Shallow groundwater uptake and irrigation water redistribution within the potato root zone

Knowing the crop water uptake pattern and soil water movement within the root zone is important for the optimum design of irrigation and drainage systems. The objective of this study was to monitor the soil water redistribution within the potato root zone after irrigation and to quantify shallow groundwater contribution to water use by potatoes. The water uptake pattern in a vertical plane was monitored by TDR miniprobes installed at five different depths and at three different radial distances from the base of the potato plants. Three such planes of TDR miniprobes were used as replicates. The soil within the root zone was brought to field capacity by surface application of water. The water content measurements were carried out prior to this irrigation event and at periodic intervals thereafter over a four-day period, three times/day. The groundwater level was measured at 3 h intervals. Soil core samples were taken at each TDR probe location to determine the root density. The soil water content and upward flux from the groundwater was simulated using HYDRUS-1D model and the results were compared with the upward flux estimated from the change in groundwater levels. The maximum root density was found to be 14.5 and 252 g/m−3 at two and three months after planting. Soil layers at shallower depths showed signs of drying while the deeper layers remained wet. Model simulations closely matched the measured soil water contents and upward flux. In a fine sandy loam, up to 92% of the crop water demand was met by capillary rise from the shallow groundwater table. Knowing the shallow water table contribution can decrease the net depth of irrigation water applied and save water and energy needed for pumping.