تعيين حد آستانۀ كاهش عملكرد ريحان و ارزيابي مدل‌هاي جذب آب تحت شرايط تنش شوري

آب و خاک  

دوره 30 - شماره 1

نوع مقاله: Original Article
چكيده: شوري منابع آب و خاك از چالش‌هاي مهم بخش كشاورزي در ايران است. در زمينه چگونگي پاسخ گياهان به تنش‌ شوري، چند مدل‌ رياضي وجود دارد. ليكن اغلب اين مدل‌ها در شرايطي خاص كاربرد دارند. هدف از اين پژوهش، برآورد آستانۀ كاهش عملكرد ريحان، مدل‌سازي واكنش گياه ريحان به شوري و نيز ارزيابي كارآيي مدل‌هاي رياضي موجود در برآورد عملكرد اين گياه بود. به همين منظور، آزمايشي با ۱۳سطح مختلف شوري شامل شوري‌هاي 1.2، 1.8، 2، 2.2،2.5، 2.8، 3، 3.5، 4، 5، 6، 8 و 10 دسي‌زيمنس بر متر انجام شد. تيمارهاي شوري با استفاده از اختلاط آب رودخانه شور با آب شرب تهيه شد. به منظور كمّي كردن اثر شوري بر عملكرد محصول، از هفت مدل‌ رياضي استفاده شد. نتايج نشان داد آستانه كاهش عملكرد ريحان نسبت به شوري خاك ۲۵/۲ دسي‌زيمنس بر متر و شيب خط كاهش عملكرد، 7.2 درصد بر دسي‌زيمنس بر متر مي‌باشد. مدل ون‌گنوختن و هافمن (۴۸) در شبيه‌سازي تابع كاهش عملكرد ريحان به شوري عصاره اشباع دقتي بيشتر نسبت به ديگر مدل‌ها داشت. به طور كلي، نتايج اين پژوهش نشان داد كه مدل‌هاي ون‌گنوختن و هافمن (۴۸)، استپوهن و همكاران (۴۴) و همايي و همكاران (۱۳) براي شبيه‌سازي واكنش عملكرد ريحان به شوري عصاره اشباع خاك از دقتي مناسب برخوردارند.
Determining the Threshold Value of Basil Yield Reduction and Evaluation of Water Uptake Models under Salinity Stress Condition
Article Type: Original Article
Abstract: Introduction: Several mathematical models are being used for assessing the plant response to the salinity of the root zone. The salinity of the soil and water resources is a major challenge for agricultural sector in Iran. Several mathematical models have been developed for plant responses to the salinity stress. However, these models are often applicable in particular conditions. The objectives of this study were to evaluate the threshold value of Basil yield reduction, modeling Basil response to salinity and to evaluate the effectiveness of available mathematical models for the yield estimation of the Basil .
Materials and Methods: The extensive experiments were conducted with 13 natural saline water treatments including 1.2, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.5, 4, 5, 6, 8, and 10 dSm-1. Water salinity treatments were prepared by mixing Shoor River water with fresh water. In order to quantify the salinity effect on Basil yield, seven mathematical models including Maas and Hoffman (1977), van Genuchten and Hoffman (1984), Dirksen and Augustijn (1988), and Homaee et al., (2002) were used. One of the relatively recent methods for soil water content measurements is theta probes instrument. Theta probes instrument consists of four probes with 60 mm long and 3 mm diameter, a water proof container (probe structure), and a cable that links input and output signals to the data logger display. The advantages that have been attributed to this method are high precision and direct and rapid measurements in the field and greenhouse. The range of measurements is not limited like tensiometer and is from saturation to wilting point. In this study, Theta probes instrument was calibrated by weighing method for exact irrigation scheduling. Relative transpiration was calculated using daily soil water content changes. A coarse sand layer with 2 centimeters thick was used to decrease evaporation from the surface soil of the pots. Quantity comparison of the used models was done by calculating statistical indices such as maximum error (ME), normalized root mean square error (nRMSE), modeling efficiency (EF), and coefficient of residual mass (CRM). At the end of the experiment, dry matter yield at the different treatments was measured and relative yield was calculated by dividing dry matter yield of treatments on dry matter yield at no stress treatment (control treatment). Leaching requirement in experimental treatments was calculated by Ayarset al., (2012) equation.
Results and Discussion: The results indicated that Basil threshold value based on soil salinity was 2.25 dSm-1 with the yield reduction of 7.2% per dSm-1. The mathematical model of van Genuchten and Hoffman (1984) had a higher precision than other models in simulating Basil yield reduction function based on saturated soil extract salinity. The overall observations revealed that van Genuchten and Hoffman (1984), Steppuhnet al., (2005) and Homaeeet al., (2002) models were accurate for simulating Basil root water uptake and yield response to saturated soil extract salinity. Considering the presented results, it seems that among math-empirical models for salinity stress conditions, model of van Genuchten and Hoffman (1984) is more accurate than Maas and Hoffman (1977), Dirksen and Augustijn (1988) and Homaeeet al., (2002a) models. The works of Green et al., (2006) and Skaggs et al., (2006) came to the same conclusion. Our work indicated that mostly statistical models have lower precision than math-empirical models. Steppuhn et al., (2005a) reported that statistical models had the higher accuracy than math-empirical model of Maas and Hoffman (1977) and among statistical models, the modified Weibull model had the best fit on measured data which is in good agreement with the results of this study.
Conclusion: The goals of this research were to evaluate Basil response to saturated soil extract salinity, to estimate threshold value of Basil crop coefficients, to obtain yield reduction gradient, and also to investigate efficiency of available math-empirical models in estimating reduction functions. The results of this study indicated that the Basil threshold value obtained based on saturated soil extract salinity was 2.25 dSm-1 and the gradient of yield reduction was 7.2% per dSm-1 according to Maas and Hoffman (1977) linear fitting. The reached general conclusion was that among the math-empirical reduction functions, the model of van Genuchten and Hoffman (1984) had the highest accuracy when compared to the models of Maas and Hoffman (1977), Dirksen and Augustijn (1988) and Homaee et al., (2002a). Therefore, it is recommended to use the van Genuchten and Hoffman (1984), Steppuhn et al., (2005), and Homaee et al., (2002) models respectively, instead of the other models in this research.
قیمت : 20,000 ريال