The soil water dynamics and hydraulic processes of crops with plastic film mulching in terraced dryland fields on the Loess Plateau

The soil water supply is the main limiting factor for dryland crop production on the Loess Plateau in China. Local farmers have been looking for tactics to interfere with natural hydrologic processes and to conserve soil water in dry seasons. Recently, plastic film mulching has been widely used by local farms. Moreover, mulching no longer occurs before planting, instead, it is done earlier, and thus crop yields increase. Therefore, soil water hydrologic processes for fields mulched entirely with plastic film mulch require better understanding. Field experiments were conducted from October 2009 to September 2010, 2011, and 2013 to evaluate the soil water dynamics and hydrologic process in winter wheat, maize, and potato fields with plastic film mulching. The soil moisture for depths of 0–100 cm in 2010–2011 and 0–200 cm in 2013 was measured at every 20-cm depth interval during the growth period from sowing to harvesting in all of the treatments. The results showed that the soil water distribution of a plastic film-mulched field is significantly different from that of an unmulched field. The soil water of the mulched field presented an obvious inverted S-trend at depths of 0–60 cm during the growth season. During the dry season (winter and spring), under conditions of high surface evaporation and no effective rainfall, changes in the boundary conditions of the vapor migration hydrologic process between the soil and atmosphere by the mulched treatments led to an obvious increase in the soil water with wheat increasing by 3.45 (cm³/cm³) at depths of 0–20 cm and maize and potato increasing by 0.04–6.04 (cm³/cm³) at depths of 0–80 cm. This condition increased the available water to guarantee the crops’ water demand at the dry seedling stage for maize and the revival stage for wheat against the threat of seasonal drought and ensured a higher crop yield.