Coupled soil moisture management and alginate oligosaccharide strategies enhance citrus orchard production, water and potassium use efficiency by improving the rhizosphere soil environment

Optimizing soil water and fertilizer management can benefit crop production and soil environment. Alginate oligosaccharides (AOS) are natural biostimulants with fertilizer efficiency- and growth-promoting functions. However, there are few application strategies of AOS in citrus production, especially in combination with water and fertilizer regulations. In this paper, a two-year field trial was conducted to investigate the effects of AOS (AOS0, AOS2.5, AOS5.0) strategies under different moisture conditions (W80, W70, W60) on citrus yield, quality, water and fertilizer use efficiency, plant growth and soil environment. The results showed that drip irrigation with 2.5 g L−1AOS 8–10 times under W70 (W70AOS2.5) increased fruit yield, the total soluble sugar and sucrose content by 11.93%–13.31%, 15.16–17.47% and 18.92–20.81%, and fruit potassium and water use efficiency increased by 51.09%–62.21% and 12.01%–13.34%, respectively, and the effect of increase was better than the application in W80 and W60. Citrus growth showed that net photosynthetic rate of W70AOS2.5 were significantly increased after 4th AOS application, and that total root length, surface area, and volume also increased at harvest. Soil analysis showed that drip-irrigated AOS reduced the loss rate of soil water under both W60 and W70, increased proportions of water stable aggregates >0.25 mm in the soil. The available potassium content increased significantly in the 0–20 cm soil layer but decreased significantly in the 20–40 cm soil layer, and soil cation exchange capacity also increased significantly in the 0–20 cm layer, suggesting that AOS may slow water and potassium loss under low moisture conditions. In addition, AOS also increased the organic carbon content and the abundance of Pseudolabrys which dominant bacteria associated with carbon and nitrogen. The W70AOS2.5 strategy exceeded other strategies in terms of overall evaluation score and net benefits, reducing irrigation water discharge to the environment by 620–700 m3 ha−1. Our study demonstrated the good potential of AOS in improving fruit production and soil properties.