بهینه‌سازی آبیاری و تراکم کاشت ذرت (.Zea Mays L) به‌کمک روش سطح-پاسخ

با افزایش کارایی مصرف آب از طریق عملیات مدیریتی نظیر تراکم مناسب کاشت و میزان آبیاری می توان در مناطق خشک و نیمه‌خشک عملکرد محصول را افزایش داد. به همین منظور آزمایشی در سال زراعی 1394 به‌روش سطح-پاسخ (rsm) در قالب طرح مرکب مرکزی با دو تکرار روی گیاه ذرت (.zea mays l) در مزرعه تحقیقاتی دانشکده کشاورزی دانشگاه فردوسی مشهد انجام شد. تیمارهای آزمایش با توجه به سطوح بالا و پایین حجم آبیاری (6000 و 14000 مترمکعب در هکتار) و تراکم کاشت (پنج و نه بوته در مترمربع) طراحی شدند. عملکرد دانه، عملکرد بیولوژیک و کارایی مصرف آب به‌عنوان متغیرهای وابسته مورد ارزیابی قرار گرفتند و با استفاده از مدل رگرسیونی درجه دو کامل واکنش این صفات به متغیرهای مستقل (تراکم و آبیاری) محاسبه شدند. سپس مقدار مصرف آب و تراکم ذرت بر اساس سه سناریوی اقتصادی، زیست‌محیطی و اقتصادی-زیست‌محیطی بهینه سازی شدند. در سناریوی اقتصادی با در نظر گرفتن هشت بوته در مترمربع و آبیاری 14000 مترمکعب در هکتار بیشترین میزان عملکرد اقتصادی با 1345.8 گرم در مترمربع به‌دست آمد که در این شرایط عملکرد بیولوژیک و کارایی مصرف آب به‌ترتیب 4534.7 گرم در مترمربع و 0.98 کیلوگرم به‌ازای هر مترمکعب آب بود. در سناریوی زیست‌محیطی نیز از انتخاب تراکم هفت بوته در مترمربع و آبیاری 7939 مترمکعب در هکتار بیشترین میزان کارایی مصرف آب (kg.m3 1.21) حاصل شد که تحت این شرایط عملکرد دانه 988.6 گرم در مترمربع بود. بر اساس سناریوی اقتصادیزیست محیطی، با انتخاب تراکم 7.5 بوته در مترمربع و آبیاری معادل 10848 مترمکعب در هکتار، بیشترین میزان عملکرد دانه و کارایی مصرف آب به‌ترتیب با 1240.7 گرم در مترمربع و 1.16 کیلوگرم به‌ازای هر مترمکعب آب به‌دست آمد. بنابراین، به‌طورکلی مصرف آب و انتخاب تراکم بر اساس سناریوی تلفیقی به‌دلیل در نظر گرفتن توام مسائل اقتصادی و زیست‌محیطی نسبت به سناریوهای دیگر برتری دارد.

Optimization of Irrigation and Plant Density of Corn (Zea mays L.) by Using Response-Surface Methodology

Introduction[1]   Water and plant density have a complex interaction. Determination of optimum density is an effective strategy to improve the efficiency of available resources usage and to increase the yield per unit area. Despite extensive research on the effects of different levels of irrigation and plant density for different crops, including corn, information on the optimization of these resources, using responsesurface methodology (RSM) is scarce. Therefore, the objective of this study was to determine the optimal level of irrigation and plant density in corn production based on central composite design (CCD). Materials and Methods  An experiment was conducted by using responsesurface methodology with the central composite design and two replications on corn at the Research Farm of Ferdowsi University of Mashhad, during the 2015 growing season. The experimental treatments were the highest and lowest levels of irrigation volume (6000 and 14000 m3.ha1) and plant density (5 and 9 plants.m2). Grain yield (GY), biological yield (BY) and water use efficiency (WUE) were measured as response variables in a full quadratic polynomial model. Consumption rate of irrigation and density were optimized based on three scenarios: economic, environmental and ecoenvironmental. Grain yield of corn and WUE were considered as the main factors to determine the optimum level of treatments under the economical and environmental scenarios, respectively. In the ecoenvironmental scenario, the main factor was WUE and grain yield. Results and Discussion The results indicated that at low level of irrigation (6000 m3.ha1) plant density and grain yield correlated with others as quadratic so that by increasing the density from 5 to 7 plants.m2,grain yield first increased and then decreased with enhancing density to 9 plants.m2.It seems that at low levels of irrigation, reduction and enhancement of plant density, respectively, as a result of increasing evaporation from soil surface and increasing competition in resource uptake (light and water) has reduced grain yield. Grain yield at high levels of irrigation showed a relatively linear relationship with incrementing plant density, and the highest grain yield with 1324.9 g.m2was obtained from treatment of 14000 m3.ha1 of water and density of 9 plants.m2. Nevertheless, the results of model fitting showed that the highest grain yield with 1318.4 g.m2 was attained from the density of 7 plants.m2 and 14000 m3.ha1 of water. Therefore, it seems that with the simultaneous enhancement in plant density and irrigation, vegetative growth due to lack of light has increased, as a result of grain yield than optimum densities (7 plants.m2) has shown a decrease. The regression model could significantly indicate that impact of independent variables on the grain yield, biological yield and water use efficiency (dependent variable). In economic scenario with considering 8 plants.m2 and irrigation of 14000 m3.ha1 the maximum of economical yield with 1345.8 g.m2 was achieved in which biological yield and water use efficiency were 4534.7 gr.m2 and 0.98 kg.m3 of water, respectively. In environmental scenario also the choice of the density of 7 plants.m2 and irrigation of 7939 m3.ha1 the highest water use efficiency (1.21 kg.m3) was attained in which grain yield that was 988.6 g.m2. Based on ecoenvironmental scenario with choice of the density of 7.5 plants.m2 and irrigation of 10848.5 m3.ha1 the maximum grain yield and water use efficiency was obtained in 1240.7 g.m2 and 1.16 kg.m3 of water, respectively. Conclusion Due to lack of water resources and environmental problems caused by the excessive use of water, applying appropriate management practices such as proper planting density to optimize these resources is essential. The best way to achieve the highest economic yield and water use efficiency and, to reach sustainable agriculture is the choice of ecoenvironmental scenario in which by application of the density of 7.5 plants.m2 and irrigation level of 10848.5 m3.ha1 the maximum grain yield and water use efficiency with 1240.7 g.m2 and 1.16 kg.m3 of water was obtained, respectively.