Subtropical Fruit Crops Research & Education
University of California
Subtropical Fruit Crops Research & Education

Posts Tagged: irrigation

It's NOt Just Water, It's Salt

Irrigated agriculture must always contend with salts. Five years of drought and its effects can magically disappear, but it will be back again. Low rainfall is the norm for California. We rely on winter rainfall to leach the salts from root zones that have accumulated salts from previous irrigations.  Salinity affects plant growth and understanding what it is and how it is measured and evaluated need to be understood.  Just having wet soil that is full of salts is not going to help a plant, it's going to add stress and eventually physiological and disease problems - https://ucanr.edu/blogs/Topics/index.cfm?start=28&tagname=disease

All waters, even rain water, have some salts dissolved in them, so all waters could be called saline.  The term saline is restricted to waters with concentrations that could cause harm to plants or people.  Seawater is highly saline, many wells are moderately saline.  But unlike humans that excrete salts, plants are often affected by salt levels that have very little health impact on humans. Well waters used for irrigation can often exceed standards for plants that are fit for human consumption.  However, with proper management many waters can be used on plants, depending on the plant species.  Domestic water supplies from cities typically have better quality than some well waters because they are monitored and often blended to meet human consumption.  Most domestic water supplies have low concentrations of salts and are not considered to be saline.  However, using even domestic water in growing subtropicals does not mean that we should not be concerned about salinity.

Before going any further it is worth remembering that salt is not just the sodium chloride that's on the table.  Salts are combinations of electrically charged ions.  These ions separate from one another when a salt dissolves in water.  Water with dissolved sodium chloride and potassium nitrate contains sodium, potassium, chloride and nitrate ions.  The most common ions in natural waters are:

 

            sodium (Na+)              chloride(Cl-)    sulfate (SO42-)

            calcium (Ca+)             boron (H3BO3)

            magnesium (Mg+)      bicarbonate (HCO3-)

                                                                                            

Different waters can have very different proportions of these ions and these proportions can change with time.  Some typical analyses of City of San Buenaventura water can be seen in the following chart (2015 Annual Report of the City of San Buenaventura).

 

Ionic composition of some wells in Ventura

 

Sample

Na+

Ca+

Mg+

Cl-

SO42-

TDS

EC

 

 

 

(mg/l)

 

 

 

(umhos/cm)

1

200

259

70

92

839

1668

1990

2

45

92

191

44

210

645

874

3

28

59

21

20

140

316

580

 

Total dissolved solids (TDS) and electrical conductivity (EC) are two different ways of measuring the total amount of salts in water.  The old way of taking a specified volume (l for liter) of water and boiling it down to the residue which is weighed (mg for milligram) gives TDS.  The more modern technique is to measure the electrical current a water will carry (umhos/cm or micromhos/cm), which is in proportion to the number of ions in the water.

Natural waters also contain low concentrations of many other elements.  For most, the amounts are too low to be either harmful or beneficial to plants.  The main exception is boron which can be a problem for sensitive plants, such as citrus and avocado and probably for cherimoya as well, when in excess of 1 mg/l.  Many well waters in Santa Barbara and Ventura Counties contain potentially harmful levels of boron for plants.  This is not as common a problem in San Diego County.

In addition to the ions mentioned, there are also those that come from fertilizers and the soil.  The main extra ions are potassium, ammonium, nitrate and phosphate.  The concentrations of these will depend on the type of soil and the amounts and kinds of fertilizers applied, minus the amounts taken out by plants, held by the soil and lost by leaching or erosion.

In evaluating a water for its potential to harm plants, it is necessary to look at total salinity, as well as the specific ions.  Waters with a TDS in excess of 1000 mg/l or an EC greater than 1500 umhos/cm might pose problems for sensitive subtropical plants, and none at all to tolerant plants like figs, apricots or pomegranates.  Waters with an excess of sodium and/or chloride (more than 100 mg/l) can induce symptoms that are similar to high levels of salinity.

In most cases, plants respond by initially having their leaf margins turn yellow and die.  This happens first on older leaves because they have had the longest time to accumulate the ions.  Annual plants are often less affected than perennials, since they do not grow long enough to accumulate sufficient ions to cause damage.

As trees remove water from the soil, the concentration of salts in the remaining soil water increases.  Plants adapt to moderate increases, but if the plant is sensitive (and most subtropicals are), it will slow growth in response.  If the salt increase is small, the growth reduction will be small and acceptable.  But if the level of fertilizer use is high, the water quality poor, or the soil has not been properly leached, the increased soil salinity could reduce growth seriously.

