اثر نيتروژن بر كارايي مصرف تشعشع و شاخص‏هاي رشد ارقام مختلف ذرت (Zea mays L.) تحت شرايط كرمانشاه

The effect of Nitrogen on Radiation Use Efficiency and Growth indices of Maize Hybrids (Zea mays L.) under Kermanshah Condition

كارایی مصرف تشعشع یك راه‌كار مؤثر برای كمی كردن تجمع ماده خشك است كه به شدت متأثر از نوع گونه گیاهی، شرایط آب و هوایی و مدیریت زراعی است. بنابراین، پژوهش حاضر با هدف بررسی اثر نیتروژن بر كارایی مصرف تشعشع، شاخص‏های رشد و عملكرد برخی از ارقام رایج ذرت اجرا شد. آزمایش به‌صورت كرت‏های خرد شده در قالب طرح پایه بلوك‌های كامل تصادفی با چهار تكرار در سال 1393 اجرا شد. تیمارهای آزمایش شامل چهار سطح كود نیتروژن (138، 238، 350 و 483 كیلوگرم اوره در هكتار) در كرت‏های اصلی و سه رقم ذرت 704، سیمون و 678BC در كرت‏های فرعی قرار گرفتند. نتایج نشان داد بیشترین و كمترین شاخص سطح برگ، دوام سطح برگ، سرعت رشد محصول و عملكرد ماده خشك كل به‌ترتیب در ارقام 704 و 678BC مشاهده گردید. با افزایش میزان كاربرد كود نیتروژن از 138 به 238، 350 و 483 كیلوگرم اوره در هكتار كارایی مصرف تشعشع به‌ترتیب با حدود 13، 21 و 22 درصد افزایش از 33/2 به 63/2، 81/2 و 84/2 گرم بر مگاژول تشعشع فعال فتوسنتزی بهبود یافت. با این وجود ارقام ذرت از نظر كارایی مصرف تشعشع تفاوت معنی‏داری با یكدیگر نداشتند. بررسی همبستگی بین كارایی مصرف تشعشع و صفات شاخص‏های رشد ذرت نیز نشان داد كه همبستگی مثبت و معنی‏داری بین كارایی مصرف تشعشع و حداكثر شاخص سطح برگ، دوام سطح برگ، حداكثر جذب تشعشع، حداكثر سرعت رشد محصول، حداكثر سرعت رشد نسبی و حداكثر ماده خشك كل وجود داشت. بیشترین عملكرد ماده خشك كل (20450 كیلوگرم در هكتار) مربوط به رقم 704 و شرایط مصرف 483 كیلوگرم اوره در هكتار بود. رقم سیمون در شرایط مصرف 483 كیلوگرم اوره در هكتار نسبت به ارقام دیگر از عملكرد دانه بیشتری (10467 كیلوگرم در هكتار) برخوردار بود. علی‌رغم تأثیری كه مصرف نیتروژن بر عملكرد ذرت داشت، استفاده نامطلوب آن منجر به آلودگی‌های زیست‌محیطی خواهد شد، بنابراین مصرف منطقی كود نیتروژن براساس نیاز گیاه، باعث افزایش كارایی استفاده از منابع، عملكرد قابل قبول و كاهش مخاطرات زیست‌‌محیطی می‌شود.

<strong >Introduction </strong > Dry matter produced by crops is a function of absorbed radiation and radiation use efficiency. Radiation use efficiency is an effective approach to quantify total dry matter accumulation. It is defined as biomass produced by plant for solar radiation absorbed during growing season. Radiation use efficiency is often calculated from the linear regression slope between total dry matter accumulation and cumulative solar radiation absorbed. It is affected by species, weather conditions, crop management, plant development stages, and the production of photosynthesis compounds. Among the factors of agronomic management, nitrogen fertilizer and crop species are the most important aspects that affect the radiation use efficiency. Therefore, by considering the fact that Kermanshah province has favorable condition in terms of more natural resources such as solar radiation, the aims of the present study were evaluation of nitrogen effect on radiation use efficiency, growth indices and yield of some current maize hybrids. <strong >Materials and Methods </strong > A split plot experiment was done based on randomized complete block design with 4 replications at 2014. Treatments were 4 levels of nitrogen fertilizer application (40%, 70%, 100% and 140% of the maize demand to nitrogen which based on the amount recommended by soil experiment equivalent to 138, 238, 350 and 483 kg.ha-1 of urea) as main plots and 3 maize hybrids KSC-704, BC-678 and Simon as sub plots. Leaf area index and total dry matter yield measured during growing season. Crop growth rate and relative growth ratio calculated by differentiation from fitted equation on total dry matter yield data. In order to calculate radiation use efficiency, sunny hours for Kermanshah latitude obtained from the nearest weather station. Daily solar radiation simulated by the method cited by Goudriaan and Van Laar (1993) for growing season. The absorbed radiation in each stage obtained through the multiplication simulated daily solar radiation in percent of absorbed radiation. The amount of cumulative absorbed radiation calculated through the multiplication simulated daily radiation in integral of absorbed photosynthetically active radiation fraction. Finally, radiation use efficiency calculated through the slope of linear regression between dry matter accumulation and cumulative absorbed photosynthetically active radiation. Also, grain yield measured for each treatment separately in the physiological maturity time. <strong >Results and Discussion </strong > The results showed that maximum and minimum of leaf area index, leaf area duration, crop growth rate and total dry matter yield were observed in KSC-704 and BC-678 hybrids, respectively. Also in all 3 hybrids, maximum leaf area index, leaf area duration, radiation absorption, crop growth rate, relative growth ratio and total dry matter yield improved by increasing of nitrogen fertilizer application from 138 to 483 kg.ha-1 of urea. The highest total dry matter yield (20450 kg ha-1) was related to 704 hybrid and consumption of 483 kg ha-1 of urea. Simon hybrid had higher grain yield than other hybrids at 483 kgha-1 of urea condition (10467 kg ha-1). Radiation use efficiency was not significantly different among maize hybrids. Regardless maize hybrids, by increasing of nitrogen fertilizer application from 138 to 238, 350 and 483 kg ha-1 of urea, radiation use efficiency improved from 2.33 to 2.63, 2.81 and 2.84 g MJ-1 (about 13%, 21% and 22%), respectively. Our results also indicated that there was a positive and significant correlation between radiation use efficiency and maximum leaf area index, maximum radiation absorption, maximum crop growth rate, maximum relative growth ratio, and maximum total dry matter. The positive correlation between radiation absorption with crop growth rate (0.98) and total dry matter (0.97) demonstrated more radiation absorbed lead to more crop growth rate subsequently higher total dry matter production by maize hybrids. Nitrogen fertilizer also improved total dry matter yield (58%) and grain yield (63%). <strong >Conclusions </strong > The results indicated that despite effects of nitrogen fertilizer application on maize grain yield, but unfavorable application of nitrogen would be led to intensify environmental pollution. Therefore, consumption of nitrogen fertilizer based on plant demand leads to increase resources use efficiency and reduce environmental risks.