Effect of amount of water applied and application rate on solute leaching from porous media

摘要

In the last decades many experiments were conducted to study the leaching of salts from soils. The results lead to the following hypotheses about the effect of the amount of water applied and the application rate on the leaching of solutes from soils: Small pores contain more solutes than large ones. Hence, even at low application rates, when water flows only through small pores, large amounts of solutes are leached out of a soil. Raising the application rate and thereby increasing the size of thepores involved in flow will not lead to a proportional increase in the solute load. If the application rate is kept constant, the solute concentration in the drainage water decreases with the amount of water applied. Each additional unit of water leads to smaller increases in the total solute load. A given amount of water applied at a low rate (and hence over a longer time) leaches more solutes than the same amount applied at a higher rate, i.e. over a shorter time. These hypotheses were examined in laboratory experiments and found to be valid. For practical purposes this means that it is not the amount of water, but the rate at which it is applied, which mainly determines the amount of solutes leached. The lower the rate, the more can be leached witha given volume of water. Leaching is therefore more effective at lower application rates, which result in lower soil water contents, than at higher ones, which result in higher water contents. Furthermore, solute concentrations in the drainage water arehigher at lower application rates.