The effects of salinity are usually gradual on plants, unless too much fertilizer has been suddenly applied or strong, dry winds causes rapid drying.  Also, with some domestic water there is variation in concentration and kinds of salts in the water with time.  The 200 mg/l of sodium in water sample 1 on the chart would be a problem if this were what the homeowner continuously received.  However, according to city data, this house does get 94 mg/l at times (not on the chart).  The better quality water serves to flush out the higher concentration salts.  And this is how to practically deal with poorer quality water, occasionally leach the soil with a volume of water in excess of plant need.  When there are no leaching rains, we need to be more aware of the potential for salt accumulation in the soil.  With proper plant selection and water management even extremely saline waters can be used.

 

Water Terminology

 

The ions in water are measured as parts per million (ppm) or milligrams per liter (mg/l), terms which are interchangeable.  This is like saying a percent, but instead of the ions' weight per 100 weight of water, it is the ions' weight per million weight of water.  The ion concentration also can appear as milliequivalents per liter (meq/l).  A milliequivalent is the ppm of that ion divided by its atomic weight per charge. 

            Example:  Ca2+ with atomic weight of 40 and a solution concentration of possibly 200 ppm.  Ca2+ has two charges per atom, so it has an atomic weight of 20 per charge.  200 ppm divided by 20 = 10 meq of calcium for a liter of water.

Total Dissolved Solids (TDS): measure of total salts in solution in ppm or mg/L

Electrical Conductivity (EC):  similar to TDS but analyzed differently.

            Units: deciSiemens/meter(dS/m)=millimhos/centimeter (mmhos/cm)=

                                    1000 micromhos/cm (umhos/cm).

            Conversion TDS to EC:  640 ppm=1 dS/m=1000 umhos/cm

Hardness:  measure of calcium and magnesium in water expressed as ppm CaCO

pH:  measure of how acid or base the solution

Alkalinity:  measure of the amount of carbonate and bicarbonate controlling the pH, expressed as ppm CaCO3.

Sodium Adsorption Ratio (SAR):  describes the relative sodium hazard of water

                        SAR= (Na)/((Ca+Mg)/2)1/2, all units in meq/l

            There is also an Adjusted SAR which considers the carbonate and bicarbonate present, but does not do much better in predicting plant response.

 

General Irrigation Quality Guidelines

(U.C. Leaflet 2995, 1979)

 

Measurement                          No problem                 Increasing                   Unsuitable

Effect on plant growth

EC (dS/m)                                  3

Na+ (SAR)                                   9

Cl- (ppm)                                 140                               140-350                         >350

H3BO3 (ppm)                               2

 

Effect on soil permeability

EC (dS/m)                                    >0.5                       

SAR                                               9

 

 

1.5 feet of water with EC of 1.6 dS/m adds 10,000 # of salt per acre

WATER NEEDS TO BE APPLIED NOT ONLY FOR THE PLANT NEED,

BUT ALSO TO LEACH THE SALTS

salt pile
salt pile

avocado salt damage
avocado salt damage

Posted on Friday, April 26, 2019 at 6:30 AM
Tags: irrigation (76), leaching (3), salt (7)

It's NOT Just Heat Stress, It's Lack of Water for Cooling

Plants lose water through their leaves and it's called transpiration.  People lose water off their skin and it's called evaporation or sweating.  When a plant stops losing water and when people cant produce enough sweat to cool off, both overheat.  The weather influences that drive this water loss - water that needs to be replaced or the bodies begin to go into heat stress - are the amount of light (day length, cloud cover), relative humidity (it dries faster when air is dry and slower when humid - think desert versus Florida),  and windy (more wind, more drying).  Temperature is important, but not as much as these other drivers. Think freeze-drying  - a very successful process for removing water from food.  Often humans respond more to temperature than these other factors and figure, when it's cool. it's not necessary to water their plants, themselves or their workers.

Heat stress is more complicated than this, of course, but below are some helpful guidelines to follow to avoid heat stress:

https://www.dir.ca.gov/dosh/heatillnessinfo.html

Cal/OSHA HEAT ADVISORY

When employees work in hot conditions, employers must take special precautions in order to prevent heat illness. Heat illness can progress to heat stroke and be fatal, especially when emergency treatment is delayed. An effective approach to heat illness is vital to protecting the lives of California workers.

California law requires employers to identify and evaluate workplace hazards and take the steps necessary to address them. The risk of heat illness can be significantly reduced by consistently following just a few simple steps. Employers of outdoor workers at temporary work locations must be particularly alert and also plan for providing first aid and emergency medical services should they become necessary. All workers should be accounted for during and at the end of the work shift. Heat illness results from a combination of factors including environmental temperature and humidity, direct radiant heat from the sun or other sources, air speed, and workload. Personal factors, such as age, weight, level of fitness, medical condition, use of medications and alcohol, and acclimatization effect how well the body deals with excess heat. 

