Assessing the influence of integrating soil amendment applications with saline water irrigation on Ajwain’s yield and water productivity

Freshwater scarcity and soil salinity are amongst the main obstacles for sustainable development of irrigated agriculture, particularly in arid regions. A 2-year field investigation was conducted at an experimental field in south-east Iran during the 2017 and 2018 growing seasons to evaluate the individual and integrated effects of water-saving irrigation strategies and organic soil amendment (OSA) applications on yield and water productivity of ajwain (Trachyspermum ammi), which is known as an important medicinal plant in Iran. A split-plot design with 16 treatments was used in the field trial. Treatments were created by combining four irrigation strategies, including full irrigation with freshwater [FF], partial root-zone drying (PRD) with freshwater (PF), PRD with saline water (PS), and PRD with alternating application of fresh and saline water (PFS), were combined with four types of soil amendments, including no amendment (control), charcoal nano-biochar (NB), composted cow manure (CM), cow manure vermicompost (VM). Results showed that in the absence of OSA application, exposing crops to salinity/water stresses caused 3.7–17.6% and 4.5–17.7% reduction in the crop’s seed yield and above-ground biomass, respectively, while enhancing the crop’s oil concentration and oil yield by 9.1–30% and 1.4–18.3%, respectively. Along with a 34–63% freshwater saving, a 24.9–91.2% increase occurred in the crop’s water productivities compared to the FF treatments. Integrating OSA application with freshwater-saving irrigation caused up to 58, 27.1, 60, 138, and 285% increase in the crop’s seed yield, biomass, oil concentration, oil yield, and water productivity, respectively, compared to the FF-control treatment. However, VM performed best, and CM took second place. Based on the results, it can be concluded that such integrations provide opportunities for developing Ajwain’s production in arid regions with limited access to freshwater resources.