Effects of irrigation intervals on morphological characteristics of different Achillea millefolium L. populations

In order to investigate the effects of different irrigation intervals on morphological characteristics of different Achillea millefolium L. populations, an experiment was conducted at the experimental field of Research Institute of Forests and Rangelands during 2012 and 2013. Three irrigation intervals (7, 14 and 21 days) and 19 A. millefolium populations were compared in a factorial experiment based on a complete randomized block design with three replications. As many plants were lost in irrigation interval of 21 days, comparison was continued with irrigation intervals of 7 and 14 days. Results showed that irrigation intervals and population origins had significant effects (P≤0.005) on the plant height, crown diameter, stem number, dry matter yield (g plant
-1
), flower diameter, flower number and flowering time. In almost all populations the plant height, crown diameter and flower diameter decreased, whereas flower number per plant and the full flowering time increased in irrigation interval of 14 days. The 19 populations were grouped into three clusters. Populations in the cluster I had higher plant height, yield and flowering time. Populations in the cluster III showed higher crown diameter, flower diameter, stem number and flower number, and shorter full flowering time. These results indicated that populations in the cluster III had favorable potential production in semi-arid regions.