Our study made a comparative analysis of the different drying practices used in Vietnam, Cambodia, the Philippines, and Myanmar. Quantification of energy efficiency, greenhouse gas (GHG) emissions, and cost-benefits generated the implications for selecting the optimal drying practice corresponding to various techno-economic indicators, environments, scales of operations, and market demands. Using a reversible airflow flatbed dryer with a capacity of 20 tons of paddy per batch was found to be the best option in terms of cost-benefit, labor operation, and energy efficiency. On the other hand, a recirculating columnar dryer requires 15% higher energy consumption but only needs 20-50% of the floor area; while a solar bubble dryer still needs optimization in terms of reduced investment cost and labor requirement. A two-stage drying system including a fluidized-bed and ten recirculating columnar dryers is an optimal option with the lowest drying cost and labor use when aiming at an industrial capacity of greater than 200 t/day. Nevertheless, the energy consumption and GHG emission of the solar bubble dryer are lower by more than 50% than that of other practices. In addition to the comparative analysis of these techno-economic factors, this research also identified the trajectories of developing paddy drying technologies that are aligned with different postharvest systems identified as subsistence farming for own consumption, surplus farming for local markets, and surplus farming for premium and export markets. The study recommends paddy drying strategies in Southeast Asian countries that could be applied in other rice-production regions as well.

Paddy rice was sun dried in Cambodia in 2004 using a range of methods practiced by local rice farmers. For each treatment in the experiment, a grain sample at about 22% moisture (typical harvest moisture content) was sun dried between 8 a.m. and 4 p.m. During experiments, the grain moisture content was measured at regular intervals. The grain varieties used, bed depths, stirring of the grain, bulk tempering after drying and the drying pads had significant effects on the drying time. Drying was faster when bed depth was reduced, regularly stirred but not shaded or covered and when the drying was carried out on a porous pad. Damage to the dried grain was reduced when the bed was thin, stirred and shaded and when the drying was slow on pads with less air circulation.

A mathematical model describing the heat and moisture transfer within a solar drying system of rice was formulated. A numerical solution using MATLAB was implemented due to the many coupled PDEs and nonlinear algebraic equations. The model was checked for a range of the space steps and by comparison to analytical solutions for completed situations and was shown to contain no significant numerical errors. After estimating the best values and uncertainties of the system inputs the model was validated by comparison with experimental data for solar drying of rice. It was shown to be a very good mechanistic tool with advantages of simplicity and practical accuracy. The model accurately predicted the drying time and the temperature, and moisture content (MC) within the bed during drying except when a polystyrene drying pad was used. However, the model did not predict the experimental bed water activity (relative humidity) consistently well.

Laser-controlled land leveling (LLL) can help improve rice production's spatial and temporal management, leading to optimized water and crop management. This research resulted in sustainable performance indicators to illustrate that LLL is a sustainable technology for rice production. The assessment was conducted in Cambodia, the Philippines, Thailand, Vietnam, and India. Benefits of LLL include saving land use, water, and agronomic inputs, increasing yield, and decreasing postharvest losses resulting in saving energy of 3.0–6.9 GJ ha−1 and decreasing emissions by 1151–1486 kg CO2-eq ha−1. Additionally, LLL application can obtain a net profit of USD 52–84 ha−1 per rice production season in the countries studied. The result demonstrated that LLL is a sustainable technology as well as strongly supports sustainable rice production. The study would lead to better adoption of this technology through its evidence-based promotion.

Rice grain conditions within the sun-drying bed predicted by a mathematical model during drying were used to relate drying parameters to the head rice yield (HRY) which is the key rice quality metric. A number of parameters were derived to characterise the mechanisms of grain fissures and breakage postulated in the literature, and the model was used to estimate these parameters. These parameters were then regressed against the HRY experimental data to determine the contributing mechanisms. An increase in bed temperature, the maximum temperature at the top of the bed, the size of the moisture content gradients within a rice grain and the difference from the critical point for drying were all found to negatively affect HRY. By stirring the bed regularly and covering and shading the bed during the hottest parts of the day, HRY can be significantly increased leading to better returns to the farmer.