The Effect of Photosynthetic Characteristics and Grain Yield of Different Growth Habit of Wheat Cultivars to Early, usual and Delayed Planting Dates

IntroductionIn recent decades, the introduction of high-yielding cultivars under optimal conditions has been the main focus of grain research programs. The identification of wheat cultivars that have acceptable yields on different planting dates has been taken into account.Materials and MethodsThe present split-plot test was performed with three replications in two cropping years, 2016-2017 and 2017-2018. The main factor included three planting dates (October 20, November 20, and December 20 as early, normal, and delayed planting dates), and the sub-factor included six wheat cultivars (Zare with winter growth habits, Heidari, Pishgam, and Alvand with facultative growth habits, and Sirvan and Pishtaz with spring growth habits). The soil was sampled from a depth of 0 to 30 cm before the experiment, and the physical and chemical traits of the soil were determined. Land preparation steps were performed before the experiment. For this purpose, a land area of 1500 m2 was plowed by a reversible plow and then leveled. Fertilizer application was performed based on the soil experiment results as 100 kg.ha-1 of triple superphosphate, 100 kg.ha-1 of potassium sulfate, and 100 kg.ha-1 of urea before planting. The rest of the urea fertilizer (200 kg.ha-1) was applied at the stage of stem emergence and the beginning of anthesis wheat. Iron, zinc, and manganese fertilizers were also used from their sulfate sources at the rate of 0.2%, which were sprayed in two stages at the beginning of stalking and spiking. Each plot was 5 m long and 2 m wide and consisted of 8 planting rows at a distance of 25 cm. A distance of 50 cm was considered between the two sub-plots and 1 m between the two main plots. The required seed for each experimental plot was determined and distributed based on the density of 400 seeds per m2 based on the weight of 1000 seeds of each cultivar. Irrigation was performed immediately after planting. Agricultural care was applied uniformly, including pest, disease, and weed control. In each subplot, 50 cm from the beginning and end of the rows was considered as the margin. All data were subjected to ANOVA using the GLM procedure of SAS (SAS 9.1) and means were compared by using the Duncan test at 5% probability level.Results and DiscussionThe results showed that delayed planting reduced nutrient uptake and increased the extinction coefficient. Radiation use efficiency on the planting date of December 20 showed a reduction of 27% and 25%, compared to the planting date of October 20 in 2016-2017 and 2017-2018, respectively. Also, on December 20, Sirvan and Pishtaz cultivars with spring growth habits showed lower extinction coefficients and higher photosynthesis rates than winter and facultative cultivars. On October 20 and November 20, the highest grain yield was obtained in cultivars with winter and facultative growth habits. On December 20, the grain yield was higher in cultivars with facultative and spring growth habits than in winter cultivars. Late planting of wheat cultivars with winter growth type, which must receive low temperatures for Vernalization, is very risky. Because delaying planting may lead to a sharp decrease in yield. These negative consequences of the delay in planting may have occurred through disruption of absorption of water, nutrients, and absorption of active photosynthetic radiation. Late cultivation shortens the vegetative growth period and the plant enters the reproductive stage prematurely, and then the plant faces a lack of photosynthetic resources. Also, the grain filling period is faced with drought and heat stress at the end of the season and this final stress causes a sharp decrease in yield.ConclusionIn general, the delayed planting significantly reduced grain yield, especially in cultivars with winter growth habits. Therefore, it is recommended to use intermediate and spring cultivars for delayed cultivation.