بررسی تاثیر تنش کم‌آبی و مقادیر مختلف کود نیتروژن بر عملکرد، اجزای عملکرد و کارآیی مصرف آب سیب‌زمینی (Solanum Tuberosum L.)

به‌منظور بررسی اثر سطوح مختلف تنش کم‌آبی و کود نیتروژن بر عملکرد و سایر صفات زراعی سیب‌زمینی رقم بورن، آزمایشی در سال زراعی 92-1391 با سه سطح تنش کم‌آبی s1، s2 و s3 (به ترتیب تامین 100، 75 و 50 درصد نیاز آبی سیب‌زمینی پس از سبز شدن تا پایان دوره رشد) به‌عنوان فاکتورهای اصلی و 4 تیمار کود نیتروژن n1، n2، n3 و n4 (به ترتیب تامین 100، 66، 33 و صفر درصد نیاز کودی) به‌عنوان فاکتورهای فرعی به‌صورت کرت‌های خردشده، در قالب طرح بلوک‌های کامل تصادفی با سه تکرار در مرکز تحقیقات کشاورزی و منابع طبیعی استان چهارمحال و بختیاری به اجرا درآمد. در این آزمایش، تنش کم‌آبی درصد ماده خشک غده‌ها را افزایش داد، اما مقادیر نیتروژن روند مشخصی در تغییرات این صفت ایجاد نکرد. با اعمال تنش خشکی و کاهش مصرف کود نیتروژن تعداد غده در بوته و وزن غده‌ها کاهش یافت. عملکرد غده قابل‌فروش در تیمار‌های s1 و s2 اختلاف معنی‌دار نداشت اما تنش آبی (s3) منجر به افت شدید عملکرد شد. تیمارهای n1، n2 و n3 باعث افزایش عملکرد غده قابل‌فروش به ترتیب به میزان 30، 36 و 11 درصد نسبت به شاهد (n4) شدند. به علت کاهش عملکرد غده در تیمارهای s2 و s3 در بالاترین سطح مصرف نیتروژن (n1)، اثر متقابل تنش خشکی و نیتروژن بر عملکرد غده، معنی‌دار شد. تیمار n2 در شرایط تنش شدید کم‌آبی و تنش متوسط دارای بالاترین و تیمار n4 در شرایط بدون تنش دارای کمترین کارآیی مصرف آب بود. بر اساس تجزیه رگرسیون مرحله‌ای، صفت میانگین وزن غده قابل‌فروش به‌تنهایی بیشتر تغییرات عملکرد غده در واحد سطح را توجیه کرد.

Effects of water deficit and different nitrogen fertilizer levels on yield, yield components and water use efficiency of potato (Solanum tuberosum L.)

Introduction Potato (Solanum tuberosum L.) is one of the most important crops that plays a major role in feeding the world. The growing demand for potato, as both a fresh and processed food, along with the increase in world population, mean that yield will have to be improved through some combination of germplasm enhancement, better crop protection and more efficient and productive management of irrigation and fertilization (Haase et al., 2007). Researches have proved potato is sensitive to drought stress at all stages of growth, especially at tuber formation stage due to reduction of leaf area and photosynthesis (Fabeiro et al., 2001 Ayas, 2013 Shock et al., 2013). Abiotic stress factors, such as drought, have severe, adverse effects on potato growth and yield. In particular, a regular water supply is necessary to achieve a high quality yield (Ierna and Mauromicale, 2006). In comparison with other species, potato is very sensitive to water stress because of its shallow root system (Ayas, 2013). Water shortage during tuber differentiation can delay growth and reduce earliness, whereas during tuber growth and bulking can decrease tuber size and have a drastic effect on yield (Alva et al., 2012 Liu et al. 2006 Ayas, 2013). For processing potato, a careful N and water management is required to ensure regular growth, high dry matter content and marketable tubers (Shock et al., 1998 Zhang et al., 2006 Shahnazari et al., 2007). So this research was done to evaluate effects of different levels of water deficit and nitrogen fertilizer on tuber yield, yield components and water use efficiency of potato crop in Chahar Mahal va Bakhtiari province, in Iran. Materials and methods In order to study the effects of different levels of water deficit and nitrogen fertilizer on tuber yield and other agronomic traits of potato crop (Boren variety), a split plot experiment based on randomized complete block design, conducted at Chahar Mahal va Bakhtiari Research Center of Agriculture and Natural Resources, in 2013. The levels of water deficit were S1, S2 and S3 (100, 75 and 50% of the water requirement of potato crop after emergence by the end of the growing season, respectively), as the main plots and nitrogen fertilizer treatments were N1, N2, N3 and N4 (100, 66, 33 percent of plant nitrogen requirement and without nitrogen consumption, respectively) as sub plots. Results and discussion In this experiment water deficit had decreasing effect on tubers dry matter percent but nitrogen changes had no distinct effect on this trait. By applying water deficit and decreased levels of nitrogen, the number of tubers per plant and the average tubers weight also fell. The greatest and the lowest number of tubers per plant were seen at S1 and S3 treatments (8.4 and 7.4 respectively). The maximum weight of tubers observed at full irrigation treatment (118 g) that had no significant difference with S2, but at treatment S3 (50% of the water requirement), tubers were produced lighter with an average weight of 86.6 grams. So it can be concluded, in this irrigation regime, the average weight of tubers is closer to weight of seed tuber class. Many studies have confirmed these findings (Fabeiro et al., 2001 Ayas and Korukcu, 2010 Ayas, 2013). The results showed that maximum tuber yield gained from S1 treatment (55.9 ton/ha) that had no significant difference with S2, but intensive drought stress (S3) produced minimum tuber yield (31.7 ton/ha). N1 and N2 treatments led to highest tuber yield but the lack of nitrogen (N4) caused the lowest tuber yield (38.7 ton/ha). Generally, in S2 and S3 drought stress levels, N2 produced maximum tuber yield. The reduction of tuber yield in S2 and S3 treatments within increment of nitrogen consumption (N1), caused the significant interaction between drought stress and nitrogen on tuber yield. Ierna and Mauromicale (2006) reported that water deficit stress as much as 50% of the water requirement, had increased stomatal resistance and caused the reduction of leaves photosynthesis, biomass, tuber growth and tuber yield. Demelash, 2013 Alva et al., 2012 and Ayas, 2013 studies also confirm the results of this Research. The second level of nitrogen (N2) in S3 treatments led to maximum, but S1N4 led to minimum water use efficiency (9.21 and 5.24 kg/m3 respectively). Liu et al. (2006) reported, by reducing the amount of irrigation volume, tuber yield decreases baut water use efficiency will increase.The stepwise regression analysis showed that the average tuber weight explains most changes of marketable tuber yield per plot. Conclusions Based on the results of the present study, since there is no statistical difference in tuber yield, between S1 and S2 irrigation regimes, it is recommended that for proper utilization of water resources and achieve economic yield, potato crop, produce with 6400 m3 water per hectare with irrigation at 7 days period. Results showed, at S2 irrigation regime, N2 Treatment (consumption of 270 kg Urea/ ha) had produced the highest yield, so S2N2 treatments is the best option for potato crop production.