Effects of Different Irrigation Management on Biomass and Essential Oil Production of Thymus vulgaris L., Salvia officinalis L. and Rosmarinus officinalis L., Cultivated in the Southern Sardinian Climate (Italy)

Thyme, sage and rosemary are crops which held an increasing importance for the essential oil production as cosmetic and food industry. These crops in Sardinia have a traditional cropping system based on a minimal irrigation water supply or a rainfed cultivation system. The modern irrigation approach, based on soil water content measurement and evapotranspiration evaluation is not considered yet. The three years trial (2006, 2007 and 2008) was carried out to better understand the irrigation requirement of these crops in open field cultivation. The experiment design consists of a complete randomized blocks with three replications and the irrigation strategies as controlled variability factor. The irrigation treatments used are: the no stress (NS) control treatment, the high stress (HS) irrigation, the medium stress (MS) irrigation, the aid irrigation (AI) extremely stressed and the Partial Root-zone Drying (PRD) obtained alternating the right side with the left side drip line, watering every fifteen days. It was determined the crop phenology, the quality and the quantity production parameters (biomass and essential oil content). There were both monitored the soil water content and the midday stem water potential (mSWP) as plant water stress indicator. The results show that different water saving irrigation strategies could have a strong significant influence and improve the fresh and dry biomass of the three crops. The oil content per 100 g of dry matter was affected by irrigation only on Salvia (two out of three years) and was higher in the AI treatment. The total oil content production of all the three crops was affected by irrigation treatments. AI, PRD and HS treatments resulted best as regards the water use efficiency, the essential oils production and the water saving.