اثر تراکم کاشت بر میزان جذب و کارایی مصرف تشعشع ژنوتیپ‌های برنج (oryza sativa l.) در شرایط کشت مستقیم

به‌منظور بررسی میزان جذب و کارایی مصرف نور و همچنین تعیین ضریب استهلاک نوری در سه ژنوتیپ برنج در تراکم‌های مختلف کشت مستقیم، آزمایشی به‌صورت فاکتوریل در قالب طرح پایه بلوک‌های کامل تصادفی با سه تکرار و 15 تیمار در مزرعه تحقیقاتی موسسه تحقیقات برنج کشور رشت اجرا شد. تیمارهای مورد مطالعه شامل پنج تراکم بذر (65، 80، 95، 110 و 125 کیلوگرم بذر در هکتار) و سه ژنوتیپ برنج (لاین امید بخش طاهر، رقم آنام و رقم هاشمی) بودند. نتایج نشان دادکه بیشترین عملکرد دانه در رقم طاهر (6380 کیلوگرم در هکتار) و رقم آنام (6100 کیلوگرم در هکتار) در تراکم 95 کیلوگرم بذر در هکتار به‌دست آمد ولی بیشترین عملکرد دانه در رقم هاشمی (5490 کیلوگرم در هکتار) در تراکم 110 کیلوگرم بذر در هکتار مشاهده شد. در این تحقیق، بیشترین (3.06 گرم بر مگاژول par) و کمترین (2.20 گرم بر مگاژول par) میزان کارایی مصرف نور به‌ترتیب در تراکم‌های 95 و 125 کیلوگرم لاین طاهر مشاهده شد. دو ژنوتیپ آنام و طاهر در تراکم 95 کیلوگرم در هکتار به‌ترتیب با 773 و 852 مگاژول par بر متر مربع و رقم هاشمی در تراکم 110 کیلوگرم در هکتار با 880 مگاژول par بر متر مربع، بالاترین میزان جذب تشعشع در طول فصل رشد را داشتند. افزایش تراکم تا سطح مطلوب در ارقام برنج باعث افزایش جذب و همچنین کارایی مصرف نور گردید. بین جذب و کارایی نور با عملکرد زیستی و دانه ارقام برنج همبستگی مثبتی مشاهده شد.

Effect of Seeding Density on Radiation Absorption and Use Efficiency of Rice (Oryza sativa L.) Genotypes under Direct Seeding Conditions

Introduction: Effective use of sunlight is a great opportunity to improve crop productivity. In conditions without growth limiting factors, there is a linear relationship between radiation absorption and dry matter production in plants, that the slope of this relationship is radiation use efficiency. In addition to genotyping, radiation use efficiency is affected by crop management. Changes in density of rice varieties by affecting leaf area index and light extinction coefficient change the amount of absorption and distribution of light within the canopy and thus affect dry matter production. Therefore, the response of different rice cultivars to change in density is not same. According to this, the present study was carried out to investigate the radiation absorption and efficiency of use and also determine the light extinction coefficient in new and old rice cultivars at different direct seeding densities in Rasht climatic conditions.Material and Methods: The present experiment was carried out as a factorial based on randomized complete block design with three replications at research field of Rice Research Institute of IranRasht. Treatments included five levels of densities (65, 80, 95, 110, and 125 kg ha1) and three levels of cultivar (Taher (promising line), Anam and Hashemi). Sampling was performed once every two weeks, 25 days after emergence. Sampling was performed with 0.5×0.5 m quadrates to measure leaf area, dry weight, and radiation in different treatments.Results and Discussion: The results showed that the interaction effect of cultivar and density on radiation use efficiency, LAI, grain and biological yield were significant. Harvest index was affected only by density and light extinction coefficient was not affected by any density and cultivar treatments. The highest grain yield of Taher (6380 kg ha1) and Anam cultivars (6100 kg ha1) were obtained in 95 kg ha1 density, while the highest yield of Hashemi cultivar (5490 kg.ha1) was observed in 110 kg ha1 density. Grain yield followed biological yield, and treatments with higher biological yield had higher grain yield. The highest leaf area index (5.63) was observed in Hashemi cultivar and 110 kg ha1 density in 70 days after emergence. At this stage, the lowest leaf area index (4.21) was observed in Taher cultivar at 65 kg ha1 density. Although, in the early stages of growth, higher densities had a higher rate of leaf area expansion, but the highest leaf area index did not differ significantly between 95, 110, and 125 kg ha1 densities. The light extinction coefficient of this experiment varied from 0.4 to 0.5 in different cultivars and densities and Taher cultivar had the higher light extinction coefficient. Although, no significant difference was observed between treatments. The highest grain yield of Taher (6380 kg ha1) and Anam (6100 kg ha1) cultivars were obtained in 95 kg ha1 density, but the highest yield of Hashemi (5490 kg ha1) was obtained in 110 kg ha1. In this study, the highest (3.06 g MJ1 PAR) and the lowest (2.20 g MJ1 PAR) radiation use efficiency were observed at 95 and 125 kg ha1 of Taher cultivar, respectively. In all cultivars, the lowest radiation use efficiency was observed at density of 125 kg ha1. Anam and Taher cultivars had the highest radiation absorption (773 and 852 MJ1 PAR, respectively) during the growing season at 95 kg ha1. Although, the highest radiation absorption of Hashemi (880 MJ1 PAR) cultivar was obtained at 110 kg ha1 density.Conclusions: The results showed that Taher cultivar had the highest grain and biological yield compared to Anam and Hashemi cultivars. Based on yield, the best density was 95 kg ha1 for Anam and Taher cultivars and 110 kg ha1 for Hashemi cultivar. Increasing the density of rice cultivars to the optimum level increased the radiation absorption and use efficiency. There was a positive correlation between radiation absorption and efficiency with biological and grain yield of rice cultivars.