Impacts of gas source and surfactant on gas-water coupling transmission along a long-distance drip tape in one or two line layout under aerated drip irrigation

Abstract: Aerated drip irrigation (ADI) is a technique to aerate the rhizosphere by aerated water through the drip irrigation system. The dissolved oxygen (DO) in water, water flow rate and gas flow uniformity are the essential indexes for the evaluation of irrigation quality in ADI. The use of biodegradable surfactant BS1000 and the optimization of transmission modes are of great significance in the existence of microbubble and the retention of DO in water during ADI. To increase the uniformity of gas, oxygen and water and the delivery distance under ADI, transmission characteristics, i.e., gas-oxygen-water mixture produced by aerated irrigation system using Mazzei 1078 venturi air injector, were studied. The impacts of gas source and surfactant on gas-water coupling transmission along a long-distance drip tape in one or two line layout were investigated. Totally 16 combinations were tested, including 2 types of gas (air and oxygen), 2 transmission modes (one and two line transmission), and 4 levels of BS1000 concentrations (0, 1, 2 and 4 mg/L), respectively. During the experiment, parameters and uniformities of water flow rate, DO, gas void fraction (GVF), and water flow rate were observed. The DO and GVF of irrigation water along a drip tape were monitored by a dissolved oxygen meter and a vacuum device of gas void fraction measurement. Main results were given as below. Aeration treatment resulted in the slight reduce in the uniformity of water flow rate during one line transmission under ADI along a drip tape, but the DO concentration and GVF in irrigation water were significantly increased at the level of 0.05. The DO concentration in air and oxygen aerated water were increased by 160.80% and 617.05% compared with non-aerated treatment during one line transmission. However, DO levels in air and oxygen aerated water were increased by 185.26% and 643.23% compared with non-aerated treatments during two line transmission. Use of biodegradable surfactant BS1000 concentration brought an increase in GVF. Under the condition of air aerated treatment during one line transmission, the GVF at 1, 2 and 4 mg/L of BS1000 were significantly increased by 17.42%, 60.41% and 80.32% than the non-use of surfactant treatment, respectively. Similarly, under the condition of oxygen aerated treatment during one line treatment, GVF at 1, 2 and 4 mg/L of BS1000 were significantly increased by 25.00%, 55.05% and 69.27% in contrast to non-use of surfactant treatment. The use of BS1000 had a positive effect on the DO under ADI. With the increasing of BS1000 concentration, there was no significant difference neither in uniformity of DO nor water flow rate. However, compared to non-use of BS1000, the uniformity of gas flow at 4 mg/L of BS1000 was significantly decreased during one line transmission. The uniformity of water flow rate, DO and gas flow during two line transmission under ADI were higher than 95%, 96% and 67%. Compared to one line transmission, the uniformity of water flow rate, DO and gas flow during two line transmission were increased by 14.00%, 4.05% and 30.64%, respectively. Two line transmission was an optimal connection mode under ADI at the long distance of water delivery under ADI. This research will provide valuable information for optimization of aerated technique parameters and drip tape layout under ADI.