The present invention provides subsurface irrigation systems and air injection mechanism and microbubble generating mechanism. The systems of the present invention are operable to provide an evenly distributed air microbubbles in a stream of fluid (e.g., subsurface irrigation water) to evenly provide gas therein (e.g., oxygen for plants receiving the irrigation water along an entire length of an irrigation line). The microbubble generating mechanism may use pressure generated from flow of fluid to cavitate the fluid and thereby distribute gas microbubbles in the fluid. In irrigation examples, the resulting air infused water delivers an effective amount of oxygen to the roots of the irrigation crops.
