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

Document Type : Research Article


1 Payame Noor University

2 Tehran University

3 Shiraz University


Introduction: Salinity is an environmental problem in the world, especially in arid and semi-arid 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 no-nitrogen 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.


1- Ashraf M., and Harris P.J.C. 2004. Potential biochemical indicators of salinity tolerance in plants. Plant Science 166: 3-16.
2- Boh M.Y., Germer J., Müller T., and Sauerborn J. 2013. Comparative effect of human urine and ammonium nitrate application on maize (Zea mays L.) grown under various salt (NaCl) concentrations. Journal of Plant Nutrition and Soil Science 176: 703-711.
3- Chen W., Hou Z., Wu L., Liang Y., and Wei C. 2010. Effects of salinity and nitrogen on cotton growth in arid environment. Plant and Soil 326: 61-73.
4- Debez A., Hamed K.B., Grignon C., and Abdelly C. 2004. Salinity effects on germination, growth, and seed production of the halophyte Cakile maritima. Plant and Soil 262: 179-189.
5- Elgharably A., Marschner P., and Rengasamy P. 2010. Wheat growth in a saline sandy loam soil as affected by N form and application rate. Plant and Soil 328: 303-312.
6- Esmaili E., Kapourchal S.A., Malakouti M.J., and Homaee M. 2008. Interactive effect of salinity and two nitrogen fertilizers on growth and composition of sorghum. Plant and Soil Environment 54(12): 537-546.
7- Imami A. 1996. Plant analyses methods. Soil and Water Research Institute. vol 1. Journal No.982. (In Persian)
8- Irshad M., Eneji A.E., Khattak R.A., and Khan A. 2009. Influence of nitrogen and saline water on the growth and partitioning of mineral content in maize. Journal of Plant Nutrition 32: 458-469.
9- Irshad M., Yamamoto S., Eneji A.E., Endo T., and Honna T. 2002. Urea and manure effect on growth and mineral contents of maize under saline conditions. Journal of Plant Nutrition 25: 189-200.
10- Khalil M.A., Fathi A., and Elgabaly M. 1967. A salinity-fertility interaction study on corn and cotton. Soil Science Society of America, Proceedings 31: 683-686.
11- Kumar V., Shriram V., Nikam T.D., Jawalib N., and Shitole M.G. 2008. Sodium chloride-induced changes in mineral nutrients and proline accumulation in "indica" rice cultivars differing in salt tolerance. Journal of Plant Nutrition 31: 1999-2017.
12- Langdale G.W., Thomas J.R., and Littleton T.G. 1971. Influence of soil salinity and nitrogen fertilizer on spinach growth. Journal of the Rio Grande Valley Horticultural Society 25: 61-66.
13- Levitt J. 1980. Responses of plants to environmental stresses: Water, radiation, salt and other stresses. Vol. II. Academic Press, New York.
14- Martinez V., and Cerda A. 1989. Influence of nitrogen source on rate of Cl, N, Na, and K uptake by cucumber seedlings grown in saline conditions. Journal of Plant Nutrition 12: 971-983.
15- Momeni A.S. 2010. Geographical distribution and salinity levels of Iran's soil resources. Journal of Soil Research (Soil and Water Science) 24(3): 215-203. (In Persian)
16- Munns R. 1993. Physiological process limiting plant growth in saline soil: some dogmas and hypotheses. Plant, Cell and Environment 16: 15-24.
17- Ranjbar G.h., and Pirasteh-Anosheh H. 2015. A glance to the salinity research in Iran with emphasis on improvement of field crops production. Iranian Journal of Crop Sciences 17(2): 165-178. (In Persian with English abstract).
18- Razavi Nasab A., Tajabadi Pour A., and Shirani H. 2014. Effect of salinity and nitrogen application on growth, chemical composition and some biochemical indices of pistachio seedlings (Pistacia vera L.). Journal of Plant Nutrition 37(10): 1612-1626.
19- Rogers M.E., Grieve C.M., and Shannon M.C. 2003. Plant growth and ion relations in lucerne (Medicago sativa L.) in response to the combined effects of NaCl and P. Plant and Soil 253: 187-194.
20- Sadeghi Pour Marvi M. 2010. Nitrogen use efficiency of spinach. Journal of Water and Soil 24(2): 244-253. (In Persian with English abstract)
21- Saura-Mas S., and Lloret F. 2007. Leaf and shoot water content and leaf dry matter content of mediterranean woody species with different post-fire regenerative strategies. Annals of Botany 99: 545-554.
22- Shannon M.C., and Grieve C.M. 1999. Tolerance of vegetable crops to salinity. Scientia Horticulturae 78: 5-38.
23- Shannon M.C., Grieve C.M., Lesch S.M., and Draper J.H. 2000. Analysis of salt tolerance in nine leafy vegetables irrigated with saline drainage water. Journal of the American Society for Horticultural Science 125(5): 658-664.
24- Singh M., Singh V.P., and Prasad S.M. 2016. Responses of photosynthesis, nitrogen and proline metabolism to salinity stress in Solanum lycopersicum under different levels of nitrogen supplementation. Plant Physiology and Biochemistry 109: 72-83.
25- Singh S.K., Sharma H.C., Goswami A.M., Datta S.P., and Singh S.P. 2000. In vitro growth and leaf composition of grapevine cultivar as affected by sodium chloride. Biologia Plantarum 43(2): 283-286.
26- Soliman M.S., Shalabi H.G., and Campbell W.F. 1994. Interaction of salinity, nitrogen, and phosphorus fertilization on wheat. Journal of Plant Nutrition 17: 1163-1173.
27- Villa-Castorena M.A., Ulery L., Catalan-Valencia E.A., and Remmenga M.D. 2003. Salinity and nitrogen rate effects on the growth and yield of chile pepper plants. Soil Science Society of America Journal 67: 1781-1789.
28- Xu C., and Mou B. 2016. Responses of spinach to salinity and nutrient deficiency in growth, physiology, and nutritional value. Journal of the American Society for Horticultural Science 141(1): 1-10.
29- Yasuora H., Tamira G., Steina A., Cohen S., Bar-Tal A., Ben-Gala A., Yermiyahua U. 2017. Does water salinity affect pepper plant response to nitrogen fertigation? Agricultural Water Management 191: 57-66.
30- Yin X., McClure M.A., and Hayes R.M. 2011. Improvement in regression of corn yield with plant height using relative data. Journal of Science and Food of Agriculture 91: 2606-2612.
  • Receive Date: 09 April 2019
  • Revise Date: 19 January 2021
  • Accept Date: 19 December 2020
  • First Publish Date: 05 January 2021