Dynamic changes in bubble profile due to surfactant and tape orientation of emitters in drip tape during aerated water irrigation S.P. Bhattarai a,⇑ , R.J. Balsys b , P. Eichler c , D.J. Midmore a , D. Wassink d a Central Queensland University, School of Medical and Applied Sciences, Rockhampton, Qld 4702, Australia b Central Queensland University, School of Engineering and Technology, Rockhampton, Qld 4702, Australia c Rio Grande do Sul State University, Novo Hamburgo, RS 93340-140, Brazil d Australian Nuclear Science and Technology Organisation, Menai, NSW 2234, Australia article info Article history: Received 23 June 2014 Received in revised form 21 March 2015 Accepted 11 May 2015 Available online 21 May 2015 Keywords: Aeration Oxygation Air injection Irrigation water Bubble visualisation abstract Use of aerated water for drip irrigation using a pressure differential Venturi has been reported to produce positive response on crop yield and water use efficiency. We present two options for increasing the distance from the source of irrigation an air/water mixed phase travels. We discuss observed results for a row length of 500 m of drip tape. The first option relates to the orientation of drip tape emitters to the ground plane. In the up orientation the emitters are on the top of the drip tape and in the down position the emitters are along the bottom of the drip tape. We found higher air void fraction with the emitters down, compared to the standard placement with the emitters up. We also discuss observations of field trials for this treatment. The second option explored two concentrations (2 ppm and 4 ppm) of BS1000™ surfactant in irrigation water in the drip tape. Bubble size decreased, whereas air void fraction increased along the length of drip tape, with increased concentration of surfactant, in both up and down emitter positions in the drip irrigation tape. The best result was using non-ionic surfactant at 4 ppm with the emitter facing down where the bubble distribution and the availability of micro-bubbles over the 500 m irrigation was greatest. This knowledge will be of benefit in drip and sub-surface drip irrigated agriculture. Crown Copyright Ó 2015 Published by Elsevier Ltd. All rights reserved. Introduction Our aim is to be able to quantify the air void fraction and dis- solved oxygen (DO) concentration along the length of tape in drip irrigation (DI) and subsurface drip irrigation (SDI). We will use this information to obtain better agricultural and environmental out- comes by studying the effects of the DO and air in the form of bub- bles on plant and soil chemistry. We believe that DO and air bubbles in water play different roles in the root zone, their relative effects are unknown and of research interest. Being able to get water with significantly greater air void fraction and dissolved oxy- gen (DO) concentration further down the DI or SDI tape is an important outcome. We do this to increase the oxygen supply to the plant root zone. Poor oxygen supply in the root zone of crop plants can be a major bottleneck in irrigated farming. Evidence of hypoxia associated with drip and subsurface drip irrigation has been well documented (Silberbush et al., 1979; Goorahoo et al., 2002; Bhattarai et al., 2005). The purging of soil air and thus oxygen out of the root zone in response to irrigation has been ter- med the irrigation paradox. Water used for irrigation purposes can often experience a low DO value, particularly at higher tempera- ture, saline irrigation water, and water with high critical oxygen demand (COD). Soil aeration has been recognised as a major limitation of irri- gated crop production for more than 60 years (Wiersma and Mortland, 1953). Early air injection methods used a compressor to deliver compressed air to the root zone via drip tape. In this method the distribution uniformity of air is rather poor, as the compressed air tends to escape from the drip emitters by the chim- ney effect (Goorahoo et al., 2002), i.e. as large volume of air exiting vertically from the DI and SDI emitters along the drip tape. By adapting Venturi air injectors Goorahoo et al. (2002) clearly demonstrated the benefits of using aerated water irrigation and proposed practical methods that are based on bubbles generated by the air injection system. Aerating the crop root zone using hydrogen peroxide (H 2 O 2 ) or injecting air using a Venturi principle in DI and SDI in hostile soil such as vertisols is discussed in Bhattarai et al. (2004, 2006). Hydrogen peroxide application, in spite of its positive benefits http://dx.doi.org/10.1016/j.ijmultiphaseflow.2015.05.008 0301-9322/Crown Copyright Ó 2015 Published by Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: s.bhattarai@cqu.edu.au (S.P. Bhattarai). International Journal of Multiphase Flow 75 (2015) 137–143 Contents lists available at ScienceDirect International Journal of Multiphase Flow journal homepage: www.elsevier.com/locate/ijmulflow