Fissured grain and head rice yield of crops harvested manually or by combine at different ripening stages in Cambodia

Abstract

Combine has been well adopted by smallholders in lowlands of Cambodia and is contributing to the development of mechanized rice production for commercial purposes. Broken rice is a major issue for the commercial rice product, and fissured grain at harvest leads to broken rice and lowers head rice yield (HRY) during milling. Factors that determine grain fissures and broken rice were obtained from three studies: an on-farm study of fissured grain, a research station experiment of fissured grain and broken rice harvested at different ripening stages and a mill study of fissured and broken rice during drying and milling processes in Cambodia. There was significant variation in fissured rice percentage among 20 farms sampled, and the fissured grain was negatively correlated with grain moisture content at harvest. Time of harvesting was crucial, as delay in harvesting after 25 days after flowering (DAF) often resulted in lower grain moisture content and higher fissured grain, which subsequently reduced HRY. However, the optimum time of harvesting varied across four seasons for crops harvested manually or by combine. In some years, crops harvested at 35 DAF had rather low per cent fissured grain with subsequently high HRY, this may have been associated with slightly lower temperatures. The mill study showed that fissured grain developed during the drying, storage and milling processes. It is concluded that while grain moisture content at the time of harvest may be used as an indication of subsequent HRY, the latter was more strongly related to fissured grain at harvest.

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

“…With mean temperature around harvesting time of 32°C in the DS, the same heat sum would be achieved in 22 days after flowering. In WS in Phnom Penh, Cambodia, the mean temperature for 15 days prior to harvest was 27.0-29.0°C (Bunna, Sinath, et al, 2019), which was slightly lower than 28.5-29.8°C recorded for WS and much lower than 30.3-33.5°C recorded for DS in the present experiments. The lower temperature in Cambodia was associated with later harvesting in November-early December compared with harvesting in October in the present WS experiments in Laos.…”

“…The lower temperature in Cambodia was associated with later harvesting in November-early December compared with harvesting in October in the present WS experiments in Laos. The heat sum calculated with 10°C base temperature for the Cambodian case is about 420 and 500 degree-days for harvesting at 25 and 30 days after flowering (Bunna, Sinath, et al, 2019). The head rice recovery at these two harvests were similar in their experiments, suggesting the maximum heat sum beyond which head rice recovery may decline would be around 500 degree-days.…”

Research strategies for mechanised production of rice in transition from subsistence to commercial agriculture: a case study from Khammouan in Lao PDR

“…Their study also indicated that combine harvested grain yield was similar to hand harvested yield and grain harvesting loss was about 1.5% of the total yield, which was less than the total loss for manual harvested crops when the losses during threshing and handling of paddies was included. Grain quality of combine-harvested crops is as good as that of manually harvested crops when harvested paddies are dried properly (Bunna et al, 2018(Bunna et al, , 2019Vongxayya et al, 2019). Often combine harvested crops are dried artificially while manually harvested crops are sun dried, then higher head rice yield is obtained in combine-harvested crops (Vongxayya et al, 2019), paving the way for improved grain quality and marketing.…”

“…Broken rice during milling is reduced when rice is dried using flatbed dryers rather than sun-drying, and this resulted in head rice yield of about 50% compared with less than 40% with sundrying (Vongxayya et al, 2019;Xangsayasane et al, 2019b) . The importance of using artificial drying was recognised particularly when crops were harvested early during the ripening phase and grain moisture content was still high (Bunna et al, 2019). With sun drying, the paddy needs to be turned over every 2 hr or needs to dry in thin layers of 2 cm or less to maintain high head rice yield.…”

“…Introduction of artificial dryer improves head rice yield (Vongxayya et al, 2019;Xangsayasane et al, 2019b), and this would improve marketability of the rice grain. While combine harvesting may not provide better head rice yield compared to hand harvested crop (Bunna et al, 2019), combine harvested paddies are often dried artificially to minimize the risk of grain being spoilt with rain events which may occur when sun drying, and the artificial drying improves head rice yield (Vongxayya et al, 2019;Xangsayasane et al, 2019b).…”