Rice milling quality as affected by drying method and harvesting time during ripening in wet and dry seasons

Abstract

Head rice recovery is known to decrease with the delay in harvesting during ripening, but this effect may differ between wet season (WS) and dry season (DS) and among different paddy drying methods. In five experiments, rice was harvested by hand between 25 and 45 days after flowering in DS and WS when temperature around harvest was slightly above and below 30°C, respectively. The highest head rice recovery was generally obtained when rice was harvested at 25 days after 75% flowering. Delaying harvest to 30 days resulted in significant reduction in head rice recovery in 3 out of 7 cases and further delay to 35 days resulted in significant reduction in 8 out of 10 cases. For the crops harvested 25 days after flowering and dried with a flatbed dryer head rice recovery improved compared to sun drying in two experiments. When harvesting was delayed, sun drying tended to reduce head rice recovery compared to artificial drying. Sun drying only in the morning also improved head rice recovery compared to drying for the whole day. For a given drying method, head rice recovery decreased with increase in heat sum from flowering to harvest. It is concluded that rice crops should be harvested in both DS and WS around 25 days after 75% flowering when heat sum with base temperature of 10°C was around 450-500 degreedays. If an artificial dryer is not available, rough rice should be sun dried only in the morning with frequent stirring and mixing to promote more even drying.

Effects of introduction of combine harvester and flatbed dryer on milling quality of three glutinous rice varieties in Lao PDR

“…HRY can be increased in the sun drying with some modifications of the technique. For example, HRY was higher when grains were stirred frequently, drying grain on a mat rather than on concrete (Imoudu & Olufayo, 2000) or drying only in the morning rather than for the whole day (Xangsayasane et al, 2019).…”

“…Combine harvesting results in similar grain yield with only slightly higher grain loss in the field than hand harvesting, but when grain loss during threshing is added, the total grain loss is similar between the two harvesting methods (Bunna et al, 2018). Farmer's net return is greater with combine than with hand harvesting as long as the combine contractor fees are less than 20% of the total rice harvested (Xangsayasane et al, 2019). These findings indicate that adopting combine harvesting service is likely to be beneficial to the farmers, and in fact the number of combines has started to increase sharply in the last few years in Central Laos.…”

“…Combine harvester was introduced only recently in Lao PDR to save labour cost and counters the reduced labour availability in rural areas. Combine harvesting service is spreading in Central Laos as it provides higher CONTACT Darunee Jothityangkoon darcho@kku.ac.th return to farmers compared to traditional hand harvesting (Xangsayasane et al, 2019). Combine grain loss in the field is comparable to hand-harvested crops when grain loss during threshing is added to that harvested by hand (Xangsayasane et al, 2019;Bunna et al, 2018).…”

“…Combine harvesting service is spreading in Central Laos as it provides higher CONTACT Darunee Jothityangkoon darcho@kku.ac.th return to farmers compared to traditional hand harvesting (Xangsayasane et al, 2019). Combine grain loss in the field is comparable to hand-harvested crops when grain loss during threshing is added to that harvested by hand (Xangsayasane et al, 2019;Bunna et al, 2018). The combine harvester has higher speed to harvest grain resulting in more damage grains and slightly lower HRY (Andrews, Siebenmorgen, Vories, Loewer, & Mauromoustakos, 1993).…”

“…Artificial drying in protected conditions with constant supply of heat and constant humidity conditions can reduce cracking and subsequent breakage of grains, particularly if high moisture grains are dried under low humidity conditions (Banaszek & Siebenmorgen, 1990). Combine harvested paddy can be dried in the sun using a mat or dried artificially using mechanical dryer (Xangsayasane et al, 2019) and proper drying techniques to reduce moisture content in rough rice are a key factor in improving milling quality and head rice recovery and hence its commercial value.…”