تاثیر شکل نیتروژن بر ترکیب شیمیایی و عملکرد ارقام کاهو (Lactuca Sativa L.) در کشت بدون خاک

شکل نیتروژن (نیترات و آمونیوم) محلول غذایی مورد استفاده در کشت های بدون خاک بر رشد و ترکیب شیمیایی کاهو موثر است. از طرف دیگر ارقام مختلف کاهو پاسخ های متفاوتی نسبت به شکل نیتروژن محلول غذایی نشان می دهند. این پژوهش به منظور بررسی تاثیر شکل نیتروژن بر ترکیب شیمیایی و عملکرد ارقام کاهوی رومین به صورت کشت بدون خاک انجام شد. این آزمایش به صورت فاکتوریل در قالب طرح کاملاً تصادفی با دو عامل نسبت آمونیوم به نیترات و نوع رقم در سه تکرار در گلخانه تحقیقاتی دانشگاه شهرکرد روی گیاه کاهو انجام شد. نسبت آمونیوم به نیترات محلول غذایی شامل 5 سطح 0:100، 15:85 با و بدون بازدارنده نیترات سازی dmpp و 30:70 با و بدون بازدارنده نیترات سازی dmpp بود. ارقام کاهوی مورد استفاده نیز شامل دو رقم ترسا4 و کالیفرنیا5 بودند. نتایج نشان داد کاربرد 30 درصد کل نیتروژن محلول غذایی به صورت آمونیوم منجر به افزایش معنی‌دار غلظت فسفر بخش هوایی در رقم کالیفرنیا (به میزان 40 درصد)، کاهش معنی دار غلظت پتاسیم بخش هوایی (به میزان 27.3 و 14.8 درصد به ترتیب در ارقام ترسا و کالیفرنیا) و کلسیم بخش هوایی (به میزان 42.0 و 31.1 درصد به ترتیب در ارقام ترسا و کالیفرنیا) در مقایسه با عدم کاربرد آمونیوم شد. بیشترین وزن تر بخش هوایی کاهو در رقم ترسا (334 گرم بر گلدان) با کاربرد نسبت 0:100 آمونیوم به نیترات و در رقم کالیفرنیا (435 گرم بر گلدان) با کاربرد نسبت 15:85 آمونیوم به نیترات حاصل شد. کاربرد بازدارنده نیترات سازی dmpp تاثیر معنی داری بر وزن تر و خشک بخش هوایی و غلظت فسفر، پتاسیم و مس بخش هوایی هر دو رقم کاهو در نسبت های 15:85 و 30:70 آمونیوم به نیترات در مقایسه با عدم کاربرد نداشت. برمبنای نتایج این پژوهش کاربرد نسبت های 0:100 و 15:85 آمونیوم به نیترات به ترتیب در ارقام ترسا و کالیفرنیا برای تولید در شرایط مشابه این پژوهش قابل توصیه است.

The Effect of Nitrogen Form on Chemical Composition and Yield of Lettuce (Lactuca sativa L.) Cultivars in Soilless Culture

Introduction: Ammonium (NH4+) and nitrate (NO3) ions are the two main forms of nitrogen (N) for plants. But, they influence differently on growth and chemical composition of plants. The effect of N form on plant growth depends on plant species, development stage of plant, pH, and temperature, ratio of NH4+ /NO3 and nitrogen level of nutrient solution. Lettuce is one of the leafy vegetables that has been cultivated in soilless culture in many greenhouses in the world. This plant can respond well to NH4+ nutrition, but the information about optimum NH4+/NO3 ratio in the nutrient solution and respond of lettuce cultivars to partial replacement of NO3 by NH4+ is scarce. Application of nitrification inhibitors such as 3, 4dimethylpyrazole phosphate (DMPP) with ammonium fertilizers lead to high Nuse efficiency as well as reducing denitrification and leaching losses. Nitrification inhibitors are compounds that delay the biological oxidation of ammonium to nitrite by depressing the activity of Nitrosomonas bacteria. This study was conducted to elucidate the effect of nitrogen form (NNO3− and NNH4+) and the use of a nitrification inhibitor (DMPP) on chemical composition and yield of lettuce (Lactuca sativa L.) cultivars in research greenhouse of Shahrekord University.;Materials and Methods: A factorial experiment using completely randomized design was carried out with two factors of NH4+/NO3 ratio (0:100, 15:85 with and without DMPP, 30:70 with and without DMPP) and lettuce cultivars (Teresa and California) with three replications under hydroponic conditions. Lettuce plants were grown in 1.7 L plastic pots (one plant per pot) and the substrate used was mixture of cocopeat + perlite with ratio of 2:1 (v/v). Different nutrient solutions were applied by hand two or three times per week to obtain a leaching fraction of 5 to 20%. After seven weeks plants were harvested, fresh weight of shoots and roots were determined and plants were dried in an oven at 60 °C. Then, dry weight of shoots and roots were measured and plants were ground for nutrient analysis including of P, K, Ca, Mg, Fe, Mn, Zn and Cu. ;Results and Discussion: The results showed that application of nutrient solution with NH4+/NO3 ratio of 30:70 in California cultivar and 15:85 in Teresa cultivar led to significant increase shoot P concentration compared with the 0:100 of NH4+/NO3 ratio (40 and 13%, respectively). This was due to synergistic effect of NH4+ on the uptake of P by roots. In both Teresa and California cultivars, replacing 30% NO3 in the nutrient solution with NH4+ resulted to significant decrease shoot K concentration (27.3 and 14.8% in Teresa and California cultivars, respectively) as well as shoot Ca concentration (42.0 and 31.1% in Teresa and California cultivars, respectively) compared with the 0:100 of NH4+/NO3 ratio. This decrease is related to antagonistic effects of NH4+ on the uptake of K and Mg by roots. In Teresa cultivar, increasing the NH4+/NO3 ratio to 15:85 led to the meaningful increase of shoot Fe (97%), Mn (68%) and Zn (54%) concentration in comparison with 0:100 of NH4+/NO3 ratio. But, in California cultivar shoot Mn concentration increased (65%) with 30% replacement of NO3 by NH4+. This means that changing NH4+/NO3 ratio in the nutrient solution is an excellent approach to control the relative uptake of cations and anions by the plant. The greatest quantity of shoot fresh weight in Teresa (334 g pot1) and California (435 g pot1) cultivars were obtained from 0:100 and 15:85 of NH4+/NO3 ratios, respectively. The current study indicates that the lettuce cultivars respond differently to the form of N supply. There is a genotypic variability in the ability of plants to supply carbon skeletons for NH4+ assimilation in the roots. Thus, California cultivar is a genotype sensitive to enhanced ammonium nutrition and Teresa cultivar is a genotype insensitive to enhanced ammonium nutrition. Increasing the NH4+/NO3 ratio to 30:70 led to the meaningful decrease (42%) of root fresh weight in comparison with nutrient solution without NH4+. Application of nitrification inhibitor DMPP with the NH4+/NO3 ratios of 15:85 and 30:70 had not significant effect on the shoot fresh and dry weight as well as the concentration of P, K and Cu in the shoot of both lettuce cultivars in comparison to these ratios without DMPP.;Conclusion: The results suggest that the NH4+/NO3 ratios of 0:100 and 15:85 can be recommended for production of Teresa and California lettuce cultivars under the conditions of the present study, respectively.