- Author: Ben Faber
Saline Waters - A Growing Problem
Ben Faber
Irrigated agriculture must always contend with salts, but two years without rain and a dry winter forecast, salt is an even more important issue. We rely on winter rainfall to leach the salts from root zones that have accumulated from previous irrigations. Salinity affects plant growth and understanding what it is and how it is measured and evaluated need to be understood.
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 ofSan Buenaventurawater can be seen in the following chart (2005 Annual Report of the City ofSan 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 inSanta BarbaraandVenturaCountiescontain potentially harmful levels of boron for plants. This is not as common a problem inSan DiegoCounty.
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 pomegrantes. 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 TDSEC: 640 ppm=1 dS/m=1000 umhos/cm
Hardness: measure of calcium and magnesium in water expressed as ppm CaCO3
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
- Author: Ben Faber
The Avocado: Botany, Production and Uses, 2nd Edition
By Bruce Shaffer, Nigel Wolstenholme and Anthony Whiley
This brand new book summarizes avocado science and technology and reviews production practices on a worldwide scale. The book is split into 15 chapters and covers all aspects of avocado production and science and includes: history, distribution and uses, taxonomy and botany, propagation, crop management, diseases and insect and mite pests. This book builds on the 2002 edition and includes the works of 45 writers from all over the avocado world.
Avocado book
- Author: Etaferahu Takele
Costs of Orchard Establishment and Production Summary for Avocados in California:
Based on 2011 studies: www.coststudies.ucdavis.edu
Etaferahu Takele, UCCE Area Advisor, Ag. Econ/Farm Management, southern California and Mao Vue, UCCE Staff Research Associate
In fall 2012, we completed and published sample costs and returns studies for establishment and production practices for conventional and organic avocados in the major producing counties. We divided the production regions into two parts to show the differences in production methods and costs especially as related to water prices. The northern part of the growing region includesVentura,Santa BarbaraandSan Luis Obispocounties. The southern part of the growing region includesSan DiegoandRiversidecounties. We developed four studies, two conventional methods and two organic methods, one for each region.
Data for the sample cost studies were obtained from growers, farm advisors, pest control advisors and other agricultural institutions including banks, agricultural appraisers and equipment dealers. The data we obtained were entered into a budget generator program for calculation and development of sample establishment and production costs.
The studies provide the detail assumptions used in the development of establishment and production costs (ref. the above website) Some common assumptions to all of the cost studies include average labor wages with benefits of $14 per hour for manual and irrigation labor and $18 per hour for machine labor. We used a price of $1.07 per pound which is the five-year average obtained from the California Avocado Commission (CAC) to calculate crop value and we assumed an additional $0.20 per pound premium for organic avocados, and used $1.20 per pound for organic avocados crop value.
Table 1 shows the summary of costs of establishment and production and returns per acre by production method, region, and county. Establishment costs include the accumulated net costs (gross returns less costs) during the orchard development period from year 1 to 6. The production costs estimates are for year 7 + when the trees are considered nearly mature and fully yielding. Gross returns are price per pound times yield. Gross margin are returns above operating and cash overhead costs and returns to management are returns above total costs.
Establishment and production costs are higher for San Diego County than any other avocado producing counties for both the conventional and organic production. In conventional production, establishment costs inSan DiegoCountyare higher by 8% above the northern growing region ofVentura,Santa BarbaraandSan Luis Obispocounties and 15% aboveRiversideCounty. Production costs inSan DiegoCountyare higher by 15% aboveVenturaandSanta Barbaracounties and 21% aboveSan Luis Obispoand 18% aboveRiversideCounty. The main difference is accounted for by water cost, which in our study was assumed $1,200 per ac-ft. forSan DiegoCounty, $650 per ac-ft. for Riverside County, $325 per ac-ft. for Ventura and Santa Barbara, and $200 per ac-ft. for San Luis Obispo. According to the local farm advisor, the high water cost in the southern growing region, especially inSan DiegoCounty, is due to various drought years and the loss of shares of water from theColorado River. Other influencing factors that resulted in higher establishment and production costs for San Diego County include lower yields due to wider space planting (145 trees per acre vs. 180 per acre in the northern region) and higher labor costs for material applications on steeper hillsides.
