Optimum operational conditions of surface suction leaching method for effective removal of partially accumulated salts from salt-damaged soil

Abstract

In dry climates, salt accumulation in soil is a large problem for agriculture. Salts accumulate partially and in a very thin surface layer of the soil at an early stage of the progress. At this stage, leaching should be conducted only in the salt accumulation zone. The Surface Suction Leaching Method (SSLM) is a desalinization method that uses minimal water. An instrument for using the SSLM consists of three components: a water supply, drainage parts, and insertion parts. The water supply has a storage tank for the leaching water and a flow pump. The drainage parts include a vacuum pump and a collection tank for the drained water. The insertion parts include a disc-shaped container with a stainless-steel guide for insertion into the soil, a ceramic or stainless-steel filter, and an inlet/outlet pipe with a bidirectional stopcock. The instrument is inserted directly into a salt accumulation zone on the soil surface. Through the stopcock, the inlet/outlet pipe is connected with the water supply and drainage parts, respectively. An operator can select the stages of water supply for either leaching or collection of water for removal of salts by switching the stopcock. The desalinization process is as follows: 1) Leaching water is poured onto the soil surface by the flowing pump; 2) The water dissolves salts accumulated in the soil surface layer. The saline remains in this layer because the amount of water supplied is too small to percolate into lower layers; 3) After switching the direction of the stopcock, the vacuum pump of the drainage parts sucks the soil saline through the insertion parts. The process is continued until the soil salinity decreases to the desired concentration. It is very important for effective desalinization using this system to determine the supply time of the leaching water and the suction time of the dissolved salts. In this study, we conducted numerical experiments to clarify the relationships among the water supply time, the suction time, the collection rate of the water, and the removal rate of the salts. We determined that the optimum technique for saving leaching water with this method is to make the water supply time short and the suction time long. However, too long of a suction time increased the amount of leaching water required. The optimum combination of water supply time and suction time under the conditions of this study was 15 seconds of supply and 600 seconds of suction.