Effect of irrigation interval and water salinity on growth of vetiver (Vetiveria zizanioides)

The purpose of the present study was to investigate the limits of irrigationwater salinity and soil water content for growth inhibition of vetiver. Moreover,different models were studied to describe the root water uptake and plant topgrowth under salinity and water stresses in a pot experiment. Irrigation treatmentsconsisted of three irrigation intervals (3, 6 and 9-day). The salinity levels of theirrigation water were 0.8 (tap water), 10, 20 and 30 dS m-1. It is concluded that byenforcing salinity and increasing its level up to 30 dS m-1, no significant declinein the top dry matter (TDM) has been observed. However, in the salinity level of30 dS m-1 increasing of soil water stress caused TDM to decrease. The maximumamount of leaf area index (LAI) was observed at water salinity level of 0.8 dS m-1and as the salinity increased, it decreased. However, at different water salinitylevels, the reduction of LAI was not significant. Moreover, the results showedthat the water stress did not have significant effects on reduction of LAIseparately, while the water salinity did. The thresholds of water salinity andirrigation intervals for affecting vetiver's root were between 20 and 30 dS m-1 and6 days (80% soil available water depletion), respectively. Moreover, thethreshold values of soil salinity were 13.8 dS m-1 for top and 19.4 dS m-1 for rootgrowth. Then, it can be concluded that the top growth is more sensitive to thewater salinity, than the root one. Therefore, in terms of economic, if using root ismore substantial, root production would be more beneficial. The growthreduction per unit increase in soil salinity for top growth and root growth are 2%and 3% per dS m-1, respectively. Therefore, top and root growth affectedsimilarly by increasing the soil salinity. Relative yield response factor to waterstress was 0.472 that showed the vetiver resistance to soil water stress. It is "> indicated that the root water uptake coefficient (α) was predicted accurately afterconsidering the results and comparing different models. Furthermore, theestimated values of α predicted the shoot dry weight accurately. However,Homaee and Feddes method is preferred for estimation of TDM