take in and the fruit splits. This is called an abiotic disease. Not really a disease but a problem brought on by environmental conditions.
Fruit splitting is a long-standing problem in most areas where navel oranges are grown. In some years, the number of split fruit is high; in other years it is low. Splitting in navel oranges usually occurs on green fruit between September and November. In some years, splitting may also occur in Valencia oranges but it is less of a problem than in navel oranges.
Several factors contribute to fruit splitting. Studies indicate that changes in weather including temperature, relative humidity and wind may have more effect on fruit splitting than anything else. The amount of water in a citrus tree changes due to weather conditions and this causes the fruit to shrink and swell as water is lost or gained. If the water content changes too much or too rapidly the rind may split. In navel oranges the split usually occurs near the navel, which is a weak point in the rind.
Proper irrigation and other cultural practices can help reduce fruit splitting. Maintaining adequate but not excessive soil moisture is very important. A large area of soil around a tree should be watered since roots normally grow somewhat beyond the edge of the canopy. Wet the soil to a depth of at least 2 feet then allow it to become somewhat dry in the top few inches before irrigating again. Applying a layer of coarse organic mulch under a tree beginning at least a foot from the trunk can help conserve soil moisture and encourage feeder roots to grow closer to the surface.
If trees are fertilized, apply the correct amount of plant food and water thoroughly after it is applied. If the soil is dry, first irrigate, then apply fertilizer and irrigate again.
- Author: Ben Faber
Here's a pretty technical report of water efficiency in avocado - the amount of water it takes to make fruit. It looks like there might be some varieties that could produce more fruit with less water. It's a promising start to selecting a tree that could produce under the increasing drought conditions found in avocado growing areas.
Evaluation of leaf carbon isotopes and functional traits in avocado reveals water-use efficient cultivars
Plant water-use efficiency (WUE) describes the ratio of carbon gain to water loss during photosynthesis. It has been shown that WUE varies among crop genotypes, and crops with high WUE can increase agricultural production in the face of finite water supply. We used measures of leaf carbon isotopic composition to compare WUE among 24 cultivars of Persea americana Mill (avocado) to determine genotypic variability in WUE, identify potentially efficient cultivars, and to better understand how breeding for yield and fruit quality has affected WUE. To validate carbon isotope measurements, we also measured leaf photosynthetic gas exchange of water and carbon, and leaf and stem functional traits of cultivars with the highest and lowest carbon isotope composition to quantify actual WUE ranges during photosynthesis. Our results indicate large variation in WUE among cultivars and coordination among functional traits that structure trade-offs in water loss and carbon gain. Identifying cultivars of subtropical tree crops that are efficient in terms of water use is critical for maintaining a high level of food production under limited water supply. Plant functional traits, including carbon isotopes, appear to be an effective tool for identifying species or genotypes with particular carbon and water economies in managed ecosystems.
Read the article:
https://www.sciencedirect.com/science/article/pii/S0167880918301828
- Author: Ben Faber
The Irrigation Training & Research Center (ITRC) of Cal Poly San Luis Obispo tested 28 different pressure-compensating models of microirrigation emitting devices from a total of nine manufacturers in order to compare independent laboratory testing with manufacturer specifications.
The test results indicate that:
The majority of ~0.5 gallon-per-hour emitters (drippers), regardless of manufacturer exhibited:
-
Good uniformity of manufacturer
-
Had excellent response to pressure variation
-
Had consistent flow rates within the nominal operating pressure range
But that the percentage of well-performing products decreased as the designed flow rate increased. Many of the emitters designated as microsprinklers or sprayers, although pressure compensating did not compensate at the normal operating pressures. Often the pressure compensating feature did not start performing until much higher pressures were achieved. Often this occurred when clogging occurred and this clogging often occurred where the pressure diaphragm was located and was not performing. Sediment would get in back of the diaphragm. Effectively the emitters were not pressure compensating. The testing procedure of numerous medium and high flow models also found individual pieces were found to be defective. These faulty emitters had a measurable effect on the evaluation for those models.
Read more at: http://www.itrc.org/reports/pdf/emitters.pdf
An example of the comparisons that ITRC canbee seen here of their results, compared to the manufacturers' values:
- Author: Ben Faber
Presented by
California Avocado Society, Inc., California Avocado Commission, and University of California Cooperative Extension
California Avocado Growers Seminars Series 2018
Scheduled Dates and Topics
February Seminar Topic
Pest Monitoring and Management
Speakers:
Tuesday, February 6, 2018, 1:00 p.m. to 3:00 p.m.,
UC Cooperative Extension Office Auditorium, 2156 Sierra Way, San Luis Obispo, CA 93401
Wednesday, February 7, 2018, 9:00 a.m. to 11:00 a.m.,
UC Cooperative Extension Office Auditorium, 669 County Square Dr. Ventura, CA 93003
Thursday, February 8, 2018, 1:00 p.m. to 3:00 p.m.,
Fallbrook Public Utility District Board Rm., 990 East Mission Rd. Fallbrook, CA 92028
April Seminar Topic
Old and New Smart Agriculture
Speakers:
Khaled Bali: Irrigation Specialist, Kearney REC
Alireza Pourreza: Ag Engineer, UC Davis
Tim Spann: California Avocado Commission Research Program Director
Dates/Times/Locations:
Tuesday, April 17, 2018, 1:00 p.m. to 3:00 p.m.,
UC Cooperative Extension Office Auditorium, 2156 Sierra Way, San Luis Obispo, CA 93401
Wednesday, April 18, 2018, 9:00 a.m. to 11:00 a.m.,
UC Cooperative Extension Office Auditorium, 669 County Square Dr. Ventura, CA 93003
Thursday, April 19, 2018, 1:00 p.m. to 3:00 p.m.,
Fallbrook Public Utility District Board Rm., 990 East Mission Rd. Fallbrook, CA 92028
June Seminar Topic
Irrigation: Selection of Sensors, Emitters, Injectors and Reading Water Reports
Selection of sensors, emitters
Dates/Times/Locations:
Tuesday, June 5, 2018, 1:00 p.m. to 3:00 p.m.,
UC Cooperative Extension Office Auditorium, 2156 Sierra Way, San Luis Obispo, CA 93401
Wednesday, June 6, 2018, 9:00 a.m. to 11:00 a.m.,
UC Cooperative Extension Office Auditorium, 669 County Square Dr. Ventura, CA 93003
Thursday, June 7, 2018, 1:00 p.m. to 3:00 p.m.,
Fallbrook Public Utility District Board Rm., 990 East Mission Rd. Fallbrook, CA 92028
August Seminar Topic
Grower Seminar and Field Tour
Details to come.
