Oxygation refers to irrigation of crops with aerated water, through air injection using the venturi principle or the supply of hydrogen peroxide in the root zone, both using subsurface drip irrigation (SDI) system. Oxygation improves water use efficiency (WUE), producing more yield and, and therefore, optimizes the use of drip and SDI. But the efficiency of oxygation is quite possibly dependent on a number of factors. The primary objective of this study was, therefore, to quantify the effects of oxygation, emitter depths and soil type on crop root zone oxygen content, soil respiration, plant physiological response, biomass yield, quality and WUE of three crop species. This study investigated the potential of oxygation to enhance soil respiration, plant growth, yield and water use efficiencies (WUE) of cotton and wheat in experiments in enclosed heavy-duty concrete troughs (tubs) and pineapple and cotton in field experiments. Experimental treatments in tubs for wheat included comparisons between two soil types (vertisol and ferrosol) and superimposed were two oxygation methods (Mazzei air injector and Seair Diffusion System) compared to a control, and for cotton, emitters at two depths using Mazzei air injectors were compared to a control. The field experiments compared Mazzei air injectors and a control for cotton in Emerald and pineapple in Yeppoon, both in central Queensland, Australia. In all experiments, soil oxygen content and soil respiration markedly increased in response to the oxygation treatments. The O₂ concentration in the crop root zone increased by 2.4–32.6%, for oxygation compared to control at the same depth. The soil respiration increased by 42–100%. The number of wheat ears, leaf dry weight and total dry matter were significantly greater in Mazzei and Seair oxygation compared to the control. Fresh biomass of wheat increased by 11 and 8%, and dry weight of wheat increased by 8 and 3% in Mazzei and Seair oxygation treatments compared to the control, respectively. Likewise, the irrigation water use efficiency increased with oxygation compared to the control in wheat. The yield, WUE and number of other physiological parameters in wheat were enhanced in vertisol compared to ferrosol. The seed cotton yield in the tub experiment increased with oxygation by 14%, and significant differences for fresh biomass, dry matter and yield were also noted between oxygation and the control in the field. Lint yield and WUE both increased by 7% using Mazzei in the cotton field trial during 2008–09. There were significant effects of oxygation on pineapple fresh biomass, and dry matter weight, industry yield and a number of quality parameters were significantly improved. The total fruit yield and marketable increased by 17 and 4% and marketable WUE increased by 3% using Mazzei. Our data suggest that the benefits of oxygation are notable not only for dicotyledonous cotton but also for monocotyledonous wheat and pineapple representing different rooting morphologies and CO₂ fixation pathways.

Population density of industrial hemp (Cannabis sativa L.) in the field influences crop growth habit, fibre yield and quality. Therefore, optimization of plant population density is required to control growth and