Salt tolerance of crops

[2] A regional distribution of the 3,230,000 km2 of saline land worldwide is shown in salt affected area based on the FAO/UNESCO Soil Map of the World.

[3] One of the first studies made on soil salinity and plant response was published in the USDA Agriculture Handbook No.

The collection of field data under farmers' conditions was rare, probably due to the greater efforts and higher costs involved, the lack of control of plant growing conditions other than soil salinity, and the larger random variation in crop yields and soil salinity.

For field data with random variation the tolerance level can be found with segmented regression.

Using the logistic sigmoid function for the same data applied in the van Genuchten-Gupta model, the curvature becomes more pronounced and a better fit is obtained.

As a result, the tolerance level (breakpoint, threshold) is larger (4.9 dS/m) than according to the Maas-Hoffman model (3.3 dS/m, see the second figure above with the same data).

The irrigated wheat crop in Egypt has a salt tolerance of ECe=7.6 dS/m beyond which the yield declines. The data were collected in farmers' fields. [ 1 ]
Maas–Hoffman model for wheat production and soil salinity in farmland. The salt tolerance (breakpoint, threshold) is about ECe = 3.3 dS/m
Van Genuchten–Gupta model for carrot production and soil salinity in the field
Logistic sigmoid model for carrot production and soil salinity in the field [ 12 ]
Partial regression is used to detect the maximum range of no influence in wheat fields. Tolerance is about ECe=5 dS/m