Organic avocado production costs are generally higher than conventional production regardless of the production region. Orchard establishment costs of organic avocados run 11-12% higher in the northern producing region and 12%-14% in the southern region than the conventional production practices. Similarly, production costs run 11%-12% higher in the northern producing region and 10%-12% higher in the southern producing region than conventional production practices. The main differences between conventional and organic productions include material costs, hours spent on labor, and yields. Organic material particularly in fertilization and pest management tends to cost more and require more labor hours for application than conventional materials. For example, organic fertilizers are usually in dry or granular form and have lower amount of nitrogen per pound (feathermeal 12% for organic vs. UN-32% nitrogen for conventional) therefore requires higher application rates and will take longer to apply by hand. Organic pest control such as spinosad ($34 per ounce) for thrips control cost more than conventional insecticide (abamectin $1 per ounce). In addition, organic growers spend more hours hand weeding in the northern region. Gypsum is hand applied for phytopthora root rot treatment in organic production and costs more to apply than potassium phosphite for conventional production. Overall, costs for organic production results in $3,453 more ($2,471 more for fertilization, $348 more for pesticide, $338 more for root rot treatment and $296 more in weeding) than the conventional method in the northern region and costs $3,804 more ($2,846 more for fertilization, $346 more for pesticide and $610 more for root rot treatment) than the conventional method in the southern region.
There is also a yield difference between conventional and organic productions. Yield is generally higher for conventional than organic production methods regardless of the production region. The yield level provided by growers includes 15% more for conventional production methods than the organic production methods for the northern producing region and 14% more in southern producing regions.
Gross returns estimates for organic production in the northern producing region are higher than gross returns in San Diego and Riverside counties for both conventional and organic production. This is due to higher yield attained from the narrow space planting in the northern producing counties (22’x11’=180 trees per acre in the northern producing regions vs. 20’x15’= 145 trees per acre in the southern producing region).
Gross margin (returns above all cash costs) and returns to management (returns above total costs except management) are all positive for both the northern and the southern part of the growing region. However, gross margins are much lower than the northern growing region. Net margins are positive for the northern part of the growing region but are negative for the southern part.
We provided the breakeven prices analyses in Table 2. Given our costs of production estimates and yield assumption of 12,400 and 11,200 pounds per acre for conventional avocados, respectively for Ventura and Santa Barbara counties and San Luis Obispo County the breakeven prices to cover cash costs are $0.47/lb. in Ventura and Santa Barbara counties and $0.46/lb. in San Luis Obispo County. Whereas the breakeven prices to cover all costs are $0.88/lb. for Ventura and Santa Barbara counties and $0.91/lb. for San Luis Obispo County. This means given the $1.07 price per pound of avocados, there will be $0.60/lb. gross margin and $0.19/lb. net margin for Ventura and Santa Barbara counties; and there will be $0.61/lb. gross margin and $$0.16/lb. net margin for San Luis Obispo County.
For organic production, given the cost of production estimates and yield assumption of 10,500 and 9,500 pounds per acre, respectively for Ventura and Santa Barbara counties and San Luis Obispo County, the breakeven price to cover cash costs is $0.65/lb. for all counties (Ventura, Santa Barbara, and San Luis Obispo). The breakeven prices to cover all costs in organic production are $1.16/lb. for Ventura and Santa Barbara counties and $1.22/lb. for San Luis Obispo County. This means that given the $1.27 price per pound of organic avocados, there will be $0.62/lb. gross margin for all counties and $0.11/lb. net margin for Ventura and Santa Barbara counties and $0.05/lb. net margin for San Luis Obispo County.
In the southern producing region, given our costs of production estimates and yield assumption of 9,000 pounds per acre for conventional avocados for both San Diego and Riverside counties, the breakeven prices to cover cash costs are $1.01/lb. for San Diego and $0.79/lb. for Riverside. Whereas, the breakeven prices to cover all costs are $1.44/lb. for San Diego County and $1.18/lb. for Riverside County. This means that given the $1.07 price per pound of avocados, there will be $0.06 per pound gross margin for San Diego County and $0.28/lb. gross margin for Riverside County. However, the breakeven price falls short by -$0.17/lb. and -$0.11/lb. net margin, respective for San Diego and Riverside counties.
Given our costs of production estimates and yield assumption of 7,700 pounds per acre for organic avocados, for San Diego and Riverside counties, the breakeven prices to cover cash costs are $1.31/lb. for San Diego and $1.05/lb. for Riverside. The breakeven prices to cover all costs are $1.87/lb. for San Diego County and $1.57/lb. for Riverside County. This means that given the $1.27 price per pound of organic avocados, there will be a shortfall of -$0.04/lb. gross margin for San Diego County but a positive gross margin of $0.22/lb. for Riverside County. Net margins fall short of the breakeven prices by -$0.60/lb. and -$0.30/lb., respectively for San Diego and Riverside counties.
