Effectiveness of a solar grain dryer for drying paddy seed in Bangladesh

Proper and timely drying is needed for producing quality paddy seed. Open sun drying is often produced seed with foreign materials. Solar dryer produced by science for society (S4S), India might be suitable for country like Bangladesh. Therefore, an attempt was taken to evaluate S4S seed dryer at the Workshop, Department of Farm Power and Machinery, Bangladesh Agricultural University, Mymensingh. In this experiment, the spatial and temporal distribution of temperature and moisture in S4S solar grain dryer was investigated and the seed quality was also evaluated. The dryer performance was evaluated with six trials in Boro season from May 10 to June 6, 2017 and with three trials in Aman season from November 7 to 11, 2017. Paddy seed samples were also dried by open sun drying in Aman season to compare the performance of the dryer. Depending on paddy variety the capacity of the dryer was 42 to 55kg/batch. Drying rate, drying efficiency and percent of drying loss were calculated. The germination rate and vigor index were also calculated to evaluate the quality of paddy seed. Results revealed that temperature distribution at different locations inside of the dryer was fluctuated within a narrow band. In Boro season, drying time was 13.5 to 29 hours for reducing moisture content from 24.27±3.49 to 12.1±0.86% in. On the otherhand, the drying time required to reduce moisture content of paddy from 16.07±0.06 to 11.00±0.11% was 6.5 to 8 hours in Aman season where in case of sun drying, moisture content was reduced from 16.07±0.06 to 11.19±0.14% within 7.5 to 8 hours. In Boro season, the drying rate and drying efficiency of S4S solar grain dryer were 0.67±0.11% MC/hr and 48.23±6.84%, respectively. The average drying loss measured in S4S solar grain dryer was 0.58±0.19%, respectively in Boro season. In Aman season, the drying rate and drying efficiency of S4S solar grain dryer was found 0.70±0.07%MC/hr and 27.67±3.61%, respectively. The average drying loss measured in S4S solar grain dryer (0.41±0.55 %) was lower than sun drying (2.12±1.24%) in Aman season. The germination and vigor index of S4S solar grain dryer dried paddy seeds were satisfactory ranged 82 to 97% and 1638 to 2232 compared to sun drying ranged 79 to 80% and 1738 to 1973. Thus, paddy seeds can be dried in S4S solar grain dryer without impairing germination and vigor of seed. Farmers can get better quality seed when using S4S solar grain dryer