Dates/Times/Locations: One site only
Wednesday, August 1, 2018, 10:00 - 2:00 p.m.,
South Coast Research & Extension Center Conference Room, 7601 Irvine Blvd., Irvine, CA 92818
- Author: Ben Faber
So, every few weeks the question comes up of whether to install soil moisture meters which leads to the question of which to buy and install or have installed. And then come the questions of what do the readings mean and why aren't the readings consistent. Or maybe this question arrives after the grower has installed the sensors or system and the values don't conform to a known or knowable pattern.
The first question to the grower is why they want to install soil moisture sensors or a system. Everyone has a different answer which I've always found interesting. Usually it boils down to having more or better information, although it's hard to beat a good old soil auger. Which takes time and labor.
So once that is cleared up, it comes down to what area they want to monitor. Is it an acre, 10 acres, 50 acres, 100 acres, 200 acres, 1,000 etc.? What are the different irrigation blocks, soil types, aspects? How complex is the area that is to be monitored? Do they need one monitoring site or many? Can the information be gathered in the field, or does it need to be accessed from a distance? Linked by hardwire, infrared, cell phone, wifi, satellite, etc.?
Then the question is does the grower do the installation or is it done by a company? And then whatever the case is, who maintains the system and for that matter, who maintains the information? What software is used and who interprets it?
And what sensors are being used: tension, electrical resistance, conductance, capacitance, electromagnetic…….? The list seems to go on and there are no models and brands coming out on a regular basis. And how reliable are the sensors? What's their lifespan? And what are they measuring and in what units? How affected are the readings by salinity and what soil volume are they measuring? And how important is their placement?
This last point is so often overlooked. The sensor needs to be in the active root zone where water is being taken up. Not where it's convenient to read, not where the plants cant use the water. Placement is so often overlooked.
And then how much do you want to spend? $100 per installation, $1000? With a monthly or yearly maintenance fee or none? Who responds when there are problems?
Wow, so yeah, there are lots of questions. Here's a chart that might help categorize some of the questions:
Method |
Cost |
Ease of use |
Accuracy |
Reliability |
Salt-affected |
Stationary |
Gypsum block |
L |
H |
H |
H |
L |
YES |
Tensiometer |
L |
M |
H |
M |
L |
YES |
Portable tensiometer |
M |
M |
H |
M |
L |
NO |
Solid-state tensiometer |
M |
H |
H |
H |
L |
YES |
Time domain reflectometer |
H |
M |
H |
H |
M |
BOTH |
Neutron probe |
H |
L |
H |
H |
L |
YES |
Feel (soil probe) |
L |
H |
H |
H |
L |
NO |
Gravimetric (oven) |
L |
M |
H |
H |
L |
NO |
Conductance |
L |
H |
M |
M |
H |
BOTH |
Capacitance |
M |
H |
M |
H |
M |
BOTH |
H, high; M, medium; L, low
And the good Almond Doctor might help some more:
http://thealmonddoctor.com/2015/07/10/soil-moisture-sensing-systems/
And maybe some of these publications can help sort out what questions to ask
http://calag.ucanr.edu/Archive/?article=ca.v054n03p38
http://calag.ucanr.edu/Archive/?article=ca.v054n03p47
http://anrcatalog.ucanr.edu/Details.aspx?itemNo=21635
Khaled Bali, our Irrigation Specialist at Kearney Research and Education Center near Fresno, is part of a group in the process of evaluating different types and models of soil moisture sensors. He should have a publication that can more accurately sort through the many sensor choices that are available at this time. But in time, there should be more models on the market and new update will be necessary.
The question, though, is to ask yourself how irrigation is being done and how it can be improved. The basics of design, maintenance, distribution uniformity and how scheduling is being currently done – when and how much to apply. Definitely, soil moisture sensors can help, but you gotta know how to use them and maintain them, just like the whole irrigation system.
A grower who uses tensiometers told me that people think of soil sensors as though they were reading a book. Something cut and dried. A simple plot line that you follow. Irrigation is not a book. There are many other subplots to irrigation than just reading the digital face. Looking at the weather, evapotranspiration, the tree, how fast the moisture is depleted, how deep the moisture is being pulled from all contribute to the "sensors" used to irrigate. Use them all. Even though this grower has irrigators on 250 acres of trees, he also checks the orchard tensiometers at least once a week on his own to confirm all of his senses.