Water Stress Effects on Salt Movement

The effect of irrigation water stress that is already seen in some parts the world as a result of water shortage and it will surely be employed in near future in most part of the world due to global warming effects is investigated in this study. The calibrated and validated salt transport model, in order to see the effects of the water stress on salt transport, is applied to a 1992 study of Robinson et al. at the Desert Research and Extension Center, University of California, in the Imperial Valley of California. Table 22.4 presents four different irrigation treatment - optimum check, minimum stress, short stress, and long stress. The irrigation water which is diverted from Colorado River into All American Canal had an average ECw of 1.25 dS/m (850 mg/L) about twice of the one used at the Fruite Research Center, CO. The soil in the Imperial Valley is Holtville clay extending 60-90 cm in depth overlying sandy clay. The observed ECe in 1991 was assumed as initial ECe values.

Table 22.5 summarizes observed versus predicted salt concentrations along the soil depth of 120 cm. The measured salt concentration data clearly show that under stress conditions, salt concentration increases along the soil depth in time. For example, in between 60 and 120 cm zone, on the average, the measured ECe on October 16, 1991 was around 6.08 dS/m under optimum conditions, it then became 6.93 under minimum stress, 8.38 under short stress, and 9.88 dS/m under long stress conditions. The salt concentration increase is, on the average, 14%, 38%, and 63% under minimum, short, and long stress conditions, respectively. The results in the table show that the developed salt transport model shows good performance in predicting concentrations under optimum and minimum stress conditions along the soil depth. Under short and long stress conditions, the model performs poorly in predicting salt concentrations especially in the lower zone. The computed error measures, on the average, for the results in Table 22.5 are MAE = 1.15 dS/m and MRE = 25.4%.

Table 22.4 Water stress irrigation treatments in 1991 in the Imperial Valley, CA Number of total applied type irrigations water

Treatment type July

August

September

October

Optimum 3

2

2

2

1,269

Minimum stress 3

1

1

2

1,203

Short stress 3

0

0

2

991

Long stress 0

0

0

2

821

Table 22.5 Measured versus predicted ECe values under four different

stress conditions

Soil layer

Measured

Predicted

Date

depth (cm)

ECe (dS/m)

(dS/m)

Optimum treatment

June 4, 1986

30.0

2.60

4.10

60.0

3.30

3.95

90.0

6.40

5.75

120.0

5.85

5.70

September 4, 1986

30.0

2.90

4.85

60.0

3.40

4.40

90.0

6.95

5.75

120.0

5.90

5.70

October 16, 1986

30.0

3.20

5.05

60.0

3.45

4.55

90.0

6.30

6.90

120.0

5.85

5.70

Minimum stress treatment

June 4, 1986

30.0

2.30

3.55

60.0

3.20

3.45

90.0

6.30

6.55

120.0

6.90

7.10

September 4, 1986

30.0

2.55

4.10

60.0

3.90

3.80

90.0

6.60

6.60

120.0

6.85

7.10

October 16, 1986

30.0

2.65

4.55

60.0

4.55

4.00

90.0

7.45

6.60

120.0

6.40

7.00

Short stress treatment

June 4, 1986

30.0

2.55

4.10

60.0

4.75

4.35

90.0

7.05

6.10

120.0

6.10

6.30

September 4, 1986

30.0

2.80

4.15

60.0

5.40

4.45

90.0

8.70

6.00

120.0

5.75

6.10

(continued)

Table 22.5 (continued)

Soil layer

Measured

Predicted

Date

depth (cm)

ECe (dS/m)

(dS/m)

October 16, 1986

30.0

3.00

5.00

60.0

5.50

4.35

90.0

10.20

6.00

120.0

6.55

6.20

Long stress treatment

June 4, 1986

30.0

2.20

3.68

60.0

3.20

3.70

90.0

5.65

5.45

120.0

6.30

6.32

September 4, 1986

30.0

2.45

3.55

60.0

3.75

3.70

90.0

9.25

4.74

120.0

8.95

6.25

October 16, 1986

30.0

2.75

4.05

60.0

4.05

3.80

90.0

10.80

5.20

120.0

8.95

6.50

0 0

Post a comment