WSP08301

• File Number: 8273.100.50
• Description: Colorado River Basin Salinity Control - Federal Agency Reports - BOR
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 2/1/1988
• Title: Estimating Economic Impacts of Salinity of the Colorado River - Final Report - February 1988
• Water Supply Pro - Doc Type: Report/Study

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chapter 3
ECONOMIC DAMAGES
TO IRRIGATED AGRICULTURE

Salinity Damage Threshold of
Crops

The salt tolerance level of plants - both food
crop and ornamental- varies greatly according
to a number of conditions of which the level of
salinity in irrigation water is but one. Climate,
farming practices, soil conditions, and the constit-
uent makeup of minerals in irrigation and soil
water all contribute to the tolerance, or lack of
tolerance, of most commonly farmed crops to
the presence of salt. In this study the primary
interest is in the effect of the TDS level of
Colorado River irrigation water on crop yields.
E.V. Maas, Research Leader at the U.S. Salinity
Laboratory in Riverside, California, has devoted
a career to examining the salt tolerance of crops.
His latest work, published in 1986, updates the
results of more than 20 years of study and
provides us with relative guidelines on the
tolerance of crops to differing degrees of soil
salinity as measured in deciSiemens/meter
(dS/m) of electrical conductivity of saturated soil
extract. Maas cautions that "soil salinity is sel-
dom constant with time or uniform in space."
But, he adds that the most recent evidence indi-
cates that the critical area is, for areas of fre-
quent irrigation, the upper part of the root zone
where "soil salinity is influenced mostly by the
salinity of the irrigation water." His salt
tolerance tables arc prepared for this upper
zone at the threshold level above which "yield
decreases approximately linearly as salinity
increases."

Keeping Maas' caution in mind that thresh-
old salinity levels are only approximate because
growing conditions can vary so dramatically, it is
possible to convert the levels of soil electrical

conductivity to TDS levels in irrigation water by
using a formula presented in Irrigatioll with
Reclaimed MUlIicipal Wastewater.9 In that
formula, TDS is empirically related to electrical
conductivity of the saturation extract (repre-
sented as dS/m) multiplied by 640. The electri-
cal conductivity (salinity level) of the irrigation
water, as it relates to soil saturation, can be
determined by dividing the soil saturation level
of TDS by 1.5. (For example, if the soil extract
threshold level of carrots is 1.0 dS/m, multiply
the 1.0 x 640 to convert to TDS and divide the
rcsult [640 in this case] by 1.5 to obtain the TDS
equivalent for irrigation water of 427 mg/L.)
Thus the threshold levels for TDS in applied
irrigation water, as identified by Maas, are
shown in table 5.

Table 5. - TDS threshold levels
in applied irrigation water
Source: Maas
Qrop IllS. Qrop IllS.
Lettuce 555 Alfalfa 853
Cotton Lint 3285 Grapes, table 640
Carrots 427 Cantaloupe 1422
Wheat 2560 Dates 1707
Oranges 725 Sugar Beets 2987
Grapefruit 768 Lemons 768
Onions 512 Beans 427
Corn 726 Cabbage 768
Celery 768 Peppers 640
Potatoes 725 Spinach 853
Strawberries 427 Sweet Potato 640
Almonds 640 Berries/Plums 640
Peaches 725 Avocados 427

9Univcrsity of .California, Davis. Department of Land, Air and Wafer Resources. Irrill'::llinn with Reclaimed Municip(l]
WtlslCYnlfer" ^ (jUlrlnnl"e M<lnual Sacramento: State Waler Resources Control Board July 1984 Ap end" H H?
, ,P IX ,page -_.

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