Water scarcity has negative effects on plants. This study investigated the interactive effects of irrigation intervals and humic acid (HA) application on the growth, physiological, and biochemical traits of Dichondra repens, an important ground cover in green space. The experiment was carried out using a factorial completely randomized design with irrigation intervals (7, 9, 12, and 14 days) and HA levels (0, 250, 500, and 1000 ppm). The results showed that there is a significant interaction between irrigation intervals and HA on most traits. The highest shoot and root weight, stolon number, and root length were recorded at the 7-day irrigation interval with 1000 ppm HA. Increasing drought stress reduced growth traits but increased chlorophyll and proline contents as adaptive responses. The observed increase in proline content in dichondra under specific irrigation intervals and humic acid treatments highlights the complex interplay between water availability and soil amendments. It was observed that HA decreased the drought effects by increasing the antioxidant activity, relative water content and decreasing electrolyte leakage. Enhanced defensive responses in the plant against drought stress were further confirmed by increased antioxidant activity and higher proline content. The phenol content also increased with HA application, while the flavonoid content remained unaffected. In conclusion, HA significantly improves drought tolerance in D. repens by promoting morphological, physiological and biochemical resilience under extended irrigation intervals. These findings support the use of HA as a sustainable biostimulant in green spaces to maintain plant quality in drought conditions.

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