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

Posts Tagged: toxicity

Now is the Time to Sample Citrus for Nutrients - and Avocados Too

University of California (UC) researchers and private industry consultants have invested much effort in correlating optimal citrus tree growth, fruit quality and yield to concentrations of necessary plant nutrients in citrus (especially orange) leaf tissue. The grower can remove much of the guesswork of fertilization by adhering to UC recommendations of critical levels of nutrients in the tissues of appropriately sampled leaves.  Optimal values for elements important in plant nutrition are presented on a dry-weight basis in Table 1.  Adding them in appropriate rates by broadcasting to the soil, fertigating through the irrigation system or spraying them foliarly may correct concentrations of nutrients in the deficient or low range.  Compared to the cost of fertilizers, and the loss of fruit yield and quality that can occur as a result of nutrient deficiencies or excesses, leaf tissue analysis is a bargain.   At a minimum, the grower should monitor the nitrogen status of the grove through tissue sampling on an annual basis.

Leaves of the spring flush are sampled during the time period from about August 15 through October 15.  Pick healthy, undamaged leaves that are 4-6 months old on non-fruiting branches.  Select leaves that reflect the average size leaf for the spring flush and do not pick the terminal leaf of a branch.  Typically 75 to 100 leaves from a uniform 20- acre block of citrus are sufficient for testing. Generally, the sampler will walk diagonally across the area to be sampled, and randomly pick leaves, one per tree.  Leaves should be taken so that the final sample includes roughly the same number of leaves from each of the four quadrants of the tree canopy.  Values in Table 1 will not reflect the nutritional status of the orchard if these sampling guidelines are not followed. Typically, citrus is able to store considerable quantities of nutrients in the tree.  Sampling leaves from trees more frequently than once a year in the fall is usually unnecessary.  A single annual sample in the fall provides ample time for detecting and correcting developing deficiencies.

 

Table 1.  Mineral nutrition standards for leaves from mature orange trees based on dry-weight concentration of elements in 4 to 7 month old spring flush leaves from non-fruiting branch terminals.

element

unit

deficiency

low

optimum

high

excess

 

 

 

 

 

 

 

N

%

2.2

2.2-2.4

2.5-2.7

2.7-2.8

3.0

P

%

0.9

0.9-0.11

0.12-0.16

0.17-0.29

0.3

K (Calif.*)

%

0.40

0.40-0.69

0.70-1.09

1.1-2.0

2.3

K (Florida*)

%

0.7

0.7-1.1

1.2-1.7

1.8-2.3

2.4

Ca

%

1.5

1.6-2.9

3.0-5.5

5.6-6.9

7.0

Mg

%

0.16

0.16-0.25

0.26-0.6

0.7-1.1

1.2

S

%

0.14

0.14-0.19

0.2-0.3

0.4-0.5

0.6

Cl

%

?

?

<0.03

0.4-0.6

0.7

Na

%

?

?

<0.16

0.17-0.24

0.25

B

ppm

21

21-30

31-100

101.260

260

Fe

ppm

36

36-59

60-120

130-200

250?

Mn

ppm

16

16-24

25-200

300-500?

1000

Zn

ppm

16

16-24

25-100

110-200

300

Cu

ppm

3.6

3.6-4.9

5 - 16

17-22?

22

*California and Florida recommendations for K are sufficiently different that they are presented separately.  The California standards are based on production of table navels and Valencias, and those for Florida were developed primarily for juice oranges like Valencia.

 

The sampled leaves should be placed in a paper bag, and protected from excessive heat (like in a hot trunk or cab) during the day.  If possible, find a laboratory that will wash the leaves as part of their procedure instead of requiring the sampler to do this.  Leaf samples can be held in the refrigerator (not the freezer) overnight.  Leaves should be taken to the lab for washing and analysis as quickly as is feasible.

Often separate samples are taken  within a block if areas exist that appear to have special nutrient problems.  The temptation encountered in sampling areas with weak trees is to take the worst looking, most severely chlorotic or necrotic leaves on the tree.  Selecting this type of leaf may be counter-productive in that the tree may have already reabsorbed most of the nutrients from these leaves before they were sampled. A leaf-tissue analysis based on leaves like this often results in a report of general starvation, and the true cause of the tree decline if the result of a single nutritional deficiency may not be obvious.  Often in weak areas, it is beneficial to sample normal appearing or slightly affected leaves.  If the problem is a deficiency, the nutrient will, generally, be deficient in the healthy-looking tissue as well.

