بررسي اثر كم آبياري تنظيم شده و كم آبياري ناقص ريشه بر پارامترهاي فيزيولوژيكي و فتوسنتزي ذرت علوفه اي

An Investigation on Physiological and Photosynthetic Parameters of Forage Maize at Regulated Deficit Irrigation and Partial Root Zone Draying Methods

به منظور بررسی اثر میزان آب آبیاری و روش اعمال كم آبیاری بر عملكرد و پارامترهای فیزیولوژیكی و فتوسنتزی ذرت علوفه ای رقم سینگل كراس 704، آزمایشی در سال زراعی 1393، در مزرعه پژوهشی مركز تحقیقات كشاورزی و منابع طبیعی خراسان رضوی انجام شد. آزمایش به صورت فاكتوریل در قالب بلوك های كامل تصادفی در 4 تكرار اجرا گردید. تیمارهای مورد بررسی عبارت بودند از تیمار آبیاری كامل، كم آبیاری تنظیم شده با تأمین 80 و 60 درصد نیاز آبی، آبیاری ناقص ریشه به طور متغیر (PRD) و تأمین 100، 80 و 60 درصد نیاز آبی و آبیاری ناقص ریشه به طور ثابت (FPRD) و تأمین 100، 80 و 60 درصد نیاز آبی. نتایج آزمایش نشان داد كه همزمان با كاهش میزان آب مصرفی عملكرد تر و خشك علوفه ذرت در تیمار كم آبیاری تنظیم شده كاهش یافت اما در تیمار آبیاری ناقص ریشه به طور متغیر تفاوت معنی داری بین میزان عملكرد در تیمارهای تامین 100 و 80 درصد نیاز آبی مشاهده نشد. بیشترین عملكرد علوفه تر با میانگین 72099 كیلوگرم در هكتار مربوط به تیمار آبیاری كامل بود. بررسی صفات فیزیولوژیك طی چهار مرحله نمونه برداری در طول فصل رشد، نشان داد كه شاخص سطح برگ تحت اثر متقابل تیمارهای آبیاری قرار گرفت. تفاوت معنی داری بین شاخص سطح برگ گیاهان در تیمار آبیاری كامل و سطوح 100 و 80 درصد تامین آبی در تیمار PRD وجود نداشت. همبستگی مثبت و معنی داری بین شاخص سطح برگ و عملكرد علوفه تر (r2= 0.98, p <0.01) مشاهده شد. نتایج نشان داد كه محتوای آب نسبی برگ پرچم و شاخص كلروفیل و هدایت روزنه ای با كاهش میزان آب مصرفی كاهش یافت. كاربرد روش PRD در مقایسه با اعمال كم آبیاری به روش تنظیم شده روند اثرات منفی خشكی را كاهش داد.

