Study on irrigation scheme and nitrogen application to sunflower (Helianthus annuus L.) in saline farmland in the arid/semi-arid region of Hetao Irrigation District

Water scarcity, salinity stress and excessive use of nitrogen fertilizers are the main threats to agricultural production in arid/semi-arid Hetao Irrigation District (HID), China. This study investigated the effects of different water and nitrogen management strategies in various hydrological years. An agricultural hydrological model was employed to simulate changes in soil moisture, salinity, nitrogen application rates, crop growth, and yield. The results showed that an irrigation strategy aiming to water stress (MAD ≤ p) enabled the crop to bypass salinity stress and achieve higher yields. (For example, the wet year of 2020 required 78.8 and 75.3 mm of irrigation on July 29th and August 21th, respectively. The dry year of 2021 required 74.9, 75.7 and 76.8 mm of irrigation on July 20th, July 31th and August 15th, respectively.) The effect of MAD > p irrigation strategy on sunflower yield and nitrogen leaching was relatively small, and the use of MAD ≤ p irrigation strategy increased sunflower yield but also increased nitrogen leaching. The results of the combined piecewise structural equation modelling indicated that when soil water content was low and soil salinity was high, nitrogen fertilizer could be applied appropriately to reduce salt stress on the crop. Considering sunflower yield, water use efficiency, water infiltration, and nitrate N leaching together, a higher yield and less NO-N leaching could be obtained by irrigating 150 mm and applying 140 kg ha of N in wet years and 240 mm and 180 kg ha of N in dry years. The results were used to comprehensively evaluate the effectiveness of irrigation and nitrogen application in the HID, and to optimize irrigation and nitrogen management strategies, with the aim of reducing water consumption, enhancing irrigation efficiency, and mitigating the risk of nitrogen leaching.