Evaluation of humic acid application on biochemical composition and yield of black cumin under limited irrigation condition
Abstract
Black cumin is one of the oldest medicinal plants with scientific name of (Nigella sativa L.). Plants in their growth environment are constantly faced with numerous stresses that limit their chances to develop and survive in one way or another. Drought is one of the stress-producing factors that reduce crops production rate at the global level. Iran has an arid and semi-arid climate and its average rainfall is about one-third of the global average rainfall, so it is faced with drought stresses and periodic droughts. In order to study the effects of irrigation and humic acid on yield, yield components and essential oil composition of black cumin a field experiment was arranged as split plot based on a randomized complete block design with three replications during growing season of 2013- 2014. The experiment was conducted a farm located in agricultural research institute of Zabol university in east of Iran. Irrigation intervals (6, 9 and 12 days) and four levels of humic acid concentration (0, 1, 2 and 3 kg.ha-1) considered as in main plots and sub-plots, respectively. In this study, seed yield, essential oil percentage were measured and the chemical compositions of essential oil was determined by GC/MS. Results showed that limited irrigation had significant effects on seed yield. With application of humic acid increased seed yield, essential oil percentage, p-cymene, gama terpinene and thymoquinone. The highest of p-cymene 24.6% could be obtained from taking 3 kg.ha-1 humic acid and the lowest rate 15.4% was related to not applying humic acid. Also our results indicated that the seed yield ratio under limited irrigation was found to decrease in comparison with the control. According to the results, it appears that application of 3 kg.ha-1 humic acid was the best treatment in production of yield and essential oil of black cumin in this region.