Drip irrigation combined with organic fertilizers improves crop N uptake and yield by reducing soil salinity and N loss in saline–alkali sunflower farmlands

Traditional border irrigation and excessive nitrogen (N) fertilization have caused severe soil salinization, NO 3 − -N leaching, and low crop yields in saline–alkali sunflower farmlands in Northwest China. To improve crop yields and N use efficiency, a three-year field experiment was conducted from 2021 to 2023 by considering drip irrigation combined with organic fertilizer application. Two irrigation levels with the soil matric potential of −20 kPa (D1) and −30 kPa (D2) were respectively designed. Three fertilization modes (WOF: without any organic fertilizer, LBF: lignite carbon-based organic fertilizer of 4.5 t ha −1 , and SMF: sheep manure of 5 t ha −1 ) were set for each drip irrigation treatment. In addition, local border irrigation combined with mineral fertilizer treatment was used as a control treatment. The soil aggregate structure, salt and N dynamics, and crop yields corresponding to these treatments were compared and analyzed. Results indicated that the LBF and SMF treatments improved the proportion of > 0.25 mm water-stable macro-aggregate and aggregate stability compared with the control treatment, thus promoting soil salt leaching. In addition, the soil desalting rate of the D1 irrigation treatment was higher than that of the D2 irrigation treatment and the control treatment. Therefore, drip irrigation combined with organic fertilizer (D1LBF and D1SMF) treatments significantly improved soil desalting with values of 21.7 %–25.3 % and 16.4 %–22.2 % higher than those of the control treatment, respectively. Furthermore, drip irrigation reduced soil NO 3 − -N leaching during growth period, whereas organic fertilization reduced its value during spring and autumn irrigation periods. Compared with the control treatment, drip irrigation combined with organic fertilization treatments significantly reduced the total NO 3 − -N leaching by 51.6 %–62.1 %. Considering the combined impact of soil salinity and N dynamics, the D1LBF treatment achieved the highest crop N uptake and yield among all treatments, which were 74.8 %–137.0 % and 43.4 %–48.8 % higher than those of the control treatment, respectively. Moreover, the water and N productivities of the D1LBF treatment were respectively increased by 47.3 %–69.8 % and 43.4 %–48.7 % compared with those of the control treatment. This then implies that drip irrigation combined with organic fertilizer application provide an efficient practice to increase crop productivity by improving the soil aggregate structure, reducing soil salinity, and reducing NO 3 − -N leaching in the saline–alkali farmlands in the arid Northwest China as well as other arid regions. • Drip irrigation and organic fertilizers promoted soil desalting by improving soil aggregates. • Drip irrigation reduced soil NO 3 − -N leaching during the sunflower growth period. • Organic fertilizers reduced NO 3 − -N leaching during spring and autumn irrigation periods. • Reduced soil salinity and NO 3 − -N leaching were the main drivers of increasing crop N uptake and yield.