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Overapplication of nitrogen fertilizer and water in vegetable production is popular and serious in China and other developing countries, leading to severe environmental pollution. To date, most model-based decision support systems, which are believed to be powerful tools for improving fertilizer and water management in vegetable production, have been established by developed countries, and the weather, soil, hydrology, facility type and vegetable species of developing countries have been less considered. In this study, a water level component and a new vegetable species, pakchoi (Brassica campestris ssp. Chinese) were incorporated into EU-Rotate_N, a simulation model developed by the European Union for open field vegetable cultivation. The experiment was carried out in typical vegetable plastic tunnels in Jiangsu Province, China, an area with high groundwater level. The results indicated that the water level algorithm which differentiate the soil into saturated and unsaturated layers enhanced the model simulation accuracy of the soil nitrogen and water content in the 30 cm soil layer, indicating the significant influence of groundwater on the soil water and nutrient movement. The pakchoi experiment suggest that new vegetables could be added into the crop list of EU-Rotate_N by adjusting parameters with 'trial and error' methods after considering its biological characteristics. Furthermore, a novel module was added for recommendations of fertilization and irrigation on daily basis in accordance with reasonable upper and lower thresholds of soil water content and soil available nitrogen after a series of adjustment. Finally, a user-friendly application (APP) was developed based on the improved model. The evaluation experiments in 2021 and 2022 showed that APP could significantly improve nitrogen and water use efficiency without obvious yield loss in pakchoi production. We conclude that simulation models for vegetable fertilizer and water management established by developed countries could be modified by several operable steps to expand its application area. • An algorithm was added in EU-Rotate_N and its performance in high groundwater level was improved. • New vegetable pakchoi was successfully added, indicating crop scopes of the model can be expanded. • A user-friendly APP that support multiple users was developed with daily fertilization and irrigation recommendations. [ABSTRACT FROM AUTHOR]

Highlights • Shallow groundwater had a considerable contribution on cucumber evapotranspiration. • In this condition 75% of estimated cucumber ETc optimize cucumber yield. • Using fertigation, 75% of the traditionally recommended N optimize cucumber yield. • Frequent irrigation with low water volume is important when water table is high. Abstract The middle and lower reaches of Yangtze River present high rainfall and always have a high water table. Recently drip fertigation has been introduced and widely used for vegetable production in this area. To investigate the effect of shallow groundwater and the newly-developed fertigation on the cucumber water and nitrogen (N) requirement, experiments were carried out in plastic tunnels in Yangzhou, Jiangsu, China, during the 2016 and 2017 growing seasons using a randomized block design with three replicates. Four N rates, 4 irrigation amounts and 2 irrigation intervals (2 d and 4 d) were applied in this experiment. The results showed that irrigation amount of 75% of estimated plant evapotranspiration (ET c) was optimal to obtain the highest yield, indicating shallow groundwater had a considerable contribution to the cucumber plant evapotranspiration in this condition. Fertigation technology improved the irrigation water use efficiency (IWUE) and N use efficiency (NUE) and 75% of the recommended N rate (calculated according to a traditional local nutrient balance method) optimized cucumber yield. Frequent irrigation with low water volume had a beneficial impact on the improvement of cucumber yield, IWUE, NUE and reduced the N leaching. According to this work, the recommended fertigation strategy is 0.75 of recommended N, 0.75 estimated ET c and 2 d irrigation interval in this experiment, in which cucumber yield of 105.4 Mg ha−1, IWUE of 41.1 kg m-3 and NUE of 356.4 kg kg−1 were achieved. [ABSTRACT FROM AUTHOR]