الفهرس 
Introduction
Machanisms of water stressOnly 14 pages are availabe for public view
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Abstract
This investigation was carried out during the two seasons of 2007/2008 and 2008/2009 at the Experimental Station of Ornamental Plants, Fac. Agric. Mansoura Univ. to investigate the effect of water stress, humic acid foliar spray and potassium sulfate fertilizer as well as their interactions on some vegetative growth parameters, essential oil content and constituents in addition to chemical composition of marjoram plants (Majorana hortensis, L.). Mid. of November, 2007 and 2008, seeds of marjoram were sown in prepared nursery beds. After three months from sowing the seedlings were transplanted into 30 cm-diameter clay pots (one plant / pot) filled with soil mixture of clay and sand (2:1 v/v). The plants were held under natural conditions and irrigated as needed with fresh water for 8 weeks from transplanting date. Middle of April in both seasons, all plants treatments were started. The current research was included 18 interaction treatments which were arranged in split-split plot design. Water stress was assigned to the main plots as the plants were irrigated with fresh water at the rate of 100, 75 or 50% of field capacity. The sub plots were devoted to the spraying without or with humid acid (at the concentration of 1%). While, the sub-sub plots were allocated for potassium fertilization as the plants were fertilized with potassium sulfate at the rate of 0, 50 or 100 kg/fed. The plants were harvested three times in each season by cutting the aerial parts in the middle of June, August and October in both seasons. The obtained results can be summarized as following: I. Effect of water stress, humic acid, potassium fertilizer and their interaction on some vegetative growth parameters of marjoram plant: 1. The interaction treatment of irrigation rate at 100 % of field capacity plus spraying with humic acid and fertilization with 100 kg/fed potassium sulfate induced the highest values in all vegetative parameters compared to all other interaction treatments at the three cuts in the both seasons. II. Effect of water stress, humic acid, potassium fertilizer and their interaction on essential oil (%) and components of marjoram plant: 1. The interaction treatment of irrigation rate at 100 % of field capacity plus spraying with humic acid and fertilization with 100 kg/fed. potassium sulfate induced the highest values of essential oil (%) compared to all other interaction treatments at the three cuts in both seasons, whereas, the least values in this regard were recorded by the plants irrigated with 50% of field capacity, sprayed without humic acid and received 0 kg / fed potassium sulfate. 2. The interaction treatment of irrigation rate at 100% of field capacity plus spraying with humic acid and fertilization with 100 kg / fed potassium sulfate resulted in the highest values of α- pinene, β- pinene, myrcene and terpinene-4-ol at the three cuts in both seasons. III. Effect of water stress, humic acid, potassium fertilizer and their interaction on potassium (%) in the dry leaves of marjoram plant: 1. The interaction treatment of irrigation rate at 100 % of field capacity plus spraying with humic acid and fertilization with 100 kg / fed potassium sulfate induced the highest values of K (%) in the dry leaves compared to all other interaction treatments at the three cuts in both seasons, whereas, the least values in this regard were recorded by the plants irrigated with 50 % of field capacity, sprayed without humic acid and received 0 kg / fed potassium sulfate. Under the conditions of this experiment, irrigating marjoram plants once every four days at the rate of 100% of field capacity plus spraying with humic acid at the concentration of 1% and applying of potassium sulfate at the level of 100 kg / fed could be recommended to obtain the best results of plant height, plant fresh and dry weights, leaves dry weight, essential oil content and components as well as potassium content in dry leaves.