Groves of early navels that are not normally treated with copper and lime as a fungicide should include an analysis for copper. Copper deficiency is a real possibility on trees growing in sandy, organic, or calcareous soils.  For later harvested varieties, leaves should be sampled before fall fungicidal or nutritional sprays are applied because nutrients adhering to the exterior of leaves will give an inaccurate picture of the actual nutritional status of the tree.

Usually leaf samples taken from trees deficient in nitrogen will overestimate the true quantity of nitrogen storage in the trees. Trees deficient in nitrogen typically rob nitrogen from older leaves to use in the production of new leaves.  Frequently, by the time fall leaf samples are collected in nitrogen deficient groves, these spent spring flush leaves have already fallen.  Nitrogen deficient trees typically have thin-looking canopies as a result of this physiological response.  Since the spring flush leaves are no longer present on the tree in the fall when leaves are sampled, younger leaves are often taken by mistake for analysis. These leaves are higher in nitrogen than the now missing spring flush leaves would have been and provide an inaccurately higher nitrogen status in the grove than actually exists.

Critical levels for leaf-nitrogen for some varieties of citrus, like the grapefruits, pummelos, pummelo x grapefruit hybrids and the mandarins, have not been investigated as well as those for oranges.  However, the mineral nutrient requirements of most citrus varieties are probably similar to those for sweet oranges presented in Table 1, except for lemons, where the recommended nitrogen dry-weight percentage is in the range of 2.2- 2.4%.

A complete soil sample in conjunction with the leaf sample can provide valuable information on the native fertility of the soil with respect to some mineral nutrients and information on how best to amend the soil if necessary to improve uptake of fertilizers and improve water infiltration.

P.S. from Ben Faber

What has been said here about citrus is also generally true for avocado, although the nitrogen sufficiency levels are lower than for citrus.  For a more detailed discussion see: http://www.californiaavocadogrowers.com/sites/default/files/documents/11-Final-Report-Issued-Giving-Tools-for-Fertilization-and-Salinity-Management-Winter-2016.pdf

Photo: Nitrogen deficient avocado leaf

nitrogen avocado
nitrogen avocado

Posted on Wednesday, August 23, 2017 at 5:35 AM
  • Author: Craig Kallsen

Putting Fertilizer Chloride in Perspective

Especially when there are no winter rains to leach accumulated salts from the root zone of trees, there is major concern about increasing the levels of salts going into the root zone. Chlorides, boron, sodium and total salts all should be minimized as much as possible in order to optimize tree production and health. Evaluating the fertilizer and irrigation management programs is important and in doing so, finding out how much is being put into the orchard.

A wonderful way to evaluate what is being applied through the irrigation system is to go online to AvocadoSource (avocadosource.com) and go to the ‘Tools' section and click on the ‘Irrigation Water Mineral Content Calculator'. Once there click on ‘Retrieve District Water Analysis Data' and there are several water qualities that can be downloaded onto the calculator.

I chose one of the Metropolitan Water District sources – Castaic Lake – which is representative of water delivered to the south from northern California. It shows a chloride level of 81 mg/L (81 ppm) which translates to 220 pounds of chloride for every acre-foot of water. Which means about 440 pounds of chloride per acre (about 2 ac-ft/ac) to grow avocado and citrus in Fillmore. And the same water coming out of Lake Skinner further south but nearly the same quality as Castaic, would be 880 pounds of chloride per acre in Fallbrook (4 ac-ft/ac).

So the question comes up about the use of potassium fertilizers. Citrus and avocado haul off about twice the potassium in their fruit as nitrogen. A typical harvest for either crop is about 50 pounds of K per acre – more fruit, more K. So to apply potassium, a grower can use several different materials – KMag, potassium thiosulfate, potassium sulfate, potassium nitrate, potassium chloride. A 100 pounds of either potassium sulfate or chloride put on about the same amount of potassium, 50 pounds. With the potassium chloride or course, there is 50 pounds of chloride.

The cheapest source of K is potassium chloride, but growers are concerned about the added chloride. The material is highly soluble and is easily injectable. It also is rapidly moved through the soil, so when it is injected through the irrigation in small amounts, the chloride tends not to accumulate in the root zone. So looking at the total amount of chloride that is applied in our normal irrigation waters, the chloride in the fertilizer doesn't represent a large proportion of the total chloride the tree sees. It could be considered in a fertilizer program, or at least a supplement to other sources of potassium.

