Soil fertility management for organic rice production in the Lao PDR

Rice is the most important agricultural commodity of the Lao People's Democratic Republic (Lao PDR), produced largely using traditional methods with limited inputs of fertilizers and other chemicals. The country has a wide diversity in rice production systems and rice varieties, with over 3000 different varieties recorded. The rich diversity and the production environment and methods are favorable for organic rice production. Investigations were carried out to describe soil fertility conditions, management practices, opportunities and problems associated with organic production methods for rice. Soils used for rice production are mostly of low fertility, with low organic matter and N-availability. In spite of this, virtually no fertilizer inputs are used for upland rice production. Inorganic fertilizer inputs for lowland rice production have increased rapidly over the past decade, but are still below 20 kg ha−1. The most important nutrient sources are rice straw and manure from buffalo and cattle. Chromolaena odorata plays an important role in nutrient cycling in upland rice systems and is sometimes added to lowland fields. In a range of fertility management studies, yield increase ranged from 2 to 89% for manure, straw or rice husk applied at modest rates (3 t ha−1), 32-156% for modest rates of inorganic fertilizer (60 kg N ha−1) and 36-167% for combined application of manure or crop residues with inorganic fertilizer. The response to locally produced commercial organic fertilizer was poor. The most promising inputs and strategies available to optimize yields in organic rice production systems are (1) optimizing use of locally available nutrients, mostly from manure, crop residues and weed biomass, (2) N addition through green manure and legumes growing in rotation and (3) additions of P through guano or rock-phosphate. The Lao PDR is fortunate to have substantial bat guano deposits in limestone caves. Extensive experience is available on straw and husk management for lowland systems and green manure species for upland production system

Farmer participatory variety selection conducted in high- and low-toposequence multi-location trials for improving rainfed lowland rice in Lao PDR

Lowland rice in Lao PDR is predominantly grown under drought-prone, rainfed conditions in the wet season. We utilised a farmer participatory variety selection (PVS) approach in combination with multi-location yield trials (MLTs) conducted in high- and low-toposequence positions to test advanced breeding lines with the aim of improving the efficiency of the rