LAUSR

Two field experiments were conducted to determine the optimum irrigation method and drip fertigation rate in menthol mint during the spring of 2015 and 2016. Experiment I comprised combinations of four drip irrigation rates [60, 80, 100, and 120% of crop evapotranspiration (ETC)] and three fertigation rates [60, 80, and 100% of the recommended dose of fertilizers (RDF), i.e. 75 kg N and 40 kg P2O5 ha−1] with an additional control (furrow irrigation and soil application of RDF). Experiment II had a split-plot design, with three irrigation methods [sprinkler, drip, and furrow irrigated raised bed (FIRB)] used in main plots and four irrigation regimes [(120, 100, 80, and 60% of cumulative pan evaporation (CPE)] for drip and sprinkler methods while maintaining irrigation water (IW): CPE of 1.2, 1.0, 0.8, and 0.6 for FIRB in subplots. Drip irrigation at 120% ETc resulted in significantly higher fresh herb and oil yield than at 100, 80, and 60% ETc. While being statistically similar with each other, fertigation with 100 and 80% RDF recorded significantly higher oil yield than that with 60% RDF. Drip irrigation at 100 or 120% ETc and fertigation with 60, 80, and 100% RDF recorded significantly higher oil yield than the control treatment. Drip irrigation led to 51.4 and 135.0% higher oil yield than FIRB and sprinkler irrigation, respectively. Drip irrigation at 120% ETc with fertigation at 80% RDF resulted in 25.4% higher oil yield, 10.1% higher biophysical water productivity, 27.1% higher economic water productivity, and saving of 34.4% IW and 20% fertilisers than the control treatment.