Potassium is relatively immobile in soil, more so with more clay. Chloride on the other hand is quite mobile. It goes wherever the water goes. Applying it any time of the year basically results in its staying there until it is taken up or the soil is washed away. So applying potassium chloride in a wetter time of year, could be a cheap way to get potassium on with the least effect of chloride. Or potassium chloride could be applied in rotation with more expensive forms of potassium, such as potassium thiosulfate (KTS).

By the way, that Castaic water would contain 87 ppm sulfate and 74 ppm sodium which would mean over 200 pounds per ac-ft in the water and 110 ppm bicarbonates. The pH would be around 7.8. And this is good water by southern California standards. Many of the well water in southern California have much lower qualities than these waters from norther California and we get good yields from them. We have learned to use some pretty awful waters to grow crops here.

chloride toxicity avocado
chloride toxicity avocado

Posted on Monday, August 10, 2015 at 11:54 AM

One, one hundred, one thousand

This little mnemonic, or memory aid, in the title is helpful in remembering the critical levels of toxic constituents in irrigation water. The “one” stands for 1 part per million (ppm) of boron (B), the e” hundred” flags 100 ppm of sodium (Na) and (Cl) and the “thousand” represents the level of total soluble solids (TDS or slats) in water. Levels exceeding the critical values for any of these constituents can present problems for tree growers. The problems typically show themselves as tip-burn and defoliation. The B, Na and Cl are toxic elements at relatively low concentrations, but symptoms appear similar to the damage caused by high salinity.

 

Water that exceeds the critical levels mentioned in the mnemonic has a greater tendency to cause damage if sufficient leaching is not applied. It doesn't mean the water is impossible to use, only that greater attention needs to be made to ensure that these salts are adequately leached. High levels of these salts accumulate in the soil with each irrigation, and the salts are absorbed by the tree and end up in the leaves where they do their damage.

 

This promises to be another low rainfall year and the customary leaching we rely upon in winter rainfall is not going to be as effective as in customary years. Irrigation is a necessary evil. Every time we apply irrigation water we apply salts, and unless some technique is used to minimize salt accumulation, damage will result. This damage can be more than just leaf drop, but also the stress that induces conditions for root rot.

 

Irrigation water has been applied the last four years and many trees looked stressed. Even well irrigated orchards have leaf burn due to the gradual accumulation of salts from irrigation. It is probably necessary to irrigate in many winters. With the lack of rain problem, it may be necessary to irrigate even if there is rain. The wetted pattern that is created by a drip or microsprinkler emitter also creates a ring of salt in the outer band of the wetted patter. If there is less than an inch of rainfall to push this salt down, this salt tends to diffuse towards the tree where it can accumulate back in the root system. Orchards with even good water quality would find it advisable to run the irrigation system with the first rains. Growers with water quality exceeding one, hundred, or thousand should be especially alert to the need to manage water in low rainfall years.

irrigATING CITRUS
irrigATING CITRUS

Posted on Wednesday, June 24, 2015 at 10:40 AM
Tags: boron (2), chloride (2), EC (1), salinity (1), salts (1), sodium (1), TDS (1), toxicity (5)

Boron is High in Many Southern San Joaquin Valley Citrus Trees

Many citrus trees in the southern end of the San Joaquin Valley are grown on moderately calcareous soils and frequently have high levels of boron in the leaf tissue.  Citrus is sensitive to boron. Boron, when excessive, may cause defoliation and significant yield loss. At high, but nontoxic concentrations, leaf symptoms are similar to those caused by excessive salt, deficient potassium, heat stress, or biuret toxicity from urea foliar sprays.  Therefore a leaf tissue analysis is important for delineating causes.

Excessive levels of boron produce a yellowing of the tip of leaves and yellow spotting of the leaf surface.  Death of the leaf tissue may occur along the margins. Higher levels of boron may cause brownish, resinous gum spots on undersides of leaves but this symptom is not always present.  Leaf symptoms are most severe on the “hot” south side of the tree. Boron accumulates in the leaves as they age so symptoms usually appear on older leaves first. Older leaves with high concentrations of boron are relatively short lived compared to trees that have boron at optimum concentrations. Often excessive boron and sodium appear together in leaf tissue analyses.  Boron is associated with a decreased distance between leaf nodes.  Trees with high leaf tissue boron concentrations appear to be less vigorous with shorter branches, probably as a result of the association of boron with decreased distance between leaf nodes. 

Discussion of levels of boron which would be considered excessive in September-sampled spring-flush leaf tissue may be misleading because the particular leaves that are selected for the sample can greatly influence results.  If only leaves with the most severe symptoms are sampled, such as leaves that are mostly yellow with dead margins, concentrations of boron can reach into the thousands of  parts per million (ppm).  A truer picture of the boron status of the grove can be gained by pulling leaves with ‘average’ symptoms. Using this sampling technique, the highest level of boron in orange leaves seen in this office over the past eight years has been 600 ppm from an isolated and particular calcareous part of an orchard located near the town of Edison in Kern County.

