Meta-Analysis of Studies on the Effect of Nitrogen Fertilizer, Water Stress, And Density on the Quantitative and Qualitative Characteristics of Peppermint (Mentha Piperita L.)

How to bring together and interpret independent research studies is a fundamental question in all sciences. Using the meta-analysis technique allows researchers to gain more knowledge about the desired phenomena compared to a single or single study or intervention. In the past years, many studies have been conducted on the peppermint plant, which sometimes have contradictory results. Twenty English studies and 37 Persian research were chosen from a total of 250 studies following quality control. Lastly, a meta-analysis was conducted on 36 papers that included 283 effect sizes for water stress, chemical fertilizer (Nitrogen), and various planting densities on the quantitative and qualitative characteristics of peppermint. The impact of chemical fertilizers (Nitrogen) on the quantitative characteristics of biomass, dry weight, and plant height as well as the qualitative characteristics of oil yield, oil percentage, and oil constituents like menthone and limonene is shown in the meta-analysis results to be significant (P≥0.01). The menthol ingredient was negatively impacted by nitrogen chemical fertilizer, with no discernible effect (g = -0.408). The studies of the effects of chemical fertilizers (Nitrogen) on the studied traits have all been heterogeneous and asymmetric and confirm the use of the random model. Only the studies of the ingredients of the essential oil, i.e. limonene and linalool, are symmetric and show no diffusion error. Other studies require replication of studies for recommendation different planting densities have a considerable impact on all quantitative and qualitative features, with a rather homogenous and symmetric effect. (P<0.05). The plant's height yielded the largest effect size (g=1.108), while the oil percentage (g=0.564) produced the average effect size. Aside from oil percentage, other features are also significantly impacted by the heterogeneous and asymmetric effect of water stress. (P<0.05). An increase in the amount of essential oil is positively correlated with water stress. Furthermore, although studies do not demonstrate propagation mistakes, they have had a noteworthy and adverse impact on quantitative features. However, proline levels are positively and significantly impacted by water stress, and this effect is symmetrical. (P<0.05). The largest amount of positive effect obtained was on the amount of proline (g = 1.337) and the largest negative effect was related to plant height (g = -1.357). Meta-analysis allows us to examine and calculate its direction and strength with a more detailed and deeper investigation in addition to estimating the amount of impact.