تاثیر تاریخ کاشت و رژیم های مختلف آبیاری بر عملکرد و راندمان مصرف آب در ذرت دانه ای

به منظور تعیین تاریخ کاشت مناسب تر و مدیریت آب آبیاری در دوره رشد ذرت دانه ای (s.c.704) آزمایشی در قالب کرت های خرد شده بر پایه طرح بلوک های کامل تصادفی با سه تکرار در دو سال زراعی 95-1394 در مزرعه تحقیقاتی دانشکده کشاورزی دانشگاه تهران انجام شد. عوامل آزمایشی شامل سه تاریخ کاشت: یکم اردیبهشت، بیست و یکم اردیبهشت و دهم خرداد در کرت های اصلی و چهار سطح آبیاری (i40:40%etc, i60:60%etc, i80:80%etc and i100:100%etc) براساس نیاز آبی گیاه در کرت های فرعی اجرا شد. نتایج نشان دهنده کاهش عملکرد دانه به میزان 44 و 49 درصد به ترتیب در سال اول و دوم آزمایش در تیمار تنش کم آبیاری بر اساس 40 درصد نیاز آبی در مقایسه با تیمار شاهد آبیاری بر اساس 100 درصد نیاز آبی گیاه بود. عملکرد دانه در سال دوم به طور معنی داری (0.01 ≤p) به اثر متقابل بین تاریخ کاشت و آبیاری واکنش نشان داد به نحوی که سطوح بالای تبخیر و تعرق و تنش حرارتی شدید با اثر منفی بر مرحله گرده افشانی ذرت از عوامل اصلی تاثیرگذار در کاهش عملکرد دانه در تاریخ کاشت بیست و یکم اردیبهشت و دهم خرداد بودند. بالاترین مقادیر راندمان مصرف آب عملکرد دانه و زیست توده در تیمار کم آبیاری (i40) مشاهده شدند. ذرت های کاشته شده در تاریخ کاشت یکم اردیبهشت با افزایش طول دوره رشد و شرایط دمایی مناسب برای پرشدن دانه از توانایی بیشتری در تولید دانه های با وزن بالا برخوردار بودند. با توجه به شرایط اقلیمی منطقه، اتلاف آب از طریق تبخیر سطحی در ابتدای فصل رشد به مراتب کمتر می باشد. بنابراین انتخاب تاریخ کاشت زودهنگام ذرت دانه ای و پرهیز از آبیاری های مازاد بر نیاز گیاه برای دست یابی به حداکثر عملکرد بهینه و بهبود راندمان مصرف آب حائز اهمیت می باشند.

The effect of planting date and different irrigation levels on yield and irrigation efficiency in grain maize

IntroductionIn many parts of the world where agriculture is important, crops usually encounter a large variation in water supply during their growing seasons. Thus, water deficit is a major constraint to crop production, even in humid environments (Soltani and Sinclair, 2012). In the context of improving water use efficiency (WUE), there is growing interest in deficit irrigation which involves applying stress levels to plants that have minimal effects on yields in order to optimize yields per unit of water used as well as crop returns increment (Rodrigues and Pereira 2009). One of the planting date goals is to detect the time after which crops could be able to keep immune even versus adverse climatic conditions Berzsenyi & Lap (2005). Arid and Semiarid climate in the most parts of Iran with limited water resources highlights applying adaptive methods as well as new approaches to support crop producers in selecting proper varieties, accurate planting date and using water in an optimum way to maximize productivity and‌ returns.‌Material and methodsIn order to probe those of agronomic traits contributing to final yield and detecting susceptible growth stages of corn to water stress a field study took place in research farm of College of Agriculture and Natural Resources, University of Tehran. Considering irrigation management and planting date as adaptive techniques and due to the rating of relative maturity (RM) of maize hybrids, (S.C. 704) selected as latematuring hybrid in this experiment. The experiment implemented in splitplot template based on randomized complete block design with three replicates in 2015 and 2016 cropping seasons. The experimental treatments consist of three planting dates, (PD1: 21st April, PD2: 11th May and PD3: 31st May) assigned to main plots and four irrigation treatments, (100%ETc, 80%ETc, 60%ETc and 40%ETc) of the estimated evapotranspiration (ET) placed in sub plots.Results and discussionThe lower of grain yield (4150.30 and 3589.60 kg ha1) and less total biomass (14354.60 and 13563.90 kg ha1) resulted in stress treatment of 40%ETc respectively in 2015 and 2016. The highest values of irrigation water use efficiency based either on grain yield (1.39 and 1.20) or total biomass (4.79 and 4.53) were culminated in 40%ETc treatment for the period of two years respectively. It seems that in the presence of deficit irrigation plant capability in converting per unit of water to biomass will be improved through transpiration. Our results corroborated by those of Chaichi et al. (2015) who issued stepwise reduction for ear yield, total dry matter and grain yield in stress treatment as ETc decreased. Also lower rates of harvest index (28.76 and 26.34%) also recorded at 40%ETc treatment in both years respectively. Similar results revealed by Farré and Faci (2006) who found that HI decreased markedly with increasing water stress. The lower values of grain yield and total biomass obtained at the laterplanted corns due to coincidence of pollination phase with the higher levels of temperature and evapotranspiration in mid and late planting dates (PD2 and PD3). ConclusionIn fact crops planted earlier in the season tend to develop more gradually, under cooler temperatures with enough accessibility to more abundant soil water supplies and nitrogen availability. In this experiment, water stress during pollination time affected corns under common planting date (PD2). However, as the tailend maturation of laterplanted corns (PD3) approach cooler temperatures of early autumn, due to rapid loss of leaves there is less time for them to compensate yield losses and generally results in lower overall productivity. To help farmers for applying water more efficiently, they must pay attention to align planting date and applied hybrid with local agroecological endowments to avoid of irrigations that are surplus to requirements.