International Research Journal of Applied and Basic Sciences. Vol., 3 (4), 770-777, 2012 Available online at http://www. irjabs.com ISSN 2251-838X ©2012 Growth and macro and micronutrients concentration in spinach (Spinacia oleracea L.) as influenced by salinity and nitrogen rates Jamal Sheikhi 1* and Abdolmajid Ronaghi 1 1 Department of Soil Science, College of Agriculture, Shiraz University, Shiraz, Iran. * Corresponding author. Email: sheikhi.jamal@yahoo.com ABSTRACT: Salinity and nitrogen (N) deficiency are growth limiting factors for most plants including spinach in arid and semiarid areas. A greenhouse experiment was conducted to evaluate the effect of salinity levels and N rates on growth and concentration of macro and micronutrients in spinach aerial parts. Treatments included four salinity levels 0 (S0), 1000 (S1), 2000 (S2) and 3000 (S3) mg NaCl kg -1 of soil and five N rates 0, 75, 150, 225 and 300 mg N kg -1 of soil as urea. Results showed that shoot dry matter yield (DMY) of spinach decreased at S3 compared to those of S0, S1 and S2. Increasing N rates up to 225 mg kg -1 significantly increased DMY. Addition of NaCl increased concentrations of N, phosphorus (P), zinc (Zn), copper (Cu), sodium (Na) and chlorine (Cl), but decreased those of potassium (K), iron (Fe) and magnesium (Mg) in spinach aerial parts. Increasing NaCl levels, at 300 mg N rate, increased concentration of calcium (Ca) but decreased that of manganese (Mn) in spinach shoot. Application of N rates increased concentration of N, Ca, Mg, Cu and Na in spinach shoot. Iron concentration decreased in shoot at 75 mg N level compared to that of control. Application of N up to 150 mg significantly increased Mn concentration, while decreased that of Cl in spinach shoot. Detrimental effects of salinity at S3 level on the reduction of DMY increased at 225 and 300 mg N rates compared to lower rates of N and salinity. Spinach is considered as a moderately salt sensitive leafy vegetable that tolerance threshold is 2 dS m -1 , however; our results indicated that tolerance threshold for Virofly cultivar was at least 8 dS m -1 , therefore, it might be considered as a moderately salt tolerant spinach cultivar. In conclusion, over fertilization of N aggravated detrimental effect of salinity on the growth of spinach. Keywords: over fertilization, NaCl, nutrients concentration, spinach INTRODUCTION High salts concentration inhabit plant growth through osmotic pressure, ionic imbalance, and specific ion toxicity (Cornillon and Palloix, 1997). The relationships between salinity and mineral nutrition of plants are complicated and not well understood. Among the essential elements, nitrogen (N) is usually the most growth limiting plant nutrient in saline or non-saline soils (Irshad et al., 2002) and an important element for economic vegetable production (Yoldas et al., 2008). Application of N fertilizers in saline soils might decrease the detrimental effects of salinity on plant growth (Soliman et al.,  bassam, 2001). However, over fertilization with N may contribute to soil salinization and increase the negative effects of salinity on plant growth (Villa-Castorena et al., 2003). This effect depends upon the salinity level, composition of salts, the plant species and environmental factors (Grattan and Grieve, 1999). Accumulation of Na + and Cl - more occurs under salinity stress, resulting in ionic imbalances and nutrient deficiency symptoms in plants, as Na + competes with K + , Ca 2+ , Mg 2+ , and Mn 2+ , while Cl  restricts the uptake of NO 3  , H 2 PO 4  and SO 4 2 (Kumar et al., 2008). Effect of N fertilization on nutrient concentration in plant shoots can vary according to plant type and N rates. Spinach is greatly responsive to N fertilization (Cantliffe, 1992), and is a moderately salt sensitive leafy vegetable that tolerance threshold is 2 dS m -1 (Shannon and Grive, 1999). The objective of present study was to evaluate the effects of salinity and nitrogen rates on the growth and concentration of macro and micronutrients in spinach.