Water and potassium (K) management is an important measure to improve fruit production in citrus orchards, but its effects on rhizosphere microenvironment and soil water-nutrient utilization are still unknown. In this study, two degrees of water deficit (20% and 40%) and three degrees of K fertilizer deficit (20%, 40% and 60%) were set at citrus fruit expansion (stage III) and maturation stages (stage IV), respectively. Results showed the III-HWHK treatment increased soil ammonium availability. This effect was attributed to a higher abundance of nitrogen (N) fixation genes ( nifD and nifK ). Additionally, the treatment suppressed denitrification genes ( nirK and norB ) and denitrifiers ( Ochrobactrum , Rhizobium , and Achromobacter ). The IV-HWMK treatment improved soil nitrate availability by increasing the relative abundance of the amoC gene and ammonia-oxidizing archaeal Nitrosocosmicus . Redundancy analysis (RDA) showed that soil pH, NO 3 - -N and available K (AK) were the main factors affecting rhizosphere nitrifiers and denitrifiers. Moreover, III-HWHK and IV-HWMK treatments significantly increased citrus fruit yield, partial factor productivity of nitrogen (PFP N ), partial factor productivity of potassium (PFP K ), and irrigation water productivity (WP I ) by 7.10%-68.83%, 7.10%-68.83%, 8.95%-51.00% and 8.88%-73.42%, respectively, in 2023 and 2024. The structural equation model (SEM) indicated that optimizing irrigation and K fertilizer could increase citrus yield characteristics by improving soil inorganic N availability. Therefore, III-HWHK and IV-HWMK treatments at fruit key growth stages were the best water-potassium management modes to promote citrus production. These findings provide important guidance for increasing soil water-nutrient utilization and improving the rhizosphere microenvironment in citrus orchards in Southwest China.
Zha et al. (2026) studied this question.