Reducing evaporation from phreatic water and soil resalinization by using straw interlayer and plastic mulch

Abstract: Soil salinization severely restricts sustainable agricultural development in the Hetao Irrigation Distract in Inner Mongolia of China. Furthermore, insufficient drainage and over irrigation have aggravated the development of salinization of soil in this area. As such, people are forced to use better and more effective approaches for soil and water management in saline fields to increase crop productivity. The positive effect of both burial of straw interlayer and plastic mulch on the soil infiltration and/or evaporation has been reported, but there is a paucity of information on the effect of combined straw interlayer with plastic mulch, particularly its influence mechanism. With the aim of revealing the beneficial effects of straw interlayer and plastic mulch on water storage and salt control, a laboratory simulation experiment was conducted to study the processes of soil water infiltration and evaporation with the shallow groundwater table, as well as the distribution and transportation of soil water and salt. In the infiltration process, two treatments were designed, including homogenous soil as a control and straw interlayer buried at 40 cm depth. In the consequent process of water evaporation, plastic mulch and non-mulch practices were added respectively based on the previous treatments. The results showed that the straw interlayer buried treatments not only reduced the water infiltration rate and advanced the wetting velocity, but also induced the instability of the wetting front, i.e., the appearance of the preferential flow in the infiltration process. On the other hand, the straw interlayer buried treatments dramatically reduced the groundwater evaporation, and decreased the cumulative evaporation by 75.07%~95.42% during the successive evaporation of 30 days, when compared with the levels of control. In addition, the burial of straw interlayer altered the distribution and transportation of soil water and salt in soil profile. The soil water content in the straw interlayer imposed treatments at the top soil layers was increased while salt content was decreased in the infiltration process, compared to the corresponding ones without the straw interlayer treatments due mainly to the promoted solute leaching efficiency. Primarily, the soil capillary being cut off by the straw interlayer thereby salts up in the straw interlayer buried treatments was controlled, and blocked in the deeper soil layers during the evaporation process. Throughout the experiment, plastic mulch also had an effect of retaining soil moisture and preventing salt accumulating to the surface soil layer. However, the potential effect of mulched with plastic film only on controlling salt accumulation was not as significant as the straw interlayer buried only did. Moreover, the combination of straw interlayer and plastic mulch treatment performed better to prevent water evaporation and salts built-up in the soil than either non-mulch, or the individual use of straw interlayer or plastic mulch. Therefore, a combined straw interlayer and plastic mulch would provide a better edaphic environment for crop growth in agricultural production. The results of this study provide a reference for salt control and water conversation, as well as field management practices in an arid area and saline field.