industrial crops and products 27 ( 2 0 0 8 ) 315–321 available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/indcrop Effect of irrigation frequency and planting density on herbage biomass and oil production of thyme (Thymus vulgaris) and hyssop (Hyssopus officinalis) H.R. Khazaie a , F. Nadjafi b , M. Bannayan a,∗ a Ferdowsi University of Mashhad, College of Agriculture, Department of Agronomy, Mashhad, Iran b Shahid Beheshti University, Medicinal Plants and Drugs Research Institute, Tehran, Iran article info Article history: Received 28 August 2007 Received in revised form 20 November 2007 Accepted 25 November 2007 Keywords: Irrigation interval Planting density Medicinal plants Water saving abstract An experiment was undertaken to determine the herbage biomass and oil production of thyme (Thymus vulgaris Linn.) and hyssop (Hyssopus officinalis Linn.) in 2003 and 2004 in the semi-arid region of Khorasan in Iran. The experiment was a split plot with three irriga- tion intervals as main plots and three planting densities as subplots, all of which replicated three times. Irrigation intervals consisted of 7, 14, and 21 days for both crops and planting densities of 6.6, 8, and 10 (plants m -2 ) for thyme and 5, 6.6, and 8 (plants m -2 ) for hyssop. Dif- ferent planting densities were employed by changing planting distances on cultivation rows. Herbage biomass and oil production of shoots, harvested at flowering were measured as annual production of each crop. Irrigation intervals did not change total harvested herbage biomass and oil production of both crops. Averaged across both years of the experiment, thyme produced higher oil than hyssop. Both crops produced higher biomass and oil in the second year of the experiment compared to the first year. While thyme plants biomass and oil production were lower at the highest planting density, hyssop plants showed no response to planting density. Herbage biomass and oil production of hyssop did not show a clear trend in response to interaction of irrigation intervals and planting densities in both years of the experiment. Our results showed that there is a high potential for saving water through longer irrigation intervals (e.g. 14 days) using locally adapted plants in the semi-arid conditions of Khorasan. These crops serve as alternative sources of income in dry years. © 2007 Elsevier B.V. All rights reserved. 1. Introduction To meet agricultural demands and growing competition for water, a more effective use of water in both irrigated and rain- fed agriculture is essential. In regions where water scarcity is the principal limiting factor for cultivation, farmers are interested in growing crops that are able to adapt to drought conditions (Muchow, 1989; Bannayan et al., 2008). There are many farming communities within these regions which man- ∗ Corresponding author. Current address: Department of Biological and Agricultural Engineering, The University of Georgia, Griffin, GA 30223-1797, USA. Tel.: +1 770 229 3436; fax: +1 770 228 7218. E-mail address: Bannayan@uga.edu (M. Bannayan). age to survive under such conditions and, in some cases, even to succeed by exploiting natural resource bases, which their ancestors have used for generations (Reijntjes et al., 1992). Through a process of innovation and adaptation, tradi- tional farmers have developed numerous different indigenous farming systems finely tuned to many aspects of their environ- ment. Such risk management and adaptation strategies are in response to the limiting conditions of available water. Achiev- ing a high crop yield, under such conditions, depends on many 0926-6690/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.indcrop.2007.11.007