The effect of salt precipitation and high sodium concentrations on soil hydraulic conductivity and water retention

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Abstract
Controlled irrigation management of moderate to poor quality water must assure sufficient movement of solution through the root zone to maintain a salinity regime which a crop can tolerate while at the same time minimizing the deterioration of groundwater or river quality. One proposal for accomplishing this objective is a policy of high‐frequency irrigation and minimum leaching, which encourages precipitation of calcium salts from solution and hence decreases the salt flux below the root zone. However, the concentration and fraction of sodium in the remaining solution are increased by such a policy and could be harmful to soil or plant properties. The work reported here analyzes the major plant‐soil‐salinity interactions resulting from irrigation with saline water at controlled leaching fractions. Simulations are run for leaching fractions of 0.30, 0.05, and 0.01 and three different water uptake patterns for two high‐sulfate waters with different salinity levels: 2.1 and 6.6 mmho/cm. Results suggest that soil hydraulic conductivity and water retention should not be adversely affected by high sodium levels or cumulative salt precipitation even at very low leaching fractions. However, it is probable that plant activity will be impaired by the lower leaching fractions because of high osmotic pressure within the root zone and that root proliferation could be reduced by soil structure cementation resulting from salt precipitation.