تاثیر خاک‌ورزی، تنش کمبود آب و کود نیتروژن بر عملکرد ذرت علوفه‌ای (.zea mays l)

به‌منظور بررسی تاثیر تیمار کود نیتروژن و تنش کمبود آب بر عملکرد ذرت علوفه‌ای در شیوه‌های مختلف خاک‌ورزی، آزمایشی در مزرعۀ آموزشی و پژوهشی دانشگاه تهران در سال‌های 1397 و 1398 انجام شد. این آزمایش به صورت کرت‌های دو بار خردشده در قالب طرح بلوک‌های کامل تصادفی در سه تکرار اجرا شد. خاک‌ورزی به عنوان عامل اصلی در دو سطح (بدون‌خاک‌ورزی و مرسوم)، تنش کمبود آب به عنوان عامل فرعی (در سه سطح تامین 30، 60 و 90 % نیاز آبی) و کود نیتروژن به عنوان عامل فرعی‌فرعی (در سه سطح مصرف صفر، 50 و 100 % میزان توصیه‌شده) در نظر گرفته شدند. نتایج جدول تجزیه واریانس نشان داد بالاترین قطر ساقه ( 19.8 میلی‌متر) از اثر متقابل تنش کمبود آب خفیف و خاک‌ورزی مرسوم حاصل شد. بالاترین شاخص سطح برگ (6.08)، وزن خشک برگ (441.58 گرم بر متر مربع)، وزن خشک ساقه (1478.2 گرم بر متر مربع)، وزن خشک کل بوته (1919.93 گرم بر متر مربع) و وزن تر کل بوته (6732.6 گرم بر متر مربع) از تنش کمبود آب خفیف، کاربرد 100% کود نیتروژن توصیه شده در شرایط خاک‌ورزی مرسوم حاصل شد. همچنین بیشترین کارایی مصرف نیتروژن (428/68 کیلوگرم بر کیلوگرم) از اثر متقابل خاک ورزی مرسوم با مصرف 50% کود نیتروژن موردنیاز گیاه در شرایط تنش کمبود آب خفیف حاصل شد. ازآنجاکه وزن تر بوته در روش بدون خاک ورزی تفاوت معنی داری با روش خاک ورزی مرسوم نداشت ولی کارایی مصرف آب بالاتری (5/8%) را نشان داد، به منظور کاهش مصرف آب روش بدون خاک ورزی نسبت به خاک ورزی مرسوم پیشنهاد می گردد.

Effect of tillage, irrigation and nitrogen fertilizer on crop yield of forage maize (Zea mays L.)

Introduction Corn (Zea mays L.) for its high potential in the production of yield is critical. Given Iran’s position in the arid and semiarid belt of the world, the issue of drought, salinity, and their effects on crops should be considered more than any other nonbiological stress. Drought stress is a global problem that threatens the growth of crops and food security (Jaleel et al., 2009). Drought stress affects biomass and eventually, yield losses by affecting physiological processes, growth and development of plant tissues (Orfanou et al., 2019). Irrigation and nitrogen mismanagement have been considered as the most critical factors in reducing maize yield (Norwood, 2000). Although nitrogen is critical for the growth of plants, the negative growth response to the excess of nitrogen fertilizer under drought stress (Cabrera, 2004) must be considered. Conservation tillage due to improved water, carbon and nitrogen resources in the soil has the remarkable ability to optimize crop production in arid and semiarid regions of the world (Husnjak et al., 2002). Optimal leaf aria deployment is crucial for photosynthesis performance and dry matter production (Aslam et al., 2013). Decrease in leaf area index following drought stress (Karam, 2005) and a decrease in plant height and grain weight following reduction of nitrogen levels and increase in drought intensity (Kalamian et al., 2006) have been reported previously. It has been suggested that no3tillage under drought stress and conventional tillage under normal water demand, will cause increased yield (Ruisi et al., 2014). The results of different researches on the application of tillage methods on maize crop varied, with no significant differences in plant traits (height, leaf area index and dry weight) as a result of longterm application of different tillage methods (Ram et al. 2010), no significant effect of tillage on plant growth and yield (Jat et al., 2006) and improved growth and yield enhancement in nontillage under compacted soils due to improved aeration And increased seedling emergence (Morrison et al., 1990). This study was conducted to study the effects of different tillage methods, different nitrogen fertilizer levels and drought stress on forage maize yield.   Materials and methods This study was carried out to study the effect of irrigation and nitrogen fertilizer on crop yield of forage maize cultivated under conventional and conservation tillage systems, an experiment was conducted in 2018 and 2019 in split split plots on randomized complete block design with three replications in farm of University of Tehran. Tillage systems as the main plot in two factors was including conversation and conventional tillage, Water stress as the subplot in three levels by 30, 60 and 90 Percent of moisture requirement and nitrogen urea as the subsub plot at three levels by 0, 50 and 100 Percent of the recommended rate.   Results The combined variance analyses indicated that the highest stem diameter (19.8 mm) was obtained from the interaction of water slightly stress and conventional tillage. the highest leaf aria index (6.08), leaf dry weight (441.58 g m2), stem dry weight (1478.2 g m2), total dry weight (1919.93 2) and total fresh weight (6732.6 2) was obtained from the interaction of conventional tillage, 90 and 100 percent water and nitrogen demand, respectively. The effect of drought stress on stem diameter reduction in conservation tillage compared to conventional tillage can be due to decreased root penetration and consequently reduced nutrient uptake by the plant. Decrease of leaf area index due to drought stress (UrRahman et al., 2004) and increase of leaf area index with increased irrigation levels and supply of required amounts of nitrogen fertilizer (Lack et al., 2008), previously has been reported. Loss of leaf dry weight following water stress can be attributed to decreased water uptake and, most likely disruption of plant photosynthetic processes and sap production.   Conclusions According to the results of two years of study, it is concluded that the interaction between drought stress and nitrogen fertilizer in conventional tillage with severe drought stress will decrease yield. Nitrogen fertilizer management is critical under these conditions.