Plastic Content and Size Together Produce the Dual Effects on Water Loss and Surface Fissure for Silt Loam

Evaporation is a common process in farmland under natural conditions, whereas, surface cracking associated with evaporation is always overlooked. Plastic contamination is becoming a hot issue of global concern; therefore, a clear understand of how plastics affect water evaporation and soil cracking is necessary. However, the previous research in this area was not completed. Silt loam was mixed with two concentrations (0.1 and 0.5%, w/w) of plastic residual films each with three sizes (10, 5, and 2 mm) and undergone the natural evaporation experiments, during which the water loss and surface fissure parameters were obtained. Results showed that the presence of plastics had dual influences (i.e., promoting and inhibiting effects) on water evaporation and desiccation cracking, which were determined by the content and the size of plastics. In the case of 0.1% plastic added, the plastics less than 10 mm in size promoted evaporation, which increased with the increasing plastic size by creating channels for water movement. In the case of 0.5% plastic added, the large plastic with 10 mm inhibited evaporation instead due to the formed waterproof layer in the soil. Water evaporation and desiccation cracking changed synchronously and affected each other. The crack area has an extreme significant effect on water evaporation and soil water, but crack length did not. The variation of total crack area for both 0.1 and 0.5% plastic added treatments was the same as that of water evaporation. Further studies should focus on other soil types to confirm the dual influences found.