Management of Salt-Affected Soils - Practices of Irrigation and On-farm Water Management - page 299

Use of saline water in agriculture requires the following principal changes from
standard irrigation practices:

(i) Selection of appropriate salt tolerant crops
(ii) Improvements in the water management, and in some cases, the adoption of
advanced irrigation technology (such as drip, sprinkler, subirrigation)
(iii) Maintenance of soil physical properties to assure soil tilth and adequate soil
permeability to meet crop water and leaching requirements.

Irrigation with saline water may cause some degree of salinization of the soil.
This will cause a decrease in crop yield relative to yield under nonsaline conditions.
Relative yields decrease with increasing salinity of the irrigation water.

8.5.4 Yield Reduction Due to Salinity

Relative yield ( Y r , in percent) at any given soil salinity (EC) above the threshold
level can be calculated by the following straight line equation (adapted from Ayers
and Westcot, 1985 ) :

EC 0 − EC e

Y r = 100 × (8.3)

EC 0 − EC 100

where

Y r = Relative yield, in percent

EC 0 =

EC of soil at zero yield (i.e., EC e where Y = 0) (dS/m)

EC e electrical conductivity (EC) of the soil saturation extract (dS/m) in

question
EC 100 =

=

the salinity threshold level above which the crop yield starts to decline
(maximum soil salinity level at 100% yield potential, i.e., the upper EC e
where Y r =

100)

The values of EC 100 and EC o for a given crop can be taken from the literature or
appropriate figure or table.
The actual yield,

Y act = Y r × Y p (8.4)

where Y p is the potential yield under nonsaline condition.
A piece-wise linear model can be established from the principle of the Eq. (8.3):

Y r = 100, 0 < EC e ≤ EC t (8.5a)

Y r = S (EC e − EC t ), EC t <EC e ≤ EC 0 (8.5b)

Y r = 0, EC e >EC 0 (8.5c)