Effects of organic fertilizers on quantitative and qualitative traits of Mentha piperita L. under low water stress

To investigate the response of some quantitative and qualitative characteristics of peppermint (Mentha piperita L.) to organic fertilizers under low water stress, a factorial experiment was conducted in a randomized complete block design with three replications in the research farm of the Faculty of Agriculture of Urmia University in 2017-2018 crop year. Experimental treatments included organic fertilizer at five levels (control, cattle manure (20 ton ha-1), poultry manure (7 ton ha-1), vermicompost (10 ton ha-1), and compost (15 ton ha-1)) and soil moisture at three levels (50 (severe stress), 70 (moderate stress), and 90% (control: without stress) of field capacity). Low water stress decreased the content of leaf phosphorus or potassium, leaf phenols or flavonoids, and leaf relative water content and increased the leaf essential oil yield at full flowering stage. The highest amount of essential oil (1.58%) was observed under moderate stress conditions. Poultry manure and vermicompost significantly increased the amount of nitrogen, protein, and percentage of DPPH radical scavenging of leaves under low water stress compared to without stress conditions. The highest yield of essential oil (32.34 kg ha-1), stem dry weight (852.53 kg ha-1), leaf dry weight (1010.40 kg ha-1), and aerial parts dry weight (1863.93 kg ha-1) was obtained in the poultry manure treatment under optimal irrigation. Overall, organic fertilizers application under low water stress could be recommended to increase the plant yield and achieve sustainable agriculture.