Groundwater Evaporation for Salt-Affected Soil Under Plastic Film-Covered Cultivation Condition: a Review

Abstract

Groundwater is a main type of natural resource, and groundwater evaporation is an important part of the cropland water cycle. Under recent years of poor land management, soil salinization is becoming a serious environmental issue, especially in the arid regions having strong evaporation and shallow groundwater table. Plastic mulching has therefore emerged gradually, becoming a globally applied agricultural practice for its benefits such as salt cumulation control, soil environment regulation, and crop yield improvement. However, knowledge of groundwater evaporation under plastic film-covered cultivation pattern remains vague in terms of action mechanism. This review critically discusses how plastic mulch, salt, and crop cultivation/plant by-products affect groundwater evaporation and further reveals their action mechanisms. For salt-affected cultivated soils, specifically, salt precipitation, crystallization, and capillary force are the non-negligible actions affecting water movement and evaporation. Besides, the physical and chemical effects of formed salt crust at plastic film holes cannot be ignored under plastic mulch underlying condition. Furthermore, the effect of changed canopy cover during growing period should be taken into consideration under crop cultivation underlying condition; meanwhile, the variation of water flow and evaporation induced by crop residues or direct straw return in farmland can be quantified through determining the amount of the hydrophilic oxygen-containing functional groups and the change of soil pore-size distribution. Based on the current research deficiency, future studies should focus on the groundwater contribution to crop, the diurnal variation of groundwater evaporation, the determination of suitable and ecological groundwater table, and the capillary rise models; and future interdisciplinary (e.g., physics and chemistry) research should be put into the interactive of salt and water in order to reveal the mechanisms of fresh and saliferous groundwater flow and evaporation; moreover, the issue on plastic pollution induced by plastic mulch should also be brought to the forefront. A clear understanding of groundwater evaporation under plastic film-covered cultivation on salt-affected soil benefits environmental protection in the saline regions.