Top Five Questions: Evaluating a Water Supply for Suitability to Irrigate Nut Crops

  • Does the salt concentration (ECw) pose a potential problem (osmotic effects)?

Degree of Growth or Yield Reduction
Crop Unit None Increasing Severe
Almond, Walnut & Prune dS/m < 1.1 1.1 - 3.2 > 3.2
Pistachio dS/m < 4.0 4.0 - 8.0 > 8.0

 

  • Are there specific elements (B, Cl, and Na) that could accumulate in the tree or soil to potentially toxic levels?

Degree of Growth or Yield Reduction
Element Unit Crop None Increasing Severe
B (boron) mg/l (ppm) Almond, Walnut, & Prune <0.5 0.5 - 3.0 >3.0
Pistachio <4.0 4.0 - 10 >10.0
Cl (chloride) meq/l Almond, Walnut, & Prune <4.0 4.0 - 10 >10.0
Pistachio <20.0 20 - 40 >40.0
Na (sodium) SAR (none) Almond, Walnut, & Prune <3.0 3.0 - 9.0 >9.0
Pistachio <5.0 5.0 - 10 >10.0
Na (sodium) meq/l Almond, Walnut, & Prune <4.0 4.0 - 7.0 >7.0
Pistachio <20.0 20 - 40 >40.0

 

  • Could the water chemistry reduce soil tilth, porosity, and cause slower water infiltration rates?

Potential of Water Infiltration Problems Developing
Lab Information Unit Unlikely Increasing Likelihood Likely
Ratio of SAR/ECw ratio <5.0 5.0- 10.0 >10
Ratio Ca/Mg ratio < 4.0 2.0- 1.0 <1.0

 

  • Could the water chemistry be prone to plugging drip emitters, microsprinklers, or filters and reduce irrigation distribution uniformity?

Potential for Plugging Problems Developing
Lab Information Unit 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

 

  • How much nitrate-nitrogen is in an irrigation water supply?

If lab reports NO3-N, then:
NO3-N (mg/l, ppm) x 2.7 = lbs N per acre-foot of water

If lab reports NO3, then:
NO3 (mb/l, ppm) x 0.6 = lbs N per acre-foot of water

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