Overall, narrow space planting with higher yields and lower water costs are positive impacts on returns to management in the northern producing region with substantial profitability levels that keeps the industry moving forward. On the other hand, the wider spacing and lower yield and higher water costs have negatively affected the overall returns to management in the southern producing region. Currently, there is a trial in the southern producing region on narrow spacing with an emphasis on pruning methods. In the future, we hope to develop a thorough costs study on narrow spacing in the southern producing region after trials are completed. For detail information on our assumptions, costs tables, and profitability analyses copies of the avocado costs studies for both regions on conventional and organic avocados can be retrieve from the above referenced website.
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- Author: Craig Kallsen
A sure way to generate controversy among citrus growers is to initiate a discussion on navel orange tree pruning. Some growers maintain that yield and fruit size is best maintained by minimal pruning, while others believe that the number of large fruit is increased when trees are severely pruned. A ‘standard’ manual pruning for navel oranges does not exist, but the closest thing to it is a procedure that involves pruning from the tree; 1.) shaded, dead branches 2.) branches which cross from one side of the tree to the other and 3.) green, triangular, juvenile shoots from the tree. This type of pruning commonly goes under the name of ‘deadbrushing’. Deadbrushing is a relatively light form of pruning, and a trained crew usually spends less than 15 minutes per tree performing it. In addition to any manual pruning, most navel orange orchards in California are mechanically ‘hedged’ and ‘topped’ to provide continued access to trees and their fruit by equipment and people involved in orchard cultural and harvest activities. Although growers have been growing navel oranges in California for over one hundred years, surprisingly few experiments have been conducted to determine the effect of pruning on navel orange yield and quality.
To assist in providing some guidance related to pruning and its possible effects on fruit yield and quality, an experiment was established in 2000 in northern Kern County in an orange orchard that was typically harvested in late December or in January. In 2000, 2001, 2002 and 2003, yield, fruit quality parameters and manual pruning costs were compared among mature “Frost Nucellar” navel trees (90 trees/acre) having one of three topping-height treatments (14 ft, 16 ft, and untopped trees). In addition to a topping treatment, the experimental trees were given one of three levels of manual pruning 1.) removal of several large scaffold branches in March of 2000 followed by deadbrushing in 2001, 2002 and no manual pruning in 2003; 2. dead brushing only in 2000, 2001, 2002 and no manual pruning in 2003; or 3. no topping or deadbrushing). Data were collected from experimental trees surrounded by similarly topped and manually pruned border trees. Fruit weight, numbers, size, grade and color were determined the day after harvest at theUniversityofCalifornia ResearchandExtensionCenterexperimental packline near Lindcove,California. The year, in this report, refers to the year that the crop bloomed and not to the year of harvest.
For the 2003 crop year, even after 4 years, trees that were severely pruned in the spring of 2000 produced less total yield and less fruit in the most valuable-size range (i.e. 88 to 48 fruit/carton) than trees that were deadbrushed or left unpruned. In 2003, differences in yield among manual pruning treatments were greater than in 2002 probably because of the higher yield potential that appeared to exist across the industry in 2003. The canopy of the severely pruned trees in 2003 had not yet retained the size of the deadbrushed or unpruned trees after four years, which limited their potential fruit production. In contrast, in 2001 only one year after the manual treatments were imposed and a year with high spring temperatures and very poor fruit set, no differences in yield were found among manual pruning treatments.
When the data of average individual tree performance are summed over the four years that this experiment was conducted, the treatment that included removal of some major scaffold branches in March of 2000 with deadbrushing in 2001 and 2002, was inferior in terms of yield, fruit number, and number of valuable-sized fruit in the range of 88 to 48 per carton than to trees that were only deadbrushed or those that had no manual pruning. Most of the detrimental effects of severe pruning on yield (and on fruit quality) occurred at the December harvest following the severe pruning in March 2000. Over the four years of the experiment, the trees that were not manually pruned produced equal or better cumulative yields of fruit, equal or more valuable sized fruit, and fruit with equal grade compared to deadbrushed or severely pruned trees. The percentage of the fruit on the tree larger than size 88 was greater in the severe pruning treatment, but because total fruit number per tree was less and more of this fruit was overly large (i.e. greater than size 48) the number of the most valuable-sized fruit/tree (sized 88 to 48) was less. Obviously, the trees that were not manually pruned had no associated manual pruning costs when compared to the other two pruning treatments. Manual pruning costs, from 2000 through 2003, not including stacking and shredding of pruned brush, were $8.50/tree for the deadbrushing treatment and $13.00/tree for the severe manual pruning treatment.
