Optimization of water use and determination Water-Salinity-Yield Production Function of Mentha piperita L in the presence of Selenium

Water scarcity particularly in arid and semi-arid areas has been threatening food security for millions of people. Considering that Iran is located in an arid and semi-arid zone and crop production is not possible without irrigation management. In areas where crops are irrigated management and proper planning are necessary for optimal use of water. Due to the quantitative and qualitative decline of groundwater resources, it is essential to optimize water use in agriculture. One of the methods to optimize water use in agriculture, especially in arid regions, is to use yield-water-salinity functions. Also, Selenium has been introduced as one of the useful elements against the destructive effects of salinity and water stresses. Peppermint with the scientific name Mentha piperita L is one of the medicinal and aromatic plants whose essential oil has many medicinal, food, cosmetic and health uses. Given that salinity stress and drought stresses are serious issues and problems in arid regions, in such conditions, it is very important to predict crop performance under drought and salinity conditions.Therefore, this study was performed for the prediction of Mentha piperita L yield and the determination of optimal production function under salinity and water stress conditions in a research greenhouse in the Torbat-e Jam region.One of the other innovations of this research is the investigation of the effect of selenium on these production functions and also on water productivity, with the assumption of increasing plant tolerance against salinity and drought stress.An experiment of the split in time was performed in a completely randomized block design with three replications including two levels of cut (cut1 and cut2), Salinity factor in 3 levels (0, 50, and 100 mmol NaCl, three levels of irrigation (including full irrigation (100% of water requirement) = I1, I2=75% I1 and I3= 50% I1), and selenium factor in 2 levels (0 and 5 mg/lit Na2SeO4).To properly establish the plants, the plants were irrigated every other day for two weeks after the transfer of the rhizomes, then as soon as the emergence of new leaves, the pots were treated with sodium selenate (Na2SeO4) in the form of foliar spraying with concentrations of 0 and 5 mg/l, foliar spraying was done three times every other day, and 24 hours after the last foliar spraying, plants under other treatments (salinity and drought stress) were placed. Salinity treatments were added to the pots from the lowest amount and higher concentrations were added gradually over several days. To determine water requirement was used Class A evaporation pan and water treatments were applied based on it. To calculate the water requirement, plant coefficients of peppermint were determined for the initial, development, and middle growth stages, respectively, 0.69, 1.03, and 1.27. 30 days after the application of salinity stress and drought stress, the first cut was done, for a more detailed investigation, the second cut was done 45 days after the first cut.Yield data of Mentha piperita L (yield of two cuts gathered for better estimation together), once in the presence of selenium and once in the absence of selenium were fitted to different production functions including simple linear, Cobb-Douglas, quadratic, and transient models and the optimum one was determined after sensitivity analysis. The results showed that the coefficient of determination (R2) for estimation of the yield in the presence of selenium by quadratic, transcendental, simple linear, and Cobb-Douglas functions were 0.986, 0.981, 0.946, and 0.897, respectively. In the absence of selenium these coefficient were 0.998, 0.995, 0,959 and 0/871, respectively. According to the results of this research, the quadratic production function is recommended as the optimal production function for the yield of Mentha piperita L in the presence and absence of selenium in the Torbat-e Jam region. Therefore, to optimize the agricultural water consumption for the peppermint plant, it is suggested to use the quadratic production function in this region. Also, the results of the statistical parameters show a higher accuracy of the fitted function in the absence of selenium than in the presence of selenium.Also, the results showed water productivity in the presence of selenium was 17.81% higher than its value in the absence of selenium. It can be concluded that Selenium increases water productivity.