Standards from citrus in Florida for the concentration of boron in leaf tissue (4-6 month old leaves on nonfruiting terminals) correlate well with observations made in the San Joaquin Valley as follows:

 

            Deficient         <20

            Low                 21-35

            Optimum         36 - 100

            High                100 - 200

            Excess             > 250

 

Leaf boron concentrations greater than 250 ppm are excessive,  but in older orange, lemon and grapefruit trees visible leaf symptoms are not usually manifested until leaf-tissue boron concentrations exceed  300  ppm.  A range of 300 to 400 ppm show little outward sign of boron toxicity except for some slight tip yellowing and some reduction in vigor.  Excessive defoliation does not usually begin in most citrus until concentrations of approximately 450 ppm are reached. Trees at 450 ppm and greater will, generally, exhibit a thin-canopied, unthrifty, somewhat stunted appearance.  The yield of the tree does not appear to be affected nearly as rapidly as the appearance of the canopy.  At least one large lemon grove in Kern County, that characteristically produces excellent yields of early-maturing, good quality fruit, has elevated leaf-boron levels.  Moderate levels of leaf boron, in the 300 to 400 ppm range in this orchard appear to reduce tree growth, reducing the need to prune, while yield remains relatively unaffected.

Leaf boron concentrations greater than 300 ppm probably warrant further investigation as to the source of the boron.  Orange leaf tissue samples taken from trees planted in the 1960’s or early 1970’s in Kern County routinely show levels of 300 to 400 ppm.  Young trees appear to increase in boron concentration rapidly but at about 300 to 400 ppm the concentration tends to plateau.  Why boron levels tend to plateau is not known.    Chandler pummelos appear to be the most sensitive to excess boron, followed by lemons, grapefruits and oranges.  Leaf boron concentrations of 400 ppm in Chandler pummelos appear to have caused severe stunting of the trees in several orchards in Kern County, while similar levels in Melogold (a pummelo x grapefruit hybrid) resulted in only some tip burn. 

There are actions the grower can take to reduce the amount of boron in the tree.  First the source of the boron should be determined if possible. If boron levels are increasing in the leaf tissue, analyze both surface water and well water.   Avoid using water with greater than 0.5 ppm of boron for irrigation of citrus. Levels of boron that are beneficial to cotton or pistachio can cause severe problems with citrus. Surface water comes from diverse sources in Kern County.  Surface delivered water may have started out as well water, or in some instances as diluted oil-field waste water which may contain relatively high concentrations of boron.   Water districts will know if oil-field waste water is being diluted in irrigation water.  Use of oil-field waste water can be seasonal and irrigation derived in part from oilfields may fluctuate in boron concentration.  If boron is in the water even at slightly elevated levels, avoid spraying it directly on the trees when treating for insect pests or when applying foliar fertilizers.  Fertilizers are foliarly applied because of the quick uptake of dissolved minerals through the leaves.  If boron is in the spray solution, it will be absorbed quickly by the tree along with the potassium, zinc, manganese, nitrogen and other foliar nutrients. Organic matter, manure, composted materials, and mulches on the ground have been shown to reduce boron uptake by the plant from irrigation water with high concentrations of this element.

In the southern San Joaquin Valley, soils should be tested before citrus is planted.   Areas of soil with high boron are found in the most unexpected places.  Boron may have accumulated on some properties when high-boron well water was used before the advent of easier access to water from Sierra snow melt.  

If leaf-tissue boron is high and the water or soil is not, check the foliar fertilizer blends being used.  Often, boron is included in many micronutrient mixes because boron can be deficient in acid soils.  Determine how much boron soil amendments may contain. Pit gypsum can have varying quantities of boron in it.  A ton of this gypsum may contain as much as 20 pounds of boron.

