Fruit & Nut Research and Information Center
Fruit & Nut Research and Information Center
Fruit & Nut Research and Information Center
University of California
Fruit & Nut Research and Information Center

Salinity Problems


Salinity Evaluation

Soils and irrigation water contain dissolved salts, which affect water penetration and uptake, serve as plant nutrients, and may be phytotoxic in high concentrations. Assessment of salinity conditions is generally based on soil and water lab analyses, although knowledge of the cropping history of the orchard is useful. The discussion here focuses on aspects of Lab Reports for irrigation water and soil-water, specific to salinity: pH, EC, ion measurements, and SAR, and management options.

Soil & Water

Source

Sanden, Blake, Allan E. Fulton amd Louise Ferguson. Managing Salinity, Soil and Water Amendments. (UC Cooperative Extension Kern County) Retrieved Jan. 26, 2012.

pH: measures Acidity or Alkalinity of water based on hydrogen ion (H+) activity. A neutral pH is 7.0; acidic is pH < 7.0, alkaline is pH > 7.0. pH figures in the selection of soil amendments.

Electrical Conductivity (EC): of water is a reflection of total salinity, and is based on the presence of the charged ions discussed below.

  • EC, designated as ECe (for soil-water) and ECw (for irrigation water), is measured in dS/m.
  • Excess salinity (high EC) in the root zone reduces the amount of water the tree can absorb, so a tree may show symptoms of water stress, even though irrigation seems adequate.
  • Excess salinity decreases rates of evapotranspiration, which in turn, affects shoot growth, crop yield and quality.

Decades of research have established correlations between EC values and yield in many crops (Table 1). These serve as a guideline; variable factors such as tree age, rootstock, and length of time have a role. The leaching fraction (LF) is an additional quantity of water above crop requirements, to leach salts from the root zone. Note that the LF is given in the footnotes in Table 1.

Table 1. Critical Levels of Salinity (EC) Indicating Effect on Yield

Young Walnut 1/ EC (dS/m) No Effect Increasing Severe Effect
Avg. Root Zone
(soil-water sample)
ECe 1.5 1.5 - 4.8 >4.8
Irrigation Water
(water sample)
ECw 1.1 1.1 - 3.2 >4.8
Mature Almond 2/        
Avg. Root Zone ECe 1.5 1.1 - 3.2 >4.8
Irrigation Water ECw 1.1 1.1 - 3.2 >4.8
Mature Pistachio 3/        
Avg. Root Zone ECe <6 6 - 8 >8 - 12
Irrigation Water ECw <4 4 - 8 >8 - 12
Plums, Peaches, Nectarines 4/        
Avg. Root Zone ECe 1.5 2.0 - 3.0 >4.0
Irrigation Water ECw 1.0 1.3 - 3.0 >4.0

Leaching fractions: 1/all levels: 15%; 2/all levels: 15%; 3/ No effect: 10-20%, Increasing: 10-20%, Severe: 20-40%
Source: 1/Walnut Production Manual; 2/Almond Production Manual; 3/Pistachio Production Manual; 4/Peaches, Plums, Nectarines: Growing & Handling for Fresh Market

Ion Measurements: specifically, the charged ions: cations and anions. The concentration of ions is measured in meq/L. The meq/L value can be converted to mg/L using a conversion factor to calculate soil amendment quantities (link to Lab Reports table).The ions which contribute to salinity are:

  • Positively charged cations: Calcium Ca++, Sodium Na+, Magnesium Mg++, Potassium K+
  • Negatively charged anions Bicarbonate HCO3, Carbonate CO3=, Sulfate SO4= , Cloride Cl-

Specific Salts Sodium Na+, Cloride Cl- and Boron B: The level of these ions is typically monitored because they can accumulate to toxic levels in the trees, causing tissue death at leaf margins and tips. It can be difficult to distinguish these specific toxicities from general salinity toxicity.

Sodium Absorption Ratio (SAR): evaluates Sodium problems, it is a ratio of soluble cations: Na+ to Ca++ and Mg++

SAR adj: The SAR is more useful than the Na+ value alone, because more Na+ can be tolerated when Ca++ and Na+ increase proportionally. SARadj takes the levels of HCO3 and CO3= into account, because these anions take Ca++ from the soil to form lime, thus increasing the ratio of Na+ to Ca++. Water higher in these anions has an SARadj higher than the SAR. SAR is for irrigation water only, and is reported as a number with no unit of measurement.
add ESP

Tables 2, 3 and 4 present critical levels of Na+, Cl- and B for the root zone (soil-water), irrigation water, and leaf tissue. Close monitoring of all three is useful in evaluating salinity.

