NEWSLETTER ARTICLES

Vegetables and Plant Pathology


From our Central Coast Agriculture Highlights newsletter
April 1997 issue:

VEGETABLE CROPS SALT TOLERANCE
by Khaled M. Bali, Farm Advisor for Soils and Water, Imperial County

Salts present in the soil-water system can reduce crop yield and cause decline in quality. Most vegetable crops are sensitive to salinity. Salinity can affect crop growth through specific-ion toxicities and osmotic effects. Specific-ion toxicity occurs when the concentration of one ion is high enough to cause injury in a plant. Boron, chloride, and sodium are a few of the ions that impede plant growth and development. Specific-ion toxicity causes leaf burn on the tips and margins of crop leaves. Osmotic effects also result in decline in yield and quality due to the movement of water from the cells of plant root to the soil-water system outside the roots. At normal salinity levels, water moves from the soil-water system to plant roots because of the higher concentration of constituents in the root cells. Soil salinity is commonly expressed in dS/m (1 dS/m is equivalent to 1 mmhos/cm). The effect of overall soil salinity on vegetable crop yield can be described by the following equation:

Y = 100-B(ECe-A)

where Y is the relative yield. A is the threshold value (dS/m) or the maximum root salinity at which no reduction in yield is observed. B is % reduction in yield due to 1 unit increase in salinity over the threshold value, and ECe is the average root zone salinity. Soil salinity levels below the threshold values will not affect crop yield or quality. Values of A and B for various vegetable crops are presented in Table 1. The following example illustrates the use of the above equation:

Examples: Average root zone salinity = 3 dS/m Crop: Lettuce, and from Table 1 A = 1.3, B = 13.0 Y = 100-13.0(3-1.3)=77.9%

Crop: Tomato, and from Table 1 A = 2.5, B = 9.9 Y = 100-9.9(3-2.5) = 95.5%

Table 1.
CropThreshold Salinity (A)(B)Tolerance Level
Asparagus
4.1
2.0
T
Bean
1.0
19.0
S
Broccoli
2.8
9.2
MS
Carrot
1.0
14.0
S
Celery
1.8
6.2
MS
Lettuce
1.3
13.0
S
Onion
1.2
16.0
S
Pepper
1.5
14.0
MS
Potato
1.7
12.0
MS
Radish
1.2
13.0
MS
Spinach
2.0
7.6
MS
Tomato
2.5
9.9
MS

A=Threshold value in dS/m B=%reduction in yield per unit increase in salinity greater than the threshold value S=sensitive MS=moderately sensitive T= tolerant Source: B. R. Hanson and S. R. Grattan. 1992. Agricultural Salinity and Drainage: A User’s Guide Handbook. University of California, Davis.

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