تأثیر محلول‌پاشی پتاسیم در کاهش اثرات مضر شوری در گیاه اسفناج (.Spinacia oleraceae L )

Introduction: Spinach is an important leafy vegetable in the cold season, and despite the fact that is considered as low-calorie food source contains significant amount of minerals such as iron, and vitamin A and C. According to the University of Utah 3.8 dS m-1 is salinity tolerance threshold for the spinach and yield decrease that have been reported by 10%, 25% and 50% at 5.5, 7 and 8 dS m-1 salinity. The necessity to supply adequate potassium has been demonstrated in salinity conditions. In salt stress conditions, foliar application of K in spinach, reduces the harmful effects of salt and increase the ratio of potassium to sodium (1.61 to 2.72). Foliar application of K with prevent of potassium transfer from root to shoot is causing continuation of photosynthesis and reduce the effects of salinity. Absorption of potassium from the leaves depends on the type of used compound. In this context, characteristics of plant (leaves with a waxy composition, duration of growth and leaf area) are important. 100 kg ha-1 of potassium in salt stress conditions by reducing the absorption of sodium, increased salt tolerance on the sunflower.
Materials and Methods: In order to evaluate the foliar application of K on the yield and yield components of spinach in salt stress condition, a study was conducted in 2012 by using split plot randomized based on complete block design with four replications at Isfahan Agricultural and Natural Resources Research Station. Three levels of irrigation water salinity consisted of a control (2 dS m-1), well water with salinity (4 dS m-1) and well water with salinity (8dS m-1) arranged in main plots and two levels of control and foliar applications of potassium fertilizer containing potassium oxide solubility in water (2.5 ml per liter) arranged in subplots. Statistical analysis was conducted by using SAS software and statistical tests were compared with Duncan at 5 percent.
Result and Discussions: The results showed that the yield of spinach with foliar application of K and 4 dS m-1 salinity was equaled 35300 kg ha-1 which had not significantly different from control treatment. Foliar application of K and 8 dS m-1 salinity, and also 8 dS m-1 salinity and without foliar potassium, had 20.2 and 38% yield reduction, respectively. In salinity 2.1, 4 and 8 dS m-1 plants m-2 were 40, 38.1 and 29.1, respectively. Leaf dry matter percent was improved with foliar application of K in 8 dS m-1 salinity. Effect of potassium, as modulators of salt in spinach, by researches of Shannon and Greve (24) and Kaya et al (14) have also been emphasized. Spinach leaves number was from 11.4 to 16.7 in different treatments. Foliar application of K in 4 and 8 dS m-1 salt treatment was increase in the number of leaves. This increased in treatment of 4 and 8 dS m-1 was 15.3 and 28.9 percent, respectively. In both saline treatments of 4 and 8 dS m-1, leaf length was positively affected by the application of potassium but in salinity 4 dS m-1 (unlike the eight salinity dS m-1) leaf width was not affected by the potassium spraying. The ability of plants to maintain intracellular potassium to sodium ratio leaves in certain extent is necessary for a salt tolerance. In fact, the application of potassium in salinity conditions by increasing the concentration of the K in organs is a kind of acclimation to the salt stress and activates repair mechanisms of the damage against of stress agent. The length of tail leaves in 4 dS m-1 salt was not significantly affected by the spraying of potassium while in 8 dS m-1 salinity, spraying potassium led to an increase of 28 percent in length of leaf tail. The effect of K application on the dry matter content in the 8 dS m-1 salinity was statistically significant. Potassium is the most abundant cation-forming in many plants (typically more than 10% of dry weight) and less than 10 grams per kg-1 of dry weight appear deficiency symptoms in most plants.
Conclusion: According to the results, in salinity conditions, the foliar application of K can be used as a factor to reduce the harmful effects of salinity. While the lack of fresh water for irrigation in arid and semi-arid crops has become a challenge, attention to the moderated mechanisms of the harmful effects of salt, is one of the approaches to face the challenges ahead.