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SALINITY-L  February 1999

SALINITY-L February 1999

Subject:

saline/sodic groundwater

From:

"J.D.(Jim) Oster" <[log in to unmask]>

Reply-To:

Salinity-L Discussion List <[log in to unmask]>

Date:

Thu, 11 Feb 1999 09:31:07 -0800

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (89 lines)

I would not recommend using this water. Others may disagree.

This should be the start of several exchanges. There is extensive research
related to it and one can pose management strategies that may allow its use
-- but each soil is different, each farmer brings different skills to the
situation, availability of amendments pose constraints, crop response will
vary depending on crop tolerance and climatic conditions, but the possible
impacts of rain poses the greatest challenge to assess.

The following analysis was provided.

pH 8.3; EC 2.7dS/me; TotalAlk to pH4.5
790mg/l; Na570mg/l; Ca7.0; Cl 370; and Mg9.8 giving an adjRNa = 39.

I do the following as the first step of a water quality assessment. It
basically is a Q/C check of the analytical data and converts mass
concentrations to charge concentrations. The latter are useful in that they
provide a simple means to do a quality control check as EC and charge
concentrations are closely related, and positive charge concentrations must
equal negative charge concentrations.

As a somewhat humorous asside, roots don't weight salts they count them.

HCO3 = 790/61 = 13.0 mmolc/L
Cl = 370/35.5 = 10.4 mmolc/L
        total  =  23.4 mmolc/L

Na = 570/23 = 24.8 mmolc/L
Ca = 7.0/20 = 0.4 mmolc/L
Mg = 9.9/12.2 = 0.80 mmolc/L
        total = 26.0 mmolc/l
SAR = 32.0
adjRna (Ayars and Westcot, 1985) = 34.4

26 mmolc/L divided by 2.7 dS/m = 9.6 (mmolc.m)/(L.dS). This ratio is
reasonable.

Since charge concentrations of cations and anions should be equal, sulfate
or nitrate may make up the difference.

Lime will do little to change the SAR of the water as is evident from the
adjRna value being greater than the SAR of the water. The water is not able
to dissolve calcite, or soil lime. Calcite will not be very soluble during
the rainfall season unless it is mixed into the soil and the soil pH is
acidic. The high SAR of the water could cause an acidic soil to become
quite alkaline -- much would depend on the level of acidity in the first
place and how much  groundwater infiltrated into the soil.

Infiltration during the rainfall season could be nil because rain would be
expected to lower the soil salinity in the soil surface without changing
the exchangeable sodium levels. An ESP of 3 can cause problems when the
salinity is near zero and the soil surface is bare; an ESP of 30 or higher
would almost certainly cause problems unless it is stabilized by an
extensive, shallow, fibrous root system.

Consider the implications of the following data which can be found on p48
of USDA hndbk 60:

CaCO3 solubility as a function of pH.

pH of a CACO3 saturated solution           Solubility of CaCO3
                                                mmolc/L
6.2                                                     19.3
6.5                                                     14.4
7.1                                                     7.1
7.8                                                     2.7
8.6                                                     1.1
9.2                                                     0.8
10.1                                                    0.4

Obviously, the solubility of calcite will be too at pH's greater than 7.8
to be effective replacing exchangeable sodium or raising the salinity of
the soil solution.

Would I recommend using this water, based on the information provided?

No.


J.D. Oster, Soil and Water Specialist and Adjunct Professor,
Winter/Spring Office: Department of Env. Sci.,
University of California, Riverside, CA 92521. 909-787-5100

Summer/Fall Office: 32 Wishram Tr., Graeagle Ca.
P.O. Box 1344, Graeagle, Ca. 96103. 530-836-1835
Webpage: http://esce.ucr.edu - home of Soil Physical
Chemistry Notes.

e-mail: [log in to unmask]

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