Soil Properties and Yield of Peppermint (Mentha Piperita L.) in Response to Different Nitrogen Fertilizers Under Water-Deficit Conditions

Drought and lack of nutrients (including nitrogen) limit crop production in arid and semi-arid regions, including Iran. In order to investigate the combined effect of nitrogen fertilizer sources (organic and chemical) under low water stress on soil properties, biological yield and peppermint essential oil, a three-year experiment was conducted during the spring and summer of the years (2017-2019) in the semi-arid region of Iran. The experiment was conducted as split plots in the form of randomized complete blocks with three replications. Experimental treatments include three irrigation regimes (irrigation after draining 25, 40 and 55% of usable water in the root zone) as the main factor and six fertilizer treatments based on plant nitrogen requirements (100% Chemical, No fertilizer, 50% Chemical + 50% Azocompost, 100% Vermicompost, 100% Azocompost, 50% Chemical + 50% Vermicompost) as sub-factors. The results showed that water-deficit conditions decreased organic carbon, total nitrogen content, soil phosphorus and potassium and biological yield and increased the percentage of peppermint essential oil. Also, in most of the treatment compositions of irrigation regime, the application of organic fertilizer (especially pure vermicompost and azocompost treatments) or combination with chemical fertilizer the increase organic carbon, macronutrients (nitrogen and phosphorus) and micro (iron and zinc) in soil solution, causing improved biological yield and essential oil content and moderated the effects of water-deficit stress on peppermint. These practical measures can help save water and fertilizer consumption while promoting the production of healthy medicinal products over the course of three years.