Discovering the cause of high boron in citrus leaves may require an extra soil test in addition to the typical saturated pest extract.   Soil tests for ‘available’ boron using a saturated pest extract can be deceiving.  In many instances where the concentration of boron in a ‘typical’ leaf averaged greater than 300 ppm, plant-available boron in the soil and water frequently averaged less than 0.25 ppm.  However, total soil boron in these same orchards was at very high levels.  Total soil boron estimates both available and unavailable boron. To help determine where the boron in the trees originates, both readily available and total soil boron should be sampled.  This disparity between plant-available and total boron suggests that boron moves between the relatively small plant-available pool in the soil and the much larger ‘unavailable’ pool tied up in these calcareous soils. Soil acidifying agents and acid-forming fertilizers probably increase the availability of boron to citrus trees by making boron that is relatively unavailable to the trees at high pH, more available at lower pH. At any given time, plant-available boron may be relatively low but its constant replacement from the unavailable pool keeps the boron concentration in trees relatively high.  In orchards where total soil boron is elevated; soil pH should probably be kept as high as tree health permits.  Where the total amount of soil boron is moderate and soils are relatively well-drained and topography is flat, acidifying and leaching is probably the preferred option for reducing boron levels. Acidifying the soil and not supplying sufficient water to leach the boron from the root zone can compound the problem by making more boron readily available to the tree.

If boron is not found in the upper soil profile, but is found or suspected to exist deeper,   irrigations could be scheduled that are more frequent but of shorter duration so that most of the citrus roots remain in the upper,  lower-boron portion of the soil profile. 

Actively growing, vigorous trees may dilute the concentration of boron in the leaf tissue through the production of a thick canopy.  Old leaves tend to accumulate boron and drop.  Adequate nitrogen ensures that enough nitrogen is present for production of new leaves.  Increasing the nitrogen fertilization rate can encourage vegetative production and enhance this effect, but too much nitrogen may be associated with adverse fruit quality characteristics like regreening of Valencias, later maturity of early navels or higher yields of smaller fruit.  Keeping other nutrients in the leaf in balance is important if boron is present at excessive concentrations.   Maintaining high concentrations of phosphorous and calcium in the leaves through an appropriate fertilization program should be beneficial as these nutrients have been shown to reduce absorption of boron.

B toxicity
B toxicity

Posted on Sunday, February 24, 2013 at 3:54 PM
  • Author: Craig Kallsen
Tags: B (1), boron (2), citrus (1), toxicity (5)

One, One Hundred, One Thousand

This little mnemonic, or memory aid, in the title is helpful in remembering the critical levels of toxic constituents in irrigation water. The “one” stands for 1 part per million (ppm) of boron (B), the “one hundred” flags 100 ppm of sodium (Na) and chloride (Cl) and the “one thousand” represents the level of total soluble solids (TDS or salts) in water. Levels exceeding the critical values for any of these constituents can present problems for tree growers. The problems typically show themselves as tip-burn and defoliation. The B, Na and Cl are toxic elements at relatively low concentrations, but symptoms appear similar to the damage caused by high salinity.

Water that exceeds the critical levels mentioned in the mnemonic has a greater tendency to cause damage if sufficient leaching is not applied. It doesn’t mean the water is impossible to use, only that greater attention needs to be made to ensure that these salts are adequately leached. High levels of these salts accumulate in the soil with each irrigation. These salts are absorbed by the tree and end up in the leaves where they do damage.

Irrigation is a necessary evil. Every time we apply irrigation water we apply salts, and unless some technique is used to minimize salt accumulation, damage will result. This damage can be more than just leaf drop, but also the stress that induces conditions for root rot. In most years we rely on winter rainfall to correct the salt imbalance resulting from irrigation water.

This year has been a winter largely without rain. Irrigation water was applied throughout the winter, spring, summer and fall and many trees look stressed this spring. Even well irrigated orchards in the spring of 2012 have leaf burn due to the gradual accumulation of salts from irrigation. Avocados, which are generally more sensitive to salts than citrus, drop their salt-burned leaves this spring when flowering begins.

We usually think that it is not necessary to irrigate in the winter, but this winter should change that opinion. To add to the lack of rain problem, it may be necessary to irrigate even if there is rain in the future. The wetted pattern that is created by a drip or microsprinkler emitter also creates a ring of salt in the outer band of the wetted patter. If there is less than an inch of rainfall to push this salt down, this salt tends to diffuse towards the tree where it can accumulate back in the root system. Orchards with even good water quality would find it advisable to run the irrigation system with the first rains. Those with poor water quality definitely should run the microsprinkler system with an equivalent of one-half inch-applied water (13,500 gallons per acre) during or soon after the first events of less than one-half inch rainfall. Growers with water quality exceeding one, hundred, or thousand should be especially alert to the need to manage water in low rainfall winters.

High levels of salts can accumulate in the soil with each irrigation.
Posted on Monday, March 5, 2012 at 9:05 AM
  • Author: Ben Faber
Tags: irrigation (1), nutrients (1), toxicity (5), water (1), water quality (1)
 
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