Increased productivity of rice-based cropping systems in Lao PDR, Cambodia and Australia

• National Agriculture and Forestry Research Institute, Laos
• International Rice Research Institute, Philippines
• Cambodia Agricultural Research and Development Institute, Cambodia
• CRC for Sustainable Rice Production, Australia

In Lao PDR and Cambodia, rice is the staple foodstuff and also the most important crop economically. The most common rice-growing system in these countries is lowland and rain-fed. Most rice grown in this way is consumed directly by the subsistence farmers who grow it. There are few inputs to the system, and the productivity is low. One crop is grown per year, during the wet season. Poor soil nutrients and periodic droughts are also constraints. There is little doubt that yields could increase if the farmers could grow rice cultivars that are productive even under conditions of reduced water and low soil fertility. Laos and Cambodia are still new at breeding rice and systematic research does not take place.

However, there have recently been changes in the rice cultivars used, with a tendency towards shorter-duration cultivars, planting seed earlier and hence earlier harvesting. This opens the possibility of growing a second crop (of rice or another plant). Another option is the development of direct-seeding technologies, which eliminate the need to transplant rice seedlings - a procedure that can result in losses. But a disadvantage of direct seeding is that weeds compete with the rice. The project examined planting methods, direct seeding and the development of suitable cultivars for use in Laos and Cambodia. In Australia, the problems are different, and cultivars are required that can grow well during the early part of the season when it is cooler. This issue was also examined, keeping in mind that such cultivars could also benefit areas of northern Laos.

Project focuses were to improve rice-breeding and agronomic techniques in order to increase productivity and improve stability, mainly in lowland rice-based cropping systems in Lao PDR and Cambodia.

The first of five subprojects concentrated on breeding strategies for cultivars in rain-fed lowland systems, and which could cope with low fertility and drought - using a screening method developed in Thailand. The second subproject determined the risks and benefits of various rice-based double cropping systems. Water balance components were evaluated as part of this work.

In the third subproject, scientists focused on finding cultivars suited to direct seeding, and developing appropriate methods to establish them in different conditions of water availability. They sought reliable direct-seed technologies for lowland rice systems in Laos.

The fourth sub-project aimed to increase the productivity of dry-season irrigated rice - identifying the climatic constraints that distinguish between northern and southern Laos. The scientists assessed the effect of different planting times in different regions, then conducted experiments to determine the interaction between planting time and cultivar, and the requirements of different cultivars for particular conditions, especially low temperature. This work also took Australian needs into account.

The final sub-project integrated information on climate, topography and soils in Laos and used it to produce agro-ecological maps. Much of the information, derived from various Lao agencies, had never been combined and systematically processed into computer-compatible formats. GIS technology was also used. Combining GIS with crop growth models would help to determine the best rice-growing environments. Agro-ecological maps were upgraded during the project, and areas suitable for other crops were also delineated.

The project was successful in developing a method for reliable and routine screening of relatively large numbers of lines for drought tolerance, and for crossing the best drought-tolerant lines with lines of high quality and high yield potential. The researchers generated lines resilient to drought that yield well in good years and have quality characters desired by the farmers. The lines were tested widely across the rainfed conditions. The result for the genotype x environment interactions indicate that testing over six locations for two years is needed to identify improved varieties for the rainfed lowlands.
The new approaches have been incorporated into the breeding programs in Laos and Cambodia. In addition, Lao rice breeders are now trained to properly document, electronically, the pedigree of the breeding program as a basis for improved efficiency and breeding progress. A manual titled Breeding rice for drought-prone environments, published by IRRI is available on line at

http://hdl.handle.net/123456789/210

Increasingly labour is becoming costly and unavailable for transplanting rice. In Laos, the project developed direct-seeding technology to replace transplanting, particularly in dry-season irrigated rice. This method, requiring less labour and using high seed rates and row seeding, can still reasonably control weeds, and yields are consistently high in the dry season. Farmers in the Vientiane Plains now use the technology. However direct seeding is more problematic in the wet season, due to difficulties in water level control in paddies, and weed competition. Thus in the wet season the technique should be confined to areas where weeds are not the main problem and drainage is good.
In Cambodia, the project examined the varietal requirement for direct-seeding systems. Extensive evaluations showed that under favourable conditions and with good weed control, yield from direct seeding was often slightly higher than the crop established from transplanting. The possibility of intensifying the cropping cycle in Cambodia's rainfed lowlands was tested by double cropping rice, and by rice-mungbean double cropping in early wet season and wet season. Results indicate that rice-rice double cropping is a feasible option for the more favourable part of the rainfed lowlands, particularly where supplementary irrigation is available.
In central and southern Laos double cropping of rice is possible in most lowland areas where irrigation water is available in the dry season. Earlier maturing rice varieties are needed for use in the first planting of the rice - rice system. Intensification of rice is difficult in the high altitude areas in northern Laos (altitude greater than 500 m) where low temperature (monthly minimum temperature below 120C) can damage rice establishment. In these conditions a second rice crop must be sown in November before the onset of the colder conditions. Early maturing varieties were developed to facilitate the planting of a second crop in this window. Often irrigation water is not available to establish the crop in November, so the project developed a simple nursery system to protect the young plants from the cold temperatures.
The project developed a number of agro-ecological maps for Laos to define cropping zones. The maps are based on GIS and use information on temperature (available in CD), rainfall and potential evapo-transpiration to define cropping patterns such as the period of wet season, identification of hot months for any locations in Laos. The maps have been used to identify areas where rice sowing in December is risky due to frequent low temperatures. The project also gained a better estimate of paddy water environments for mapping. These maps are of potential use by decision makers in planning and targeting research for Laos.
In Australia a screening method for identifying cold tolerance was developed. A number of cold-tolerant varieties were identified, which have been introduced into the breeding program at Yanco Agriculture Institute.