- Author: Ben Faber
Recent talks by UC's new irrigation engineers can help shed light on irrigation improvements that also apply to plant health and better orchard management. The Pourreza talk has implications for identifying HLB infected citrus trees, as well as trees in general stress. The Spann presentation shows how avocado growers will be able to adjust fertilizer applications to their orchards. These talks are posted on the California Avocado Society website.
- 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.
- Author: Ben Faber
At a recent CA Avocado Society meeting there was a discussion about bout flowmeters and their selection. Flowmeters measure the volume of water moving through a full-flowing closed pipe and as such are one of the key components of an irrigation system whether drip, microsprinkler or full pressure systems. They are essential for managing irrigation efficiently and for monitoring the performance of the irrigation system. Managing irrigation efficiently requires: (1) knowing how much water the crop has used since the last irrigation (irrigation schedu7ling); and (2) operating the irrigation system to apply only the amount of water desired. A flowmeter gives the grower the information needed to apply only the amount of water required.
A critically overlooked benefit of a flowmeter is that it makes it possible to identify changes in flowrate during the season (measured at the same pressure), which may indicate problems such as clogging of emitters or filters, leaks in the system or problems with the pump or well.
There are several types of flowmeters and each has their pluses and minuses. Propeller meters are the most commonly used, but can pose two potential difficulties: debris in the water and a small loss of pressure which can be a problem with low flow systems. Alternatives are magnetic meters, ultrasonic, turbine and venture meters. Proper selection is based on pipe size, range of flow and pressure loss. But as with everything it depends on proper installation and maintenance.
Attached is a nice little overview by Larry Schwankl on how to choose a flowmeter for your situation.
flow meters
- Author: Ben Faber
In a recent meeting the topic of where to go for irrigation information came up. Well there's no substitute for attending a class in irrigation, such as offered at Cal Poly SLO (http://www.itrc.org/classes/iseclass.htm ,
but here's some written sources to get you started thinking.
http://ciwr.ucanr.edu/california_drought_expertise/droughttips/
http://www.salinitymanagement.org/Salinity%20Management%20Guide/ei/ei_1.html
http://www.avocadosource.com/tools/IrrigationCalculator.asp
http://lawr.ucdavis.edu/cooperative-extension/irrigation/manuals
http://lawr.ucdavis.edu/cooperative-extension/irrigation/drought-tips
http://biomet.ucdavis.edu/index.php/evapotranspiration-mainmenu-32
http://www.fresnostate.edu/jcast/cit/goods/
http://edis.ifas.ufl.edu/topic_citrus_irrigation
http://edis.ifas.ufl.edu/results.html?q=irrigation&x=0&y=0#gsc.tab=0&gsc.q=irrigation&gsc.page=1
X
- Author: Ben Faber
So after five years of drought a grower told me he finally gets it. Farming avocados in Goleta with limited well water and poor quality and expensive, rationed delivery, he has finally cut out trees that were not performing well. These were wind sept trees, areas with root and crown rot. Tree were either stumped or removed altogether. The idea is to focus on those trees that are productive, and are they ever. They are getting the water they need and their schedule has been changed. Previously irrigation had been on a fixed schedule of 2 weeks and got 24 hours per set. The schedule was dictated by the time it took to get around to all 300 acres. Now trees are irrigated one to two times per week with shorter sets, from 5-8 hours depending on the time it takes to get 18 inches of penetration in sandy ground. Yields per acre have significantly increased, largely because non-productive areas have been eliminated and the remaining trees are getting what they need.
He is also anticipating irrigation needs – projecting a schedule.
The driving forces for water loss in avocados in decreasing effect are sunlight (day length, cloud cover), wind, humidity, and temperature. More light, more transpiration. More wind, more water loss, lower humidity, more water loss. And least of all if temperature which is what we normally respond to, but which the tree responds the least. Usually, though the most desiccating conditions occur during periods of high, dry winds that blow out of the Great Basin – the dread Santa Anas or in the case of Santa Barbara the Sundowners. When they start blowing, it's hard to play catchup. It takes a while for water to infiltrate and for the roots to start taking it up and filling all the drained leaves and stems. Now the grower more carefully watches the forecasts and makes sure to get water on before the high demand conditions arrive. With multiple blocks he wants to get all of them wetted to a normal irrigation depth and then it's time to start the cycle over again. He keep an eye on the nearest CIMIS station to see how much the water demand is increasing and adjusts the irrigation frequency. Importantly, h keep your eye on how fast the soil in the root zone is drying out and then makes even smaller and more frequent applications.
When it comes to making the water meet the needs of the trees, he is really customizing each irrigation.