Fruit yield or quality was not different among topping heights in any of the four years of the experiment. Topping height did not affect yield, probably because of the wide spacing and tall trees in this orchard. The canopies of untopped trees had little fruit within 4 feet of the ground as a result of shading of the lower canopy by neighboring trees. Removing the top 4 feet from an 18-foot tall tree moved the fruit-bearing volume downward in response to greater light penetration into the lower canopy but did not decrease the volume of the tree that received sufficient light to produce fruit. This effect was in contrast to severe manual pruning, which reduced the volume of the unshaded canopy overall, limiting the volume available for fruit production. A highly significant positive-linear correlation was found in the data across the four years and treatments between the total numbers of fruit produced per acre versus the total number of fruit sized 88 to 48 per carton produced per acre. This functional relationship existed whether reductions in fruit numbers produced per acre were the result of severe pruning in March or from weather-related phenomena such as occurred in 2001, suggesting that anything that reduced fruit numbers below approximately 130,000 fruit per acre resulted in a decrease in the number of fruit sized 88 to 48 per carton in this orchard.
Of course, there are other reasons to manually prune orange trees, other than to improve fruit size. If certain insects, likeCaliforniared scale or cottony cushion scale have been a problem, pesticide spray coverage may be improved by making the canopy less dense through pruning and fruit quality may be improved by making this investment. In general, what this pruning research has reinforced is the concept that growers should know why they are pruning orange trees and that manual pruning is unlikely to increase the number of fruit in the most valuable size ranges.
- Author: Ben Faber
"We don't need to irrigate, it's winter." This is a commonly held idea, and many years it is true. Adequately timed rains will often meet the needs of avocado trees during the winter period, and in times like last year, even satisfy much of the spring requirement. And the calls are coming in – “What’s wrong with my trees, they have all these brown leaves?”. This from San Diego to San Luis Obispo.
In a low rainfall year, irrigation can be as necessary as at other times of the year. This is because a subtropical evergreen like avocado continues to use water regardless of rainfall patterns. At the time of writing this article in March, we have had a scant 4 inches in Ventura and this is on top of a low rainfall year in 2011-12. Rain is necessary to leach the salts that have accumulated from the last irrigation season.
The driving forces for plant water use are light intensity, wind and relative humidity, as well as temperature. Remember how cold, dry winds can dry your skin or freeze-dry backpack food. Even during the winter, the trees are quite capable of losing large amounts of water with clear skies and cold winds.
Dry Santa Ana conditions are also more common in winter than in the past. This winter, a time of drought, I went out to see an orchard to evaluate it for pruning. On arrival, my first concern was for the water stress in the trees. The grower, however, was unconcerned. The trees had been dutifully irrigated the previous Friday. But over the weekend, a Santa Ana had blown for three days and completely dried the soil in the top 10 inches. Digging around the roots convinced the grower of water stress. Do not take irrigation for granted.
Contributing to the problem is the determination of what amount of rainfall is effective. Effective rainfall is defined as the amount of water that is retained in the root zone after rain. Avocados, especially on shallow soils, do not have much of a root zone. Most soils can be expected to hold about 2 inches of available water in the top 2 feet, less the more sandy, more the more heavy.
If rainfall exceeds the holding capacity within the root zone, it is lost to the plant. Just imagine if all the year's expected rain fell during one storm. It would not be long before irrigation would be required with no more rain coming. The extra water may, however, perform the all-necessary function of leaching accumulated salts from the root zone. When the rain gauge says that 2 inches fell, it is quite possible that all that rain will not be available to the tree. This also goes for the quarter inch storms we get that do not even make it through the leaf litter. It is not effective rainfall, even though it may wash the persea mite off the leaves.
One of the best ways to assess the effectiveness of rainfall within the root zone is with tensiometers. These trusty instruments are most commonly used to schedule irrigations. A good rainfall should return the 8- and 18-inch depth gauges to close to 0 cbars. This will tell you whether the rain thoroughly wetted the root zone. It will not tell you how much may have passed through the root zone, however.
If you are using soil sampling to assess the depth of rain infiltration, simply squeezing a handful of soil can help. Regardless of soil texture, a wetted soil will form a ball or cast when thoroughly wetted. Water moves as a front through the soil. After a rain, take soil samples with depth to find where the potential to form a ball abruptly ends. This will tell you the depth of effective rain.
How well a soil holds together can also be an indication of when to irrigate. Even a sandy loam texture will retain a ball that does not hold together well when there is still adequate moisture for the tree. The possibility of forming a ball decreases with water content. When visible cracking of a soil ball is obvious, it is time to irrigate.
Winter irrigation is something we do not commonly perform, but in low rainfall years it is an activity we need to consider, especially for controlling the salts that accumulate from our previous irrigation season.
Salt damage due to lack of leaching