Dynamics of Moistube discharge, soil-water redistribution and wetting morphology in response to regulated working pressure heads

Moistubes continuously irrigate crop-root zone through tube nanopores, as required based on crop water demand. This study investigated the soil water dynamics under adjusted working pressure heads (WPHs) in Moistube and revealed whether wetting patterns and moisture distribution can be artificially regulated. Six scenarios of adjustments were designed, WPH increase from 0 to 1, 0–2, and 1–2 m, and WPH decrease from 1 to 0, 2–0, and 2–1 m. Wetting patterns were analyzed using image processing. Moistube discharge and moisture distribution within wetting patterns were analyzed. Results demonstrated that following WPH adjustment, the Moistube discharge rate, moisture distribution and wetting morphology significantly changed. The cumulative infiltration and infiltration rate rapidly changed without buffering process at the adjustment points. The infiltration rate at certain WPHs showed a slightly decreasing trend obeying an exponential-type model. When the WPH was adjusted, the infiltration rate rapidly increased or decreased to values that linearly correlated with WPH, respectively. The wetting front deviated from the original advance trend and accelerated or decelerated, with increased or decreased WPH, respectively. We proposed a physical-empirical model based on Green-Ampt model theory under a polar coordinate system. This model exhibited satisfactory performances on Moistube discharge and wetting front advance under adjusted WPHs. Wetting pattern center rapidly deviated from the Moistube center following greater WPHs, with the deviation positively correlated with WPH. Soil remained unsaturated around Moistubes. The soil water content (SWC) within the wetting patterns was governed by WPH adjustments. SWC gradually increased or decreased with WPH increase or decrease. Our results suggest that increasing WPH remarkably affected soil-water dynamics, while the effects of WPH decrease on wetting pattern advance were not noticeable, which exhibited a slight expanding of wetting patterns with uniformly redistributed and decreasing SWC. The feasibility of regulating Moistube discharge, wetting morphology and SWC favors synchronously satisfying crop water requirements.