Q&A: Evaluating a Water Supply for Suitability to Irrigate Nut Crops

After receiving the results of a water analysis, there are several components that need to be reviewed to determine suitability of the water for the planted crop. If the water does not meet the expected suitability range, it may require ammendments (e.g. gypsum or acid) or mixing with other water sources to prevent crop loss. Below are five questions that are usually asked when reviewing a water sample as well as some other information regarding a water analysis and conversions.

  1. Does the salt concentration (ECw) pose a potential problem (osmotic effects)?
 Crop  Unit Degree of growth or yield reduction
None Increasing Severe
Almond and Walnut dS/m <1.1 1.1 -3.2 >3.2
Pistachio dS/m <4.0 4.0 – 8.0 >8.0
  1. Are there specific elements (B, Cl, and Na) that could accumulate to potentially toxic levels?
 Element  Unit  Crop Degree of growth or yield reduction
None Increasing Severe
B (boron) mg/l (ppm) Almond and Walnut <0.5 0.5 – 3.0 >3.0
Pistachio <4.0 4.0 – 10 >10.0
Cl (chloride) meq/l Almond and Walnut <4.0 4.0 – 10 >10.0
Pistachio <20.0 20 – 40 >40.0
Na (sodium) SAR(none) Almond and Walnut <3.0 3.0 – 9.0 >9.0
Pistachio <5.0 5.0 – 10 >10.0
Na (sodium) meq/l Almond and Walnut <4.0 4.0 – 7.0 >7.0
Pistachio <20.0 20 – 40 >40.0
  1. Could the water chemistry contribute to unstable surface soil structure and lower water infiltration rates?
 Lab Information  Unit Potential of Water Infiltration Problems Developing
Unlikely Increasing Likelihood Likely
Ratio of SAR/ECw ratio <5.0 5.0 – 10.0 >10
Ratio Ca/Mg ratio >2.0 2.0 – 1.0 <1.0
  1. Could the water chemistry be prone to plugging drip emitters, microsprinklers, or filters?
 Lab Information  Unit Potential for Water Infiltration Problems Developing
Unlikely Increasing Likelihood Likely
ECw dS/m <0.8 0.8 to 3.0 >3.0
HCO3+CO3 meq/l <2.0 2.0 – 4.0 >4.0
Mn (manganese) mg/l <0.1 0.1 – 1.5 >1.5
Fe (iron) mg/l <0.2 0.1 – 1.5 >1.5

5. How much nitrate-nitrogen is in these irrigation water supplies?

NO3-N (mg/l, ppm) x 2.7 = lbs N per acre-foot of water

NO3 (mg/l, ppm) x 0.6 = lbs N per acre-foot of water             

 

LABORATORY DETERMINATIONS AND UNITS FOR EVALUATING IRRIGATION WATER

Test Symbol Unit
Electrical Conductivity ECw dS/m or mmhos/cm
Total Dissolved Solids TDS mg/l (ppm)
Calcium Ca meq/l
Magnesium Mg meq/l
Sodium Na meq/l
Sodium Adsorption Ratio SAR none
Adjusted Sodium Adsorption Ratio SARadj none
Chloride Cl meq/l
Sulfate SO4 meq/l
Bicarbonate HCO3 meq/l
Carbonate CO3 meq/l
Acidity/Alkalinity pH none
Boron B mg/l (ppm)
Nitrate-nitrogen NO3-N mg/l (ppm)
Manganese Mn mg/l (ppm)
Iron Fe mg/l (ppm)

 

CONVERSION FACTORS FROM MILLIGRAMS PER LITER (mg/l or ppm) to MILLIEQUIVALENTS PER LITER (meq/l).

 Cation/Anion  Symbol Conversion Factor
Bicarbonate HCO3 61
Calcium Ca 20
Carbonate CO3 30
Chloride Cl 35
Magnesium Mg 12
Sodium Na 23
Sulfate SO4 48
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2 thoughts on “Q&A: Evaluating a Water Supply for Suitability to Irrigate Nut Crops


    1. EC is the generalized abbreviation for electrical conductivity, while ECw indicates the electrical conductivity of water. I might have just used EC when describing water. I will work through to correct that.

      David


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