Determination of Optimum Transplanting Date for Double Cropping of Rice (Oryza sativa L. CV. Tarom Mahalli) in Mazandaran

Timely transplanting is one of the major objectives of success in double cropping of rice. To determine the best transplanting dates for double cropping of Tarom mahalli in Mazandaran, a field experiment was carried out in a Randomized Complete Block Design with three replicaties in Amol in 2014. Treatments were: 24 transplanting dates beginning from June 28 to September 5 with intervals of three days. The results of analysis of variance indicated that there were significant differences among different transplanting dates for all agronomic traits and grain yield at 1% probability levels. Delaying transplanting increased unfilled grain number per panicle and decreased other agronomic traits including seed yield. The highest grain yield (with an average of 3975.2 kg.ha-1) was obtained at 1st of July transplanting date. This was due to the increase in the number of seeds (80.3), number of filled seed per panicle (72) and panicle number per plant (18.3). The lowest grain yield (with an average of 38.5 kg.ha-1) was obtained at the 5th of September transplanting. Early transplanting decreased days to different phonological stages (days to tillering, 50% flowering and maturity). Delay in transplanting, however, reduced daily temperature, increased number of days to the developmental stages and thus decreased seed yield. Early July transplanting due to suitable temperatures and radiation for flowering and lack of heavy rainfall increased seed yield of rice. It could be concluded that transplanting from the 28th of June to the 10th of July can be considered as the optimum transplanting date for double cropping of rice (var. Tarom mahalli) at Amol climatic conditions.