Influence of Chemical Fertilizers and Animal Manure on Morphological Traits of Medicinal Plants in Northern IranJaber Mehdiniya Afra1*، Ebrahim habibi 1 ، Amin Fathi2، Ammara Saleem3Fatemeh Ghadimi4،Shima Khazainezhad4،Roghayeh Rezazadeh4،Tahmineh Danafar4،Yasaman Kheyri4،Fatemeh Nozari4،Zahra Avish41-Faculty of Agriculture, Technical and Vocational University, Tehran, Iran2-PhD of Agronomy, Islamic Azad University, Ayatollah Amoli Branch, Amol. Iran3-University of the Punjab, Lahore, Pakistan; ammara-602398@pu.edu.pk4-Associate student of Medicinal Plants Department, Tohid Amol Technical and Vocational School, Amol, Iran *Corresponding author Email: mehdiniya.jaber@gmail.comReceived: 10 April 2022 Accepted: 10 June 2022Abstract In 2022, we conducted a comprehensive investigation into the effects of chemical fertilizers and animal manure on three distinct medicinal plants. Employing a factorial experiment design with three repetitions, we examined the first factor - chemical fertilizers - at three distinct levels, comprising the recommended 100% NPK dosage as a control, 50% of the recommended NPK (NPK50), and 75% of the recommended NPK (NPK75). The second factor was animal fertilizers, which we studied at four levels: cow manure, sheep manure, chicken manure, and a control group. Notably, the highest dry weight of the entire peppermint plant, an impressive 22.98 g, was achieved through a treatment utilizing 75% of the recommended NPK in conjunction with chicken manure. Conversely, the lowest dry weight for the entire peppermint plant was recorded in the recommended 50% NPK treatment without the use of animal manure, yielding a mere 13.9 g. Lemon balm and zufa plants, under the recommended 100% NPK treatment without animal manure, displayed maximum dry weights of 18.18 and 5.07 g, respectively. In contrast, the lowest dry weight for these plants was observed in the recommended 50% NPK treatment without animal manure, with rates of 5.87 and 18.1 g, respectively. Our results demonstrated the positive impact of employing 100% of the recommended NPK fertilizer without animal manure on the growth of the studied plant organs. Conversely, by reducing the application of both chemical fertilizers and animal manure, the growth conditions of these plants were markedly improved, resulting in significant enhancements in various measured parameters. It is worth noting that an excessive influx of inputs did not lead to increased growth. Manuscript profile