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

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Posted on October 3 2017 by Allan Fulton

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

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
B (boron)	mg/l (ppm)			Pistachio	<4.0	4.0 - 10	>10.0
Cl (chloride)	meq/l	Almond, Walnut, & Prune	<4.0	4.0 - 10	>10.0
Cl (chloride)	meq/l			Pistachio	<20.0	20 - 40	>40.0
Na (sodium)	SAR (none)	Almond, Walnut, & Prune	<3.0	3.0 - 9.0	>9.0
Na (sodium)	SAR (none)			Pistachio	<5.0	5.0 - 10	>10.0
Na (sodium)	meq/l	Almond, Walnut, & Prune	<4.0	4.0 - 7.0	>7.0
Na (sodium)	meq/l			Pistachio	<20.0	20 - 40	>40.0

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

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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