Irrigation and fertilization improved vegetative growth and fruit development of winter jujube in plastic shed production through enhanced photosynthetic capacity and nutrient uptake

Understanding the nutritional status and photosynthetic performance of orchard crops under different irrigation and fertilization regimes is crucial for optimizing vegetative growth and promoting fruit development. To address this, the present study aimed to explore the relationships among growth indicators, photosynthetic parameters (photosynthetic rate: Pn, stomatal conductance: g s , transpiration rate: Tr, instantaneous water use efficiency: WUE i ), nutrients uptake (total nitrogen: N, total phosphorus: P, total potassium: K), and fruit development and weight based on structural equation modeling (SEM) under varied irrigation and fertilization treatments, and develop the appropriate irrigation and fertilization management strategy for sustainable winter jujube production in plastic shed. A two-year field experiment on winter jujube irrigation and fertilization management was conducted in southern Xinjiang, China, during 2023 and 2024, involving 16 drip-fertigation treatments. Treatments were as follows: four irrigation amounts (W 1 : 60% ETc, W 2 : 80% ETc, W 3 : 100% ET C , and W 4 : 120% ETc) and four fertilization rates (N-P-K, F 1 : 192-96-150 kg ha −1 , F 2 : 256-128-200 kg ha −1 , F 3 : 320-160-250 kg ha −1 , and F 4 : 384-192-300 kg ha −1 ). Results indicated that W 2 improved the N content of stems, leaves and fruits compared with W 1 . The F 3 could increase the P content and K content of fruits. The Tr was more sensitive to water and fertilizer than the Pn, resulting higher the WUE i . Irrigation and fertilization had extremely significant effects on pruning amounts ( P < 0.01), while the relative chlorophyll content (SPAD) exhibited a decreasing tendency as the irrigation amount increased. The W 2 F 2 could inhibit excessive vegetative growth while promoting fruit development. Moreover, the Logistic equation fitting for fruit volume revealed that the start time ( t 1 ) of the rapid fruit volume accumulation period range from 55.47 to 71.59 days after flowering (DAF), and the end time ( t 2 ) of the rapid fruit volume accumulation period range from 82.96 to 114.17 DAF in both years. The fresh fruit weight increased and then declined with the increase of fertilization rates. The SEM analysis revealed that the N content was the primary influencing factor for fruit volume and weight, with standardized path coefficient of 0.836 and 0.715, respectively (both P < 0.05). Additionally, growth indicators (e.g., new shoot length) exerted an indirect negative effect on fresh fruit weight. Collectively, irrigation and fertilizer can promote vegetative growth and fruit development of winter jujube by enhancing photosynthetic capacity and nutrient uptake, highlighting their critical role in winter jujube cultivation.