Agronomic Parameters of High-Altitude Rice Varieties and their Relation to Temperature at Different Growth Stages

Abstract

The warm temperate agro-ecozone or high-altitude rice production areas in Bhutan represent a unique agro-ecology that is specific to adaptation needs of rice varieties. A study was undertaken to consolidate the basic agronomic parameters released and popularly cultivated rice varieties of the high-altitude areas. The agronomic parameters were assessed in relation to the weather in the zone. Ten years' weather data (2009-2018) of Paro Dzongkhag was used to relate the agronomic parameters of rice varieties to temperature and rainfall patterns. Seven improved varieties and one traditional variety were used for this study which was conducted at Tsento-Shari ((2450 masl), Paro in 2019 rice season. 50% flowering and days to maturity which are the two most fundamental indicators of adaptation of rice varieties in the warm temperate agro-ecozone were at 162-181 days and 206-236 days respectively. The mean temperatures in the trial site for 10 years during anthesis was 18.5 ºC against the optimum mean temperature requirement for rice (30-33 ºC). The mean temperature at the ripening phase was found to be 16.5 ºC as against the optimum temperature requirement of 20-25 ºC. Despite a relatively low mean temperature during ripening, all the assessed varieties matured and produced good yield indicating good cold tolerance. Rice farmers in the high-altitude areas normally transplant seedlings at about 90 days old when they are hardy enough and can gain some level of physiological maturity to help cope against low mean temperature at ripening. The mean yield of the eight varieties ranged from 2.01 t/acre to 2.98 t/acre which was higher compared to the national average yield of 1.73 t/acre.