Abstract:
Moistube continuously fertigates the crop-root zone through the nano pores on the Moistube, as required by the crop water demands. To investigate the Moistube discharge and water movement, a series of Moistube irrigation experiments was conducted under different regulated working pressure heads(WPH) in Moistube. The scenarios of WPH increase(0→1 m, 0→2 m and 1→2 m) and WPH decrease(1→0 m, 2→0 m and 2→1 m) adjustments were designed. The Moistube discharge, wetting front advance and soil water dynamics were studied. The HYDRUS 2D model was used to simulate the Moistube discharge and soil moisture transport under regulated WPH, by assuming the Moistube as a porous medium clay. After the model performance was validated, the soil moisture dynamics of moitube irrigation under scenarios of multiple WPH adjustments were analyzed accordingly. The results showed that regulation of WPH significantly changed the cumulative infiltration volume and infiltration rate with respect to time. The curve of cumulative infiltration with time was manifested as a fold line comprising of two interaction lines. The slope of lines was increased or decreased regularly with WPH adjustment. WPH adjustments gave rise to sudden increases or decreases in infiltration rate, and the stabilized infiltration rate was linearly correlated with the adjusted WPH. With increase of WPH, the moisture content within the wetting front was sharply risen, displaying significantly positive feedback. When the WPH was decreased, the water content around the Moistube was slightly decreased, and then rose gradually as the moisture redistributed. The Moistube was treated as a clay porous medium, and the Moistube discharge and water flow transport was well simulated based on the HYDRUS 2D model. The model performances were rated as ‘good’, with coefficient of determination(R~2) greater than 0.90, the Nash-Sutcliffe efficiency(NSE) was not less than 0.70 and RSR approached 0. Multiple WPH regulation scenarios(0→1→2 m, 0→2→1 m, 1→0→2 m, 1→2→0 m, 2→0→1 m and 2→1→0 m) were formulated. The soil-water dynamics around the Moistube under all scenarios were analyzed. It was found that the infiltration rate showed exponentially decreasing and subsequent stabilizing trend with respect to time after the WPH was increased. However, following a decrease in WPH, the infiltration rate showed an exponential increase followed by stabilization. The final cumulative infiltration volume was maximum under the consecutive incremental WPH scenario(for instance, 0→1→2 m); and the consecutive decremental WPH scenario(2→1→0 m) resulted in a minimum cumulative infiltration, which was reduced by 3.7% compared with the 0→1→2 m treatment. It was feasible to regulate the wetting front advance and the moisture condition within the wetting front by adjusting WPH. The moisture condition around the Moistube was more sensitive in response to the regulation of WPH. The results provided scientific and theoretical basis for dynamically regulating the working pressure head of Moistube. The Moistube irrigation technique could also be integrated with intelligent irrigation by automatically adjusting the WPH, in order to maintain an appropriate water environment within the root zone and to conduct precise irrigation.