Salt movement, leaching efficiency, and leaching requirement

Abstract

To study the salt movement in a soil profile, experiments were conducted on sandy loam and silty clay loam in tanks. The chloride concentration and electrical conductivity of the soil water were found from soil water samplers and salinity sensors. The standard deviation of the chloride concentration at each depth was small at the beginning of the percolation process when the soil was uniformly non-saline or highly saline; it increased strongly during the process and returned to its original value at the end. This points to a very heterogeneous water and salt movement through the soil profile. The chloride concentration, when increasing or decreasing rapidly, shows a large scattering. The effective mixing length in the tank experiments appears to be much greater than in laboratory soil columns. It varies between 10 and 15 cm in sandy loam and between 15 and 30 cm in silty clay loam. Irrigation water and soil moisture do not mix completely. An increasing part of the irrigation water moves through the soil without contributing to the leaching process. The results of the tank experiments agree with those of field experiments on similar soils. The consequences for the calculation of the leaching requirement in practice are discussed.