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The soil salinity on the x-axis is represented by electric conductivity (ECe). In this example the crop has a salt tolerance (threshold) of ECe = Pb = 7 dS/m beyond which the yield diminishes. The Maas–Hoffman model is a mathematical tool to characterize the relation between crop production and soil salinity.
For example, assuming irrigation water with a low salt concentration of 0.3 g/L (equal to 0.3 kg/m 3 corresponding to an electric conductivity of about 0.5 FdS/m) and a modest annual supply of irrigation water of 10,000 m 3 /ha (almost 3 mm/day) brings 3,000 kg salt/ha each year.
Soil salinity is the salt content in the soil; the process of increasing the salt content is known as salinization. [1] Salts occur naturally within soils and water. Salination can be caused by natural processes such as mineral weathering or by the gradual withdrawal of an ocean.
The thermal conductivity is sometimes a constant, otherwise an average value of conductivity for the soil condition between the surface and the point at depth is used. δ T {\displaystyle \delta T} is the temperature difference ( temperature gradient ) between the two points in the soil between which the heat flux density is to be calculated.
A river or lake water with a salinity of around 70 mg/L will typically have a specific conductivity at 25 °C of between 80 and 130 μS/cm. The actual ratio depends on the ions present. [14] The actual conductivity usually changes by about 2% per degree Celsius, so the measured conductivity at 5 °C might only be in the range of 50–80 μS/cm.
Table of saturated hydraulic conductivity (K) values found in nature. a table showing ranges of values of hydraulic conductivity and permeability for various geological materials. Values are for typical fresh groundwater conditions — using standard values of viscosity and specific gravity for water at 20 °C and 1 atm.
The salt level is often taken as the soil salinity or the salinity of the irrigation water. Salt tolerance is of importance in irrigated lands in (semi)arid regions where the soil salinity problem can be extensive as a result of the salinization occurring here. It concerns hundreds of millions of hectares. [2]
The range of EC values is obtained by mixing fresh water with the appropriate amount of seawater having a salinity corresponding to an EC value of about 50 dS/m. After planting, crops were allowed to germinate under fresh water conditions before the salt treatment started.