The combined effect of water and potassium on physiological traits of jujube leaves and fruit yield under drip irrigation in Southern Xinjiang

[Objective] Jujube is a vital cash crop in Xinjiang. This study examined the combined effect of irrigation and potassium fertilization on physiological traits of jujube leaves and fruit yield to determine the optimal irrigation and fertilisation strategy for its sustainable production in this region. [Method] The field experiment was conducted from 2022 to 2023 in an 8-year grey jujube orchard in Aksu, Southern Xinjiang. There were three irrigation treatments by irrigating 100% (T1), 75% (T2) and 50% (T3) of estimated evapotranspiration. Each irrigation treatment had three potassium fertilizations: 240 kg/hm2 (A), 180 kg/hm2 (B) and 120 kg/hm2 (C). During the experiment, we measured the photosynthetic traits of the jujube leaves and ultimate fruit yield. [Result] Both irrigation amount and potassium fertilization significantly impacted growth and development of the jujube. The net photosynthetic rate, transpiration rate and chlorophyll content of the jujube increased with increasing irrigation amount and potassium fertilization. Increasing potassium fertilization increased soluble sugar in jujube leaves, with its content in T1-A, T2-A and T3-A in 2023 increasing by 37.0%, 36.9% and 28.7%, respectively, compared to that in 2022. The abscisic acid (ABA) in jujube leaves varied with irrigation amount, being the highest in T3-C. The irrigation water use efficiency increased as the plant grew, and the fruit yield increased with the increase in potassium fertilization. When potassium application was 240 kg/hm2, T1 and T2 increased the fruit yield by 56.77% and 45.52% in 2022, and 51.46% and 37.61% in 2023, compared to T3. Water use efficiency of T2-A was 8.88 kg/(hm2·mm) and 9.14 kg/(hm2·mm) in 2022 and 2023, respectively. [Conclusion] Among all treatments we compared, irrigating 75% of estimated evapotranspiration combined with a 240 kg/hm2 of potassium fertilization is optimal for improving fruit yield and water use efficiency of jujube in Southern Xinjiang.