بررسي اثرات تاريخ كاشت بر شاخص هاي رشد و عملكرد و اجزاي عملكرد ارقام گندم بهاره در نيشابور

Investigating the effects of sowing date on growth indices and yield and yield components of spring wheat cultivars in Neyshabur

به منظور مطالعه بررسي اثرات تاريخ كاشت بر شاخص هاي رشد و عملكرد و اجزاي عملكرد برخي ارقام گندم بهاره آزمايشي در سال 94-1393 در ايستگاه تحقيقات كشاورزي و منابع طبيعي نيشابور انجام شد. در اين راستا شش رقم گندم چمران، پيشتاز، بهار، سيروان، سيوند و پارسي در سه تاريخ كاشت20 مهر،20 آبان و 20 آذر در قالب طرح بلوك‌هاي كامل تصادفي و به صورت كرت هاي خردشده در سه تكرار كشت شدند. تاريخ هاي كاشت در كرت هاي اصلي و ارقام گندم دركرت هاي فرعي قرار گرفتند. نتايج نشان داد با تاخير در كاشت شاخص هاي فيزيولوژيك همچون شاخص سطح برگ، سرعت رشد محصول، وزن خشك تجمعي كاهش يافته است. اثر تاريخ كاشت در سطح 1 درصد بر عملكرد دانه معني‌دار بود، و تأخير در كاشت باعث كاهش عملكرد دانه گرديد. تاريخ كاشت 20 مهر و20 آذر با ميانگين 6113 و 4124 كيلوگرم در هكتاربه ترتيب بيشترين و كمترين عملكرد دانه را داشت . نتايج تجزيه همبستگي نشان داد كه تعداد سنبله در واحد سطح بيشترين تأثير را در بين اجزاء عملكرد بر عملكرد نهايي گندم داشت. همچنين بين عملكرد دانه با متوسط سرعت رشد محصول همبستگي مثبت و معني داري مشاهده شد. نتيجه كلي نشان داد كه تاريخ كاشت 20 مهر با مقدار 6113 كيلوگرم در هكتار و رقم بهار با 5391 كيلوگرم در هكتار عملكرد دانه از شاخص سطح برگ و سرعت رشد محصول بيشتري نيز برخوردار بوده است .

Introduction: Understanding and evaluating the physiological indices of crop growth areparticularly important in terms of analyzing the effective factors on yield and its components, which can aid in determining crop growth stages and assessing yield production (Soleymani Fard et al., 2011). The production and accumulation of dry matter can be studied through crop growth rate (CGR) and relative growth rate (RGR). Environmental stressors exert negative impact on leaf production and expansion. Also with a delay in sowing time, crops are subjected to high or low temperatures, which is often associated with short growth duration, resulting in reduced leaf area index (LAI) (Karim and Siddique 1991). Sowing date is an important aspect of wheat production since it affects various growth and developmental features of the plant such as vernalization, wintering, yield and grain yield components, formation and development of primordial leaf buds and crop canopy. The aim of this study was to determine the appropriate planting date for wheat and investigate the response of some promising spring wheat cultivars to climate changes in Neyshabour- Iran. Materials and Methods: The experiment was carried out at Agricultural Research Station of Neyshabour during 2014-2015 growing season. A split plot experiment, based on randomized complete block design with three replications was performed to investigate the effects of planting date on wheat physiological characteristics. The main plots belonged to three planting dates (October 11th, November 10th, December 10th), while the subplots belonged to different spring wheat cultivars (Chamran, Pishtaz, Bahar, Sirvan, Sivand and Parsi). In order to determine physiological characteristics, quadrat sampling was carried out with a 20×60 cm frame, at 6 growth stages: tillering, stem elongation, booting, heading, pollination and ripening. Dry matter accumulation (DMA), leaf area index (LAI) and crop growth rate (CGR)were calculated using the following equations based on growing degree day: DMA(g.m-2)=exp(a+bx+cx2) (1) LAI=(a+bx+cx2) (2) CGR(g.m-2.10GDD-1)=(b+2cx)exp(a+bx+cx2) (3) First rows of each plot were left unharvested in order to minimize border effect. Random sample of plants was chosen from two middle rows (0.3 m2) to record yield components. Results and Discussion: The results of statistical analysis showed that sowing date had a significant effect on plant height, number of spikes per square meter, number of grains per spike, grain yield and average CGR. Delayed sowing decreased LAI, CGR and DMA of wheat cultivars. The trend of changes for LAI over the growing season indicated that delayed sowing reduced maximum LAI where the highest LAI (4.08) was recorded on Oct. 11 sowing date, whereas December sowing date gave the lowest LAI (2.41). Moreover, under the late seeding conditions, LAI reached its maximum values faster and then dropped more rapidly than earlier seeding dates (Fig. 3). Amongst the tested cultivars, Bahar exhibited the greatest values of DMA, CGR and plant height. The December planting date resulted in the lowest DMA levels amongst the cultivars, which is attributable to the reduced tillering period and lower plant density. Typically, earlier sowing dates than later ones tend to coincide with favorable environmental conditions for plant growth, which is associated with a faster leaf expansion that can consequently lead to an increased solar radiation absorption by plant and thereby higher dry matter production (Jospeh et al.,1985). The effect of delayed cropping on wheat cultivars grain yield was significant. The greatest grain yield (6113 kg.ha-1) was obtained when wheat cultivars were sown on Oct. 11, while the lowest value of grain yield (4124 kg.ha-1) was recorded at the planting date of Dec. 10 (Table 3). The analysis of grain yield correlation with its components demonstrated that spike numbers per square meter was most correlated with grain yield (Table 5). This revealed that spike number reduction was the main cause of grain yield decline in delayed planting. There was a positive correlation between grain yield and average CGR. Conclusion: The findings of this research showed that wheat cultivars, when had more time available for growth and development during the growing season, produced greater numbers of spike per square meter and as a result were likely to give higher grain yields. Under Neyshabour climate conditions, bread wheat common cultivars are recommended to be sown in October to achieve higher grain yields.