The Effect of Different Levels of Manure, Urea and their Combination on Some Drought Resistance Physiological Traits of Moldavian balm (Dracocephalum moldavica L.) under Different Irrigation Regimes

Water deficit is one of the factors limiting the growth of plants in the world and is the most common environmental stress. Several studies show decreasing in growth, yield and plant death as a result of unfavorable water or water stress conditions. Management of nutrients consumption along with water consumption management influences the quantitative and qualitative yield of crops and medicinal plants. Although, chemical fertilizers provide plant nutrients for the plants faster and more effective, but to increase the quality of products, especially the medicinal and aromatic plants, the use of organic fertilizers is better than chemical fertilizers. Organic fertilizers cause decreasing in bulk density and increasing water retention in the soil. Manure is one of the organic fertilizer sources which its application is conventional in the sustainable management system of soil. Organic fertilizers, especially manures compare with chemical fertilizers having large amounts of organic materials and counted as a rich source of nutrients especially nitrogen, phosphorus and potassium which provide these elements over the time for the plants.

A split plot experiment was carried out in a randomized complete block design with three replications at the research farm of Shahrekord University. Main factor was three levels of irrigation regimes including: full irrigation (control), 75% and 50% of full irrigation while six levels of manure application including: 1) no amended fertilizer (control), 2) 25% urea + 75% manure 3) 50% urea + 50% manure 4) 75% urea + 25% manure 5) 100% urea and 6) 100% manure, were used as subplot. Water need of the other treatments was considered based on the water demand of control. Using the counter, the volume of required water was added to each plot. The period between two irrigations was determined using meteorological data and determining daily water requirement and the moisture regimes (water stress) was applied after the establishment of seedlings at eight leaf stage. Then at full flowering stage, the percentage of leaf water content (LWC), the amount of water to the dry weight (IWC), leaf water-retaining (RWP), water scarcity index of saturation (saturation deficit) (WSD), leaf relative water content (RWC), membrane stability (CMS), moisture retention capacity (MRC), relative water loss (RWL) and dry matter yield (DMY) were studied.

The results showed that the effect of irrigation regime on IWC, WSD, RWC, CMS and RWL was significant. The maximum IWC, RWC, CMS and RWL and the minimum WSD was observed in full water demand and 50% full irrigation treatments, respectively. Different fertilizer levels also showed significant effect on LWC, RWP, WSD, RWC, CMS, MRC, RWL and DMY. The interaction effect between irrigation regime and fertilizer was also significant on IWC, LWC, RWP, MRC, RWL and DMY. In general, in order to maintain the moisture balance of plant, application of 50% urea + 50% manure with supply of full water demand was recommended.

 Based on the results obtained at this experiment, it can be said that the complete water requirement caused increases in IWC, RWC, CMS, RWL and DMY, while the WSD was decreased. Moreover, application of 50% urea + 50% manure could increase LWC, RWP, MRC, RWL, IWC and DMY, reflecting the positive effect of fertilizers combined application. In total, according to the results of this research, in order to maintain the moisture balance of the plant, the combined application of manure and chemical fertilizers for 50% urea + 50% manure and supply of full water demand is recommended.