|Background and Goal: The planting date is an important factor affecting vegetative and reproductive characteristics, the length of the growing season, and ultimately the quantity and quality of cottonseed. When the planting date is delayed, the flowering period coincides with high temperatures, increasing the number of bolls dropped and decreasing the number of bolls per plant. Since the new cotton varieties (Armaghan, Shayan, Khorshid, Khordad and Sajdi) are usually early maturing and use less water, they are accepted by farmers. However, in some cases they are planted too late. Since the proper planting date for these varieties has not been determined, this project was undertaken to determine the optimal planting date for new cotton varieties.|
Material and Methods: Five varieties named Armaghan, Shayan, Khorshid, Khordad, and Sajedi (as subplots) were planted on three planting dates: May 10, May 31, and June 20 (as main plots) with four rows on each plot. This experiment was conducted using a split-plot experiment based on a randomized complete block design with three replications at the Neyshabur Agriculture and Natural Resources Research Station in 2019 and 2020. Irrigation was done using a tape (negative pressure irrigation system) with a drip spacing of 20 centimeters and a flow rate of 4 liters per hour. Five plants were randomly selected. The parameters measured were: Number of vegetative and reproductive branches per plant, plant height, number of immature and mature bolls per plant, weight of bolls, cotton seed yield. Analysis of variance and comparison of the mean values of the traits were performed using MSTATC and Excel and least significant difference (LSD).
Results: The results showed that the maximum number of closed bolls and the lowest number of vegetative and reproductive branches, number of open bolls and cotton seed yield belonged to the last planting date. On average, delaying the planting date reduced the cotton seed yield by 50.3%. The yield of cottonseed decreased by as much as 85.4% on June 20. The lowest and the highest yield of cottonseed were obtained in Armaghan variety on the last planting date and in Sajedi variety on the first planting date. The highest yield (3971.7 kg/ha) was obtained in Sajedi on the first planting date. Also, the lowest yield in Sedd cotton, which decreased due to late sowing, was obtained from Sajedi variety.
Conclusion: the results of the present study show that in Neyshabur area the planting of the mentioned varieties should be done by June 10, and further delay in sowing leads to a sharp decrease in yield (in some years due to the damage caused by the early autumn cold). However, the studied cultivars responded differently in this regard, and cultivars such as Sajdi and Khorshid, which had the highest yields overall in two years, showed the least decline compared to Armaghan, Shayan and Khordad cultivars.