Assessment of morpho-physiological and quantitative and qualitative yield of Peppermint (Mentha piperita L.) under different irrigation regimes and application of different nitrogen fertilizer

Water and nitrogen fertilizer are major determinants of the level of agricultural production in the world, in addition to the quantity and quality of Medicinal plants are also effective. Iran's climate is mainly dry and semi-arid, in such a situation, where abnormal environmental stresses occur for plants. Improving crop yields in these stress conditions require good management of inputs (such as water and nutrients), their amount and type, and knowledge of physiological processes and plant defense mechanisms is essential. Water stress can significantly alter the metabolism of plants and reduce growth and photosynthesis and ultimately yield of plants. In this situation, effective management of water consumption in agriculture is an urgent necessity. In this regard, the use of agronomic techniques such as application of organic fertilizers or enhancement of soil biological conditions may be effective in reducing the effects of water stress and less use of chemical fertilizers for sustainable agriculture and human nutritional health. Also, intensive agriculture with the widespread use of chemical fertilizers, especially nitrogen can cause an increase in costs and environmental pollution. A key component of sustainable agriculture is use of organic fertilizers such as vermicompost and azocompost.

In order to investigate the effects of water deficit stress and different nitrogen fertilizers on morphological, physiological traits, biological yield and essential oil percentage of peppermint, a experiment was conducted in a factorial arrangement in a randomized complete block de sign with three replications were carried out in 2018 at the field research station of the Agricultural Research Center of Tarbiat Modares University in Karaj (51 10’E, 33 44’ N, 1305.2 m above sea level). Experimental treatments consisted of three irrigation regimes (irrigation up to field capacity and after unloading 25, 40 and 55% water use in root zone, respectively) as the major factor and six fertilizer treatments based on nitrogen requirement respectively (100% chemical fertilizer, no fertilizer, 50% chemical + 50% azocompost, 100% vermicompost, 100% azocompost and 50% chemical fertilizer + 50% vermicompost) were as sub-factors. After field preparations, this area was divided into 54 experimental plots each of which were 2 m long with six rows, 0.2 m apart. Between all the main plots, a 3 m alley was kept to eliminate the influence of lateral water movement. Plant to plant distance in each row was 0.2 cm.

Analysis of variance showed that the effect of all the experimental treatments and their interaction on all measured traits was significant. The results showed that mild and severe drought stress decreased plant height (18.2 and 42.92%) and biological yield (15.11 and 51.98%, respectively), while pigment, carotenoid, anthocyanin, proline and essential oil percentage increased. Nitrogen fertilizer application increased all measured traits. In most of the traits measured in this experiment, 50% chemical fertilizer and 50% vermicompost fertilizer were evaluated even better under severe water deficit conditions than other treatments.

The results also showed that if the aim of planting peppermint is to improve the quality (essential oil percentage) of the plant by applying high water deficit stress, it can save more than 50% water consumption by producing the highest essential oil percentage. And vermicompost fertilizer can also be substituted for nitrogen chemical fertilizer to promote safe and sustainable
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