The transport characteristics of water, air, and oxygen are unclear in drip irrigation systems with micro-nano bubble water, limiting its application in the field of agriculture. This study improved the method of collecting and measuring water and air flowing from an emitter on a drip irrigation system with micro-nano bubble water. The flow rate of water and air was calculated for the emitter at the beginning, middle, and end of the drip tubing. In addition, the dissolved oxygen concentration of the same emitter samples was measured. Then the transport characteristics of water, air, and dissolved oxygen along the drip tubing were analyzed. The uniformity of water, air, and dissolved oxygen for the whole pipe system was calculated. The influence of air intake rate (set by micro nano bubble machine) and system operating pressure on the transport characteristics and uniformity of water, air, and dissolved oxygen was analyzed. The results showed that the micro-nano bubbles had no significant effects on the water flow rate and uniformity (P<0.05), with the average water flow rate and uniformity remaining not less than 1.97 L/h (rated flow of 2.0 L/h) and 96.02%, respectively. The influence of air intake rate and operation pressure on the average air flow rate reached a significant level (P<0.05), as well as the interaction between other factors and operation pressure, while the influence of emitter position on the average outflow flow rate did not reach a significant level (P<0.05).Within a moderate operating pressure range (0.10-0.18 MPa), the average airflow rate and uniformity ranged from 0.13-0.23 L/h and 85.50%-92.41%, respectively, increasing and decreasing with the air intake rate increasing. At high or low operating pressures (0.22, 0.06 MPa), individual emitters in the middle of the drip pipe had abnormally high air flow rates, greatly reducing the air flow uniformity while increasing the average air flow rate of the drip irrigation system. The dissolved oxygen concentration of the drip irrigation system with the micro-nano bubble water was greatly higher than that of tap water. Its mean value increased a little bit along the drip tubing. And there was a single-peak variation trend with the increase in the air intake rate. The drip emitter position, air intake rate, operation pressure, and the interaction between the latter two had significant effects on the mean value of dissolved oxygen concentration for the whole pipe system(P<0.05). When an air intake rate of 1.5 L/min was combined with an operation pressure of 0.14 MPa, the average dissolved oxygen of the drip irrigation system reached the highest of 14.45 mg/L. Taking into account the transport effects of water flow, airflow, and dissolved oxygen, the optimal operating parameters for a drip irrigation system with micro-nano bubble water were determined to be an air intake rate of 1.5 L/min and an operation pressure of 0.14 MPa. The suitable operation pressure range was 0.10-0.18 MPa and the air intake rate range was 1.5-2.4 L/min according to the airflow uniformity>85% and the average dissolved oxygen>12 mg/L. This study provides a theoretical basis for the scientific operation of drip irrigation systems with micro-nano bubble water.

Anti-clogging test is one of the most important steps to design the emitter and type selection. However, it is still lacking on the standardized irrigation water in the testing procedures. In this study, a series of emitter clogging tests were carried out with the commercially available quartz sand and natural Yellow River sand as the clogging substances. A comparison was also made on the emitter clogging characteristics of the quartz and natural sand using standard test. Five kinds of emitters clogging performance tests were conducted with prepared the test water: three ranges of particle size (>0.075–0.090 mm, >0.063–0.075 mm, and ≤0.063 mm) and three mixing ratios (1:1:1, 4:1:1, and 1:1:4) at three concentrations (1.0, 2.0, and 3.0 g/L). The distribution of particle size and morphologies of both materials were analyzed at the same time. The results indicate: 1) Yellow River sand particles exhibited the high roundness and low clay content, while the quartz sand particles were characterized by the low roundness, sharp edges, and high clay content. These differences in particle size distribution and morphology led to more severe clogging with the quartz sand, compared with the natural sand. The deviation of clogging (Dc) was used to evaluate the difference between the average relative flow rate of Yellow River sand and quartz sand during the experiment period. And the Dc value was higher at 1.0 g/L or the predominant 0.075–0.090 mm particle fraction. However, the Dc value was the minimum at 3.0 g/L or with a predominance of particles smaller than 0.063 mm. 2) Both quartz sand and Yellow River sand exhibited the similar trends in the decrease of individual emitter flow rates, due to clogging. The drop from normal flow rate to complete clogged (flow rate reduced to 0) was usually completed within 8h. There were also the similar flow rate recovery and flow overload (exceeding the emitter rated flow rate) of clogging emitter in both particles conditions. However, the average and maximum of emitter relative flow rate (the maximum relative flow rate of 150.36%) with quartz sand were much larger, when the overload occurred, compared with Yellow River sand. 3) The clogging differentiation (Dcr) was used to evaluate the differences between the clogging behavior of the five kinds of emitters, indicating the even distribution. The clogging of quartz sand was more serious than that of Yellow River sand under the same conditions. Quartz sand demonstrated the higher Dcr at lower particle concentrations, but the lower Dcr at higher concentrations, compared with the Yellow River sand. 4) A systematic analysis was made to consider the clogging deviation of average emitter flow rate, individual emitter flow rate variation, and differentiation of clogging among five kinds of emitters. It was concluded that the quartz sand can be expected to replace the Yellow River sand as clogging substances, in order to prepare the standardized water for the emitter clogging performance tests, when using 1:1:1 mass ratio mixture of the three particle size ranges (0.075–0.090 mm, 0.063–0.075 mm, and ＜0.063 mm) at a concentration of 2 g/L. This finding can provide the scientific evidence to standardize the emitter anti-physical clogging tests. A viable approach can be offered to select the quartz sand as the substitute for the natural Yellow River sand, in order to optimize the water source for the emitter test.