This study highlights the integration of high-frequency water quality monitoring in evaluating the effectiveness of microalgae-based soil probiotics applied to young macadamia trees. A mobile monitoring station collected nutrient data several times daily, capturing short-term dynamics such as rainfall-induced fertiliser runoff. The data supported the development of a decision support tool for optimised fertilisation. Results indicated that probiotics can improve soil water retention by an average of 11% (up to 35% in dry years) and reduce nitrate fertiliser use by an average of 25%, or 45 kg/ha annually.