Table 2. Critical Levels of Sodium (Na+) Ions

Walnut 1/ Unit No Effect Increasing Severe Effect
Avg. Root Zone SAR <5.0 5 - 15 >15
Irrigation Water SAR <3.0 3 - 9 >9
Leaf Tissue % <0.10 0.10 - 0.30 >0.30
Almond 2/        
Avg. Root Zone ESP <5.0 5 - 15 >15
Irrigation Water SAR <3.0 3 - 9 >9
Leaf Tissue % <0.25 0.25 - 0.40 >0.4
Pistachio 3/        
Avg. Root Zone        
Irrigation Water        
Leaf Tissue (Jul-Aug) ppm <300 300 - 700 >800
Peaches, Plums, Nectarines 4/        
Avg. Root Zone ESP <1.0 5 - 10 >10
Irrigation Water SARadj <3.0 3 - 9 >9
Leaf Tissue ppm      

Source: 1/Walnut Production Manual; 2/Almond Production Manual; 3/Pistachio Production Manual; 4/Peaches, Plums, Nectarines: Growing & Handling for Fresh Market

Table 3. Critical Levels of Cloride (Cl-) Ions

Walnut 1/ Unit No Effect Increasing Severe Effect
Avg. Root Zone meq/L <5.0 5 - 10 >10
Irrigation Water meq/L <5.0 5 - 10 >10
Leaf Tissue ppm <0.30 0.30 - 0.50 >0.50
Almond 2/        
Avg. Root Zone meq/L <5.0 5 - 15 >15
Irrigation Water meq/L <4.0 4 - 10 >10
Leaf Tissue % <0.3 0.3 - 0.5 >0.5
Pistachio 3/        
Avg. Root Zone        
Irrigation Water        
Leaf Tissue (Jul-Aug) % <0.2 0.2 - 0.4 >0.4
Peaches, Plums, Nectarines 4/        
Avg. Root Zone meq/L <5.0 5 - 15 >15
Irrigation Water meq/L <4.0 4 - 10 >10
Leaf Tissue        

Source: 1/Walnut Production Manual; 2/Almond Production Manual; 3/Pistachio Production Manual; 4/Peaches, Plums, Nectarines: Growing & Handling for Fresh Market

Table 4. Critical Levels of Boron (B) Ions

Walnut 1/ Unit No Effect Increasing Severe Effect
Avg. Root Zone mg/L <0.5 0.5 - 3.0 >3.0
Irrigation Water mg/L <0.5 0.5 - 3.0 >3.0
Leaf Tissue ppm <36 36 - 200 >200
Almond 2/        
Avg. Root Zone mg/L <0.5 0.5 - 3.0 >3.0
Irrigation Water mg/L <0.5 0.5 - 3.0 >3.0
Leaf Tissue ppm <30 30 - 85 >85
Pistachio 3/        
Avg. Root Zone        
Irrigation Water        
Leaf Tissue (Jul-Aug) ppm <300 300 - 700 >800
Peaches, Plums, Nectarines 4/        
Avg. Root Zone ppm <1.0 1.0 - 4.0 >4.0
Irrigation Water mg/L <0.7 0.7 - 3.0 >3.0
Leaf Tissue        

Source: 1/Walnut Production Manual; 2/Almond Production Manual; 3/Pistachio Production Manual; 4/Peaches, Plums, Nectarines: Growing & Handling for Fresh Market

Nitrate-Nitrogen: Nitrate toxicity (NO3-) is a concern when too much nitrogen fertilizer is applied. Lab typically report nitrogen in water and soil samples as the amount of nitrate (NO3- - N). Table 5 lists critical levels for nitrate. For irrigation water, the unit of measure is mg/L; note that soil nitrate is typically reported as ppm in dry soil, NOT the concentration in soil-water. The value is for a composite of soil samples taken to depth of 1 ft.

Table 5. Critical Levels of Nitrate - Nitrogen (NO3- - N)

  Unit Low Moderate High
Avg. Root Zone Soil
Depth to 1 ft.
ppm 0 - 10 10 - 20 >20
Irrigation Water mg/L 0 - 3 3 - 10 >10

Source: 3/Pistachio Production Manual

It is useful to convert these values to pounds per acre-foot, in order to factor in this N when planning fertilization treatments:

Conversion for irrigation water analysis (there are 2.7 million lbs of water per ac-ft:

  • Conversion: mg/l of nitrate*2.7 = sample pounds/acre-ft of N
  • Example: 2.3 mg/l of nitrate*2.7 = 6.2 pounds/acre-ft of N

Conversion for soil analysis (there are 4 millions lbs of soil per ac-ft):

  • Conversion: ppm of nitrate*4 = sample pounds/acre-ft of N
  • Example: 9.7 mg/l of nitrate*4 = 38.8 pounds/acre-ft of N?

References

Louise Ferguson (ed.) Pistachio Production Manual. 2008.  UC Fruit & Nut Research and Information Center, University of California, Davis. 276 pp.

Warren Micke (ed.) Almond Production Manual. 1996. Agriculture and Natural Resources, University of California. 296 pp.

David Ramos (ed.) Walnut Production Manual. 1997. Agriculture and Natural Resources, University of California. 328 pp.

LaRue, James H. and R. Scott Johnson. 1989. Peaches, Plums, Nectarines: Growing & Handling for Fresh Market. UC Postharvest Technology Center, University of California, Davis. 252 pp.

Page Last Updated: January 26, 2012
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