Evaluation of Quantitative and Qualitative Traits of Hyssop (Hyssopus officinalis) under Heat Stress and Nitrogen Fertilizer (Case study: Sub Tropical Climatic Condition of Jiroft)

This study was performed to investigate some quantitative characteristics and quality of hyssop under heat stress and nitrogen fertilizer.

The experiment was conducted as a split-plot in a completely randomized block design with six planting dates and three replications in 2017-2018. The main factor was different levels of nitrogen fertilizer: 0, 50, 100 and 150 kg.ha-1 and sub-factor was planting dates between 30-day periods from October 17 to March 25.

Increasing nitrogen fertilizer at the level of 150 kg/ha resulted in the increase of 18.1%, 39.5%, 20.1%, 43.3% and 47.2% in flowering top-branch length, flowering top-branch weight, plant height, biomass yield and total essential oil yield, respectively, compared to not consumption. The highest yield of total essential oil (36051 g.ha-1) was obtained in T1N4, which was 89.7% higher than T4N1. Increasing ambient temperature in the range of 25–40 °C linearly led to decline of top-branch length, top-branch weight and biomass decreased but decreased essential oil yield in the above temperature range was fitted as a quadratic function (R2 = 0.86). Heat stress on delayed sowing dates T3, T4, T5 and T6 reduced the essential oil yield compared to the sowing date T1 by 30.5%, 70.3%, 66.4% and 39.3%, respectively.

The application of nitrogen fertilizer increased the studied traits. To reduce the effect of heat stress and achieve optimal yield, are recommended the hyssop planted from 25 October to 25 November and are used 150 kg.ha-1 of nitrogen fertilizer in the subtropical region of Jiroft.