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Background and Objectives: The importance of rapid, non-destructive, and accurate estimation of leaf area (LA) in agronomic and physiological studies is well known. The need for such estimates of leaf area in particular for leaves with unusual shapes has led to studies relating leaf dimensions and leaf area. However, a search of literature revealed that little information is available for short day onion (Allium cepa L.). The objective of this study was to develop a statistically validated regression model for leaf area prediction from simple non-destructive measurements for onion cultivated in the South of Iran. Materials and Methods: In order to prepare the required plant samples to measure leaf area parameters, an experiment was conducted in the cropping year 2020-2021 in a field of 300 square meters located in Hormozgan province-Rahdad district. The short-day cultivar Takii was used because of its wide planting area in the province. 40 leaves were chosen at random from plants growing in the farm, half were left for validation of the model and the other 20 leaves were subjected to measurement and calibration. The standard method (LICOR LI-3000C) was used for measuring the actual areas of the leaves. Before measuring the leaf area, two main parameters related to leaf length and width were accurately determined for each leaf. To select the best variables and the regression model for estimating leaf area, the fitted simple and multiple linear regression were subjected to the stepwise elimination method. Finally, the accuracy of the selected models was validated using the root mean square error (RMSE) and coefficient of determination (R2 ). Results: All linear models for estimation of leaf area with width (W) and length (L) as well as models including both variables were subjected to regression analysis. The results indicated that leaf length (L) is more appropriate variable for estimating onion leaf area and leaf width (W) was not able to properly describe leaf area. Based on the findings of this research leaf area estimation model with both W and L had the best prediction, with RMSE%=8.64, RMSE=1.76 and R2 =0.91. (Area=0.121 + 0.01537 L2 + 0.3225 L×W). Conclusion: As the understanding of plant growth and development has been increasing, such mathematical models will be very useful tools for the prediction of leaf area for many plants without the use of expensive devices. Thus, the models from the present study will enable researchers of plant growth modeling to predict leaf area non-destructively with the equations developed. [ABSTRACT FROM AUTHOR]

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.