Heat Illness Risk Reduction

1. Recognize the Hazard. There is no absolute cut-off below which work in heat is not a risk. With heavy work at high relative humidity or if workers are wearing protective clothing, even work at 70oF can present a risk. In the relative humidity levels often found in hot areas of California (20 to 40 percent) employers need to take some actions to effectively reduce heat illness risk when temperatures approach 80 F. At temperatures above 90 F, especially with heavy work, heat risk reduction needs to be a major concern.

    2. Water. There must be an adequate supply of clean, cool, potable water. Employees who are working in the heat need to drink 3-4 glasses of water per hour, including at the start of the shift, in order to replace the water lost to sweat. For an eight-hour day this means employers must provide two or more gallons per person.  Thirst is an unreliable indicator of dehydration. Employees often need ongoing encouragement to consume adequate fluids, especially when the workload or process does not encourage breaks.

3. Shade. The direct heat of the sun can add as much as 15 degrees to the heat index. If possible, work should be performed in the shade. If not, employers where possible, should provide a shaded area for breaks and when employees need relief from the sun. Wide brimmed hats can also decrease the impact of direct heat.

  1.  Acclimatization. People need time for their bodies to adjust to working in heat. This “acclimatization” is particularly important for employees returning to work after (1) a prolonged absence, (2) recent illness, or (3) recently moving from a cool to a hot climate. For heavy work under very hot conditions, a period of 4 to 10 days of progressively increasing work time starting with about 2 hours work per day under the working conditions is recommended. For less severe conditions at least the first 2 or 3 days of work in the heat should be limited to 2 to 4 hours. Monitor employees closely for signs and symptoms of heat illness, particularly when they have not been working in heat for the last few days, and when a heat wave occurs. 
  2.  Rest Breaks. Rest breaks are important to reduce internal heat load and provide time for cooling. Heat illness occurs due to a combination of environmental and internal heat that cannot be adequately dissipated. Breaks should be taken in cooler, shaded areas. Rest breaks also provide an opportunity to drink water.
  3.  Prompt Medical Attention. Recognizing the symptoms of heat illness and providing an effective response requires promptly acting on early warning signs. Common early symptoms and signs of heat illness include headache, muscle cramps, and unusual fatigue. However, progression to more serious illness can be rapid and can include unusual behavior, nausea/vomiting, weakness, rapid pulse excessive sweating or hot dry skin, seizures, and fainting or loss of consciousness. Any of these symptoms require immediate attention.

Even the initial symptoms may indicate serious heat exposure. If medical personnel are not immediately available on-site, and you suspect severe heat illness, you must call 911.

Regardless of the worker's protests, no employee with any of the symptoms of possible serious heat illness noted above should be sent home or left unattended without medical assessment and authorization.

7. Training. Supervisors and employees must be trained in the risks of heat illness, and the measures to protect themselves and their co-workers. Training should include:

  • Why it is important to prevent heat illness
  • Procedures for acclimatization
  • The need to drink approximately one quart per hour of water to replace fluids.
  • The need to take breaks out of the heat
  • How to recognize the symptoms of heat illness
  • How to contact emergency services, and how to effectively report the work location to 911.

Photo: Heat Stress to avocado leaves.

heat damage to avocado leaves
heat damage to avocado leaves

Posted on Friday, April 12, 2019 at 3:18 PM

Citrus? Water? How Do They Go Together?

Advances in Citrus Water Use

                         Workshop & Field Day

Tuesday, March 26, 2019

8 Am - 3 PM

Strathmore, CA

 

Attend the Advances in Citrus Water Use Workshop & Field Day and join UC Davis Irrigation Specialist Daniele Zaccaria as well as other water experts and specialists from the University of California Cooperative Extension, the California Department of Water Resources, and the Citrus Research Board to learn about research advances in water use and irrigation for citrus production. Gain firsthand practical knowledge of the latest developments in the citrus industry and become familiar with methods and tools to measure evapotranspiration (ET) and crop coefficients (Kc), tree water status, and monitor soil moisture to inform irrigation planning and scheduling decisions for citrus. 

 

What to expect?

Session topics include:

  • Current research
  • Water management and regulation
  • Optional Field Session on irrigation technology

View a tentative agenda here.

 

 

Registration Details

 

$35 registration fee includes admission to the field day, coffee, refreshments, and lunch.

 

 

 

Register online, here. Fee will increase on March 13.