Introduction: Water shortage is the most important factor affecting crop production in the world. The deficit irrigation is a way to reduce water consumption in farming. The Partial Root- zone Drying (PRD) irrigation is a new improvement in deficit irrigation in which the half of the root zone is irrigated alternatively in scheduled irrigation events. In the fixed partial root zone drying (FPRD) the irrigation is fixed to one side of the root zone in the growing season. Maize is a drought sensitive crop. In maize, secondary traits related to drought resistance are considered in producing tolerate cultivars. Materials and Methods: An experiment was conducted in order to investigate the effects of regulated deficit irrigation, variable partial root zone drying (PRD) and fixed partial root zone drying (FPRD) on the yield, physiological and photosynthetic parameters of forage maize (KSC 704) during the growing seasons of 2014 in Mashhad region. A factorial experiment based on randomized complete block design with four replications was carried out. The treatments included the full irrigation (FI) and the deficit irrigations (regulated deficit irrigation (DI) and the replacements of 80 % (DI80) and 60 % (DI60) of total water requirement, fixed PRD (FPRD) at 100% (FPRD100), 80% (FPRD80) and 60%(FPRD60) of water requirement, and variable PRD at 100% (PRD100), 80% (PRD80) and 60% (PRD60) of water requirement). Drip irrigation tapes were placed between plant rows. In the full irrigation and regulated deficit irrigation treatments, the plants were irrigated from two sides for every irrigation. In the PRD, one of two neighboring tapes was alternatively used for irrigation. In FPRD, a drip tape was used for two plant rows and irrigation was fixed to one side of the root. The irrigation interval was 3 days for all treatments. Dry and fresh forage yield, leaf area index (LAI), stomatal conductance, leaf relative water content (RWC) and chlorophyll content were measured. Results and Discussions: All the measured traits were affected by the deficit irrigation. The highest fresh forage yield (72099 kg/ha) was produced by the full irrigation treatment. The statistical comparison showed that there was no significant difference between regulated deficit irrigation and PRD method for the fresh forage yield. But the FPRD treatment reduced the fresh forage yield. There was no significant difference between the fresh forage yield of FI and PRD80 treatments. The dry forage yield was affected by the different irrigation methods, irrigation levels and the interaction effects of the treatments (p <0.01). The highest dry forage yield (17590 kg/ha) was produced by the full irrigation treatment. There was no significant difference between dry forage yield of FI, PRD100 and PRD80 treatments. The lowest dry forage yield with an average of 10229 kg per hectare belonged to FPRD60 treatment. In a review study the positive effects of PRD have been reported by Sepaskhah and Ahmadi. The highest water use efficiency by an average of 2.36 kilograms of dry matter per one cubic meter of water consumption (kg/m3) belonged to PRD80 treatment. During growing season, reduction the amount of irrigation water in all the methods of irrigation reduced the leaf area. The greatest reduction in the leaf area due to water stress was observed at the end of the growing season. The LAI was affected by interaction between irrigation level and water deficit method. However, there was no significant difference between FI, PRD100 and PRD80 treatments. The fresh forage yield (r2= 0.98, p <0.01) significantly correlated with the LAI. The results showed that the RWC, chlorophyll content and stomatal conductivity were reduced by water deficit. There was no significant difference between the RWC of the FI, PRD100 and PRD80 treatments. Also, no significant difference between the RWC of the DI and PRD methods was observed but the FPRD method decreased the RWC. Correlation analysis showed a significant correlation between the RWC and the fresh forage yield. At the end of the growing season, the chlorophyll content decreased in all the treatments due to the aging of the leaves. The most decrease belonged to the DI60 and FPRD60 treatments. Among the different methods of irrigation, the maximum chlorophyll content by 56% belonged to the PRD method. Significant correlation between chlorophyll content, LAI and RWC was observed. During the growing season, reduction the amount of irrigation water reduced the stomatal conductance. No significant difference between the stomatal conductance of the DI and PRD methods was observed. The minimum stomatal conductance belonged to the FPRD treatment. A significant correlation was observed between the stomatal conductance and RWC. The reduction of the leaf area under drought stress reduced the plant photosynthesis and thus reduced the plant biological yield. The drought stress through stomatal closure and the lack of carbon dioxide in the chloroplasts of plant affects plant photosynthesis and reduces dry matter production. In the partial root zone drying irrigation method, water stress in the dry portion of root zone causes the stomatal closure, abscisic acid production and plant respiration reduction. On the other hand, water uptake in the wet portion of root zone causes plant water conservation and plant growth continuation which improves irrigation water productivity. Conclusion: According to the results, it seems that the negative effects of water stress on physiological and photosynthetic parameters in the early growing season is not significant and increases with the aging of the plants. Water stress decreases the absorption of carbon dioxide and the photosynthesis by reduction in the stomatal conductance. As well as, reducing the leaf area decreased photosynthetic area and the production of asymylats in the water stress conditions and ultimately reduced the forage yield significantly. The PRD method increased irrigation water productivity. With respect to this fact that no difference between the dry matter yield, LAI, chlorophyll content and RWC in the FI, PRD100 and PRD80 treatments was observed, it seems that applying Partial Root- zone Drying (PRD) method will result in lower water consumption during forage maize production at Mashhad environmental conditions.