Makara Ouk

Increased productivity of rainfed lowland rice cropping systems of the Mekong region

Abstract. Rice in Thailand, Laos and Cambodia (the Mekong region) is grown mostly as a mono crop once a year in the wet season in the rainfed lowlands. Some lowland areas have access to irrigation water, and rice double cropping is practised while non-rice crops are grown in a limited area in the dry season after harvesting wet season rice. In all cases wet season rice is grown mostly for subsistence under rainfed with low input, and combined with low soil fertility and frequent occurrence of drought, the yield is generally low with a mean of 2.5 t/ha and the yield increase was slow in recent years. More recently demand for labour in the regional centres has caused labour shortages in the rural area and rice crops may not be managed in the traditional manner such as the practice of manually transplanting of rice seedlings. For the last two decades research efforts have been made to minimise the adverse effect of abiotic factors and to meet the changing nature of the socioeconomic environment, resulting in increased understanding of factors determining productivity of rainfed lowland rice and the cropping systems based on it. This review describes such achievements in five sections – water environment characterisation to quantify drought problems, soil environment and fertiliser management, direct seeding to develop technology to cope with the labour shortage, variety improvement for rainfed lowland rice in drought-prone environment, and crop intensification and diversification that shift practices from traditional subsistence agriculture to more market-oriented agriculture. Each section is concluded with issues for future research need. The last section of the paper describes future research challenges for the rainfed rice-based lowland cropping systems in the Mekong region and possible implication on rainfed lowland rice system on other regions.

Quality evaluation, fatty acid analysis and untargeted profiling of volatiles in Cambodian rice

This study provides the first investigation of the physical traits, pasting properties and volatile compounds of Cambodian rice cultivars, including traditional, improved, and improved traditional varieties, allowing for their differentiation as high and low quality rice. Analysis of the grain quality traits illustrates interesting features of traditional varieties and correlations between traits that assist with understanding texture. Untargeted profiling of volatile compounds shows that high quality fragrant varieties not only contain 2-acetyl-1-pyrroline but also several other compounds, including aldehydes, alcohols and 2-alkylfurans that contribute to overall aroma. Moreover, low odour threshold volatile compounds, which can be derived from the oxidation of unsaturated fatty acids, were more abundant in the fragrant varieties. The percentage area of both oleic and linoleic acid were found to be significantly different among the rice varieties tested. Such findings suggest that unsaturated fatty acids in milled rice contribute to rice fragrance, and thereby to overall quality.

Farmers’ Management Practices and Grain Yield of Rice in Response to Different Water Environments in Kamping Puoy Irrigation Rehabilitation Area in Northwest Cambodia

Abstract The farmers’ management practices and grain yield were examined in the consecutive 4 cropping seasons from wet season rice (WSR) in 2008 to dry season rice (DSR) in 2010 across upstream, midstream and downstream fields, along two secondary drainage canals (located either upstream or downstream side along the main canal) in the Kamping Puoy Irrigation Rehabilitation area (KPIR). In WSR, standing water depth was much deeper in downstream fields where medium and late maturing varieties were planted from May than in upstream fields where early and early medium maturing varieties were planted later (mostly in July and August). In DSR there was less difference in water conditions between upstream and downstream fields and variation in planting and harvesting time was small. As the area percentage of fields where DSR was introduced increased from 2008 (54%) to 2010 (100%), planting time in WSR was later (e.g., from May to July) with declining proportion of dry seeding method and mid-season tillage. Grain yield was low in DSR, particularly in 2010 (287 and 247 g m-2 in 2009 and 2010 on average, respectively), due to insufficient weed control and small amount of fertilizer, and the yield was lowest in fields which practiced DSR for the first time. Grain yield in WSR (286 and 291 g m-2 in 2008 and 2009 respectively) increased by transplanting, use of high yielding Raing Chey variety, and application of a larger amount of N chemical fertilizer. These findings indicated that the agriculture extension support to farmers, particularly in DSR, is a key important factor for rice yield improvement in KPIR.

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.