Planting Date Effect on Harvesting time of RD79 Rice Seed Production in Nakhon Sawan Province

Abstract

The cultivation of rice variety RD79 across different regions of the country is constrained by an extended maturity period, which varies according to planting time and cultivation latitude. This study aimed to determine the optimal planting time for RD79 rice in irrigated areas of Nakhon Sawan province, where rice is cultivated continuously during both dry (off-season) and wet (main season) periods. The experiment was conducted at the Nakhon Sawan Rice Seed Center using a randomized complete block design (RCBD) with 24 treatments 4 replications. Rice seedlings were sowed on the 1st and 15th of each month for 12 consecutive months since December 2021 to November 2022. At 15 days after germination, rice seedlings were transplanted into pots with a diameter of 15 inches, each filled with 20 kilograms of soil. Three seedlings were planted per pot. The pots were placed within concrete rings located in the varietal testing plot. Fertilizer was applied twice following the recommended application guidelines. Data were recorded on 50% flowering date, harvesting age, stem growth characteristics, and seed components. The results showed that rice planted on May 1st had the longest average duration to 50% flowering (121 days), with an average day length of 12.35 hours, resulting in the longest physiological harvesting age (151 days) but the lowest yield. Conversely, rice planted on September 15th had the shortest average duration to 50% flowering (82 days), with an average day length of 11.17 hours, resulting in the shortest physiological harvesting age (112 days) and a moderate yield. Recommendations for planting RD79 rice in irrigated areas of Nakhon Sawan province are as follows: First dry-season crop: Planting should be done from early December to early January, resulting in 120-123 days to harvest and the highest yields. Planting should not be delayed beyond mid-January, as both harvesting age and yield will decrease. Second dry-season crop: Planting in early March to early April produces a slightly lower yield and a longer harvesting age (~147 days); therefore, RD79 is not recommended for this season. Wet-season crop: This variety should be planted earlier than other varieties, planting from early July to early August provides relatively high yields and shorter harvesting ages (120-125 days). Planting during May until June is not recommended, especially in May, due to prolonged harvesting age and low yields. For seed production, planting time did not affect the germination rate of RD79 rice seeds.