تاثیر اوره بر برخی پاسخ‌های رشد و عناصر غذایی اسفناج (Spinacia Oleracea L.) در سطوح مختلف شوری خاک

به منظور بررسی پاسخ گیاه اسفناج رقم ’ویروفلی‘ به شوری در کاربرد با اوره در یک خاک دارای کمبود نیتروژن، آزمایشی در شرایط گلخانه ای به صورت فاکتوریل در قالب طرح کاملاً تصادفی با سه تکرار اجرا شد. تیمارها شامل چهار سطح شوری (بدون اعمال شوری، 1، 2 و 3 گرم کلرید سدیم بر کیلوگرم خاک، به ترتیب معادل قابلیت هدایت الکتریکی 0.7، 4.5، 8 و 11.5 دسی‌زیمنس بر متر در عصاره اشباع خاک) و پنج سطح نیتروژن (بدون کاربرد نیتروژن، 75، 150، 225، و 300 میلی‌گرم بر کیلوگرم خاک) از منبع اوره بود. اعمال شوری 4.5 و 8 دسی زیمنس بر متر اثر معنی داری (0.05≥p) بر عملکرد نسبی و سطح برگ اسفناج نداشت ولی شوری 11.5 دسی زیمنس بر متر نسبت به سطح بدون اعمال شوری و شوری 4.5 و 8 دسی زیمنس بر متر عملکرد نسبی و سطح برگ را به طور معنی داری (0.05≥p) کاهش داد. کاربرد نیتروژن اثر سوء شوری را بر عملکرد نسبی و سطح برگ کاهش داد. بیشترین و کمترین تغییرات محتوای آب اندام هوایی در شرایط شوری به ترتیب در سطح بدون کاربرد نیتروژن و در سطح 150 میلی گرم در کیلوگرم مشاهده شد. رگرسیون خطی نشان داد که در شوری 4.5 تا 11.5 دسی زیمنس بر متر بین عملکرد با نسبت کلر به نیتروژن اندام هوایی اسفناج یک رابطه منفی وجود دارد. کاربرد شوری و نیتروژن هم به صورت تنها و هم به صورت توام، نسبت k/na، ca/na و mg/na را کاهش داد. به طور کلی، کاربرد نیتروژن تا سطح متوسط می تواند اثرات منفی ناشی از شوری را در اسفناج بهبود دهد ولی استفاده بیش از حد معمول از کود نیتروژن نه تنها اثر مثبت نداشته بلکه ممکن است اثر منفی بر عملکرد گیاه داشته باشد.

Influence of Urea on Some Growth Responses and Nutrients of Spinach (Spinacia oleracea L.) under Different Levels of Soil Salinity

Introduction: Salinity is an environmental problem in the world, especially in arid and semiarid regions. High amounts of salts like sodium chloride (NaCl) in the soils and water have destructive effects on yield of plants. The harmful effects of salinity on plant growth are related to the low osmotic potential of the soil solution (water stress), the nutritional imbalance, the specific ion effect (salt stress), or the combination of these factors. The relationship between salinity and plant mineral nutrition is complicated. Under salinity stress, occurs the sodium and chlorine accumulation, resulting in ionic imbalance and the deficiency symptoms of nutrients in plants. The sodium (Na+) competes with the uptake of potassium (K+), calcium (Ca2+) and magnesium (Mg2+) by plant, and the chlorine (Cl) with the uptake of nitrates (NO3), phosphates (PO43) and sulfates (SO42).Materials and Methods: In order to evaluate the tolerance of spinach cv. “virofly” to salinity levels in application with different nitrogen rates, a greenhouse experiment was conducted as completely randomized design based on factorial arrangement with three replications at Shiraz University Agricultural Faculty. Treatments include four levels of salinity (without salinity, 1, 2 and 3 gr of sodium chloride per kg of soil, equivalents to 0.7, 4.5, 8 and 11.5 dS/m in saturated solution extract of soil, respectively), and five levels of nitrogen (unfertilized, 75, 150, 225 and 300 mg N/kg of soil) as urea source. Nitrogen treatments were applied in two installments in water soluble (half before planting and another half, 20 days after planting). In order to prevent sudden stress, saline treatments were applied gradually after complete plant establishment with irrigation water. The irrigation of the pots was carried out with distilled water and at field capacity. After 56 days of sowing, in every pot the spinach shoots were discarded near the surface of the soil and the required parameters were measured.Results and Discussion: The application of 4.5 and 8 dS/m salinity had no significant effect (≤0.05) on the relative yield and spinach leaf area, but 11.5 dS/m salinity significantly (≤0.05) decreased relative yield and spinach leaf area compared to without salinity level, 4.5 and 8 dS/m. Nitrogen application (75 and 150 mg/kg of soil) alleviated negative effect of salinity on yield and leaf area. Application of 225 and 300 mg N/kg of soil with 11.5 dS/m salinity significantly decreased the relative yield of spinach. The highest and lowest shoot water content changes in salinity conditions were observed in nonitrogen application and 150 mg N/kg application, respectively, which shows that the application of nitrogen in the medium level controls the water changes in the spinach plants. In this study, increasing the amount of nitrogen at all levels of salinity, elevated the shoot water content. The tolerant plant species in the face of environmental stresses maintain the water content of their cells in the higher levels. Therefore, it can be said that the maintenance of high leaf water content is an important mechanism for tolerance to salinity, and the cultivars that can hold more water in their leaves under stress conditions, will have more tolerance to salinity stress. Linear regression (R2 = 0.8198) showed that in the salinity levels of 4.5 to 11.5 dS/m, there is a negative relationship between the yield and the chlorine to nitrogen ratio (Cl/N) of spinach shoots, so that with increasing Cl/N, the spinach shoot yield decreased by gradient of 3.077. Application of nitrogen up to 225 mg/kg of soil gradually reduced the ratio of K/Na, Ca/Na and Mg/Na, however, the application of 300 mg N/kg of soil had no significant effect on these ratios. The application of different levels of salinity gradually reduced the K/Na, Ca/Na and Mg/Na ratio.Conclusion: The threshold of salinity of spinach cv. “virofly” was about 8 dS/m in our study, this was above the threshold mentioned (2 dS/m) for spinach in most sources. The application of nitrogen in medium level as urea can improve the negative effects of salinity in spinach but intensive nitrogen fertilization may increase the negative effects of salinity on plant yields.