 

 

Limited to the first 150 participants

 

 

Logistics and Registration

ANR Program Support, Julia Kalika, (530) 750-1380 or Shannon Martin, (530) 750-1328

citrus cornucopia
citrus cornucopia

Posted on Friday, March 8, 2019 at 1:44 PM
Tags: citrus (310), irrigation (76), water (48)

Water is Life and Watering Citrus is Critical - Come Learn

Advances in Citrus Water Use

               Workshop & Field Day

Tuesday, March 26, 2019

8:00 AM-3:00 PM

Strathmore, California

Register NOW!!!

 https://ucanr.edu/sites/citrusfieldday/Registration/

About the Field Day

 

Attend the Advances in Citrus Water Use Workshop & Field Day and join UC Davis Irrigation Specialist Daniele Zaccaria as well as other water experts and specialists from the University of California Cooperative Extension, the California Department of Water Resources, and the Citrus Research Board to learn about research advances in water use and irrigation for citrus production. Gain firsthand practical knowledge of the latest developments in the citrus industry and become familiar with methods and tools to measure evapotranspiration (ET) and crop coefficients (Kc), tree water status, and monitor soil moisture to inform irrigation planning and scheduling decisions for citrus. 

 

What to expect?

Session topics include:

  • Current research
  • Water management and regulation
  • Optional Field Session on irrigation technology

View a tentative agenda here.

Registration Details

$35 registration fee includes admission to the field day, coffee, refreshments, and lunch.

 

Register online, here. Fee will increase on March 13.

 

Limited to the first 150 participants.

Contacts for More Information

 

Logistics and Registration

ANR Program Support, Julia Kalika, (530) 750-1380 or Shannon Martin, (530) 750-1328.

 

Course Content 

Daniele Zaccaria, UC Cooperative Extension Specialist, Agricultural Water Management

 

citrus cornucopia
citrus cornucopia

Posted on Friday, March 8, 2019 at 1:26 PM
Tags: citrus (310), field day (4), irrigation (76), water (48)

Frost and Rain?

It is that time of year and we should be alert to threat of freezing weather and damage to trees. Last winter was one of the warmest on record, but there was still a sneak cold blast around December 25 that caused some problems in some areas. Wet winters tend to have lower frost threats, and even though wet is forecast for this winter, the forecast is erratic, as usual. That still leaves January which historically is when most of our damaging frosts occur. Fox Weather on the CA Avocado Commission is forecasting some cold weather coming up, so growers need to be prepared for the worst.

http://www.californiaavocadogrowers.com/articles/30-day-weather-outlook-december-7-2015-january-7-2015

 

Here are some links to frost information, preparing for frost and managing frost damage to trees.

A Frost Primer

http://ceventura.ucanr.edu/Com_Ag/Subtropical/Publications/Frost/A_Frost_Primer_-_2002_/

Methods of Frost Protection

http://ceventura.ucanr.edu/Com_Ag/Subtropical/Avocado_Handbook/Frost_Control_Freeze_Damage_/Methods_of_Frost_Protection_/


Protecting Avocados from Frost

http://ceventura.ucanr.edu/Com_Ag/Subtropical/Avocado_Handbook/Frost_Control_Freeze_Damage_/Protecting_Avocados_from_Frost_/


Rehabilitation of Freeze-Damaged Citrus and Avocado Trees

http://ceventura.ucanr.edu/Com_Ag/Subtropical/Avocado_Handbook/Frost_Control_Freeze_Damage_/Rehabilitation_of_Freeze-Damaged_Citrus_and_Avocado_Trees_/

The forecast is for north winds, which often means cold, dry air and often with winds. Winds mean no inversion and no warm air that can be introduced at ground level to warm trees. If this occurs, running a wind machine can make the damage worse. Wind machines and orchard heaters work on the principle of mixing that warmer air higher up – 20-100 or so feet higher than ground level which has colder air. When temperatures drop, the air is dry (wet-bulb temp below 28 deg F) and there is no inversion, running a wind machine can just stir up cold air and cause worse conditions (freeze-drying). It's better to not run the machine. The only thing left to do is to run the microsprinklers during the day so that the water can absorb the day's heat. Then turn the water off before sunset so that evaporative cooling from the running water isn't accentuated. Then when temperatures drop near 32 at night and the dewpoint is much below that, it's time to start the water again and let it run until sunrise (when risk is less). Running water works even if the water freezes. This is due to the release of heat when water goes from liquid to frozen state. This 1-2 degrees can mean the difference between frost damage and no damage. Also, ice on fruit and leaves can insulate the fruit. As the ice melts at the surface of the plant, it releases heat, protecting the plants. If there is not sufficient water to run the whole orchard, it's best to pick out the irrigation blocks that are the coldest or the ones you definitely want to save and run the water there continuously. Running the water and turning it off during the night to irrigate another block can lead to colder temperatures in both blocks.

 

Keep warm this winter.

and check out this Wind Machine You Tube:

https://www.youtube.com/watch?v=rwTJveN8cIE

Wind Machine frost
Wind Machine frost

Posted on Wednesday, January 9, 2019 at 4:46 PM
Tags: avocado (275), citrus (310), frost (17), irrigation (76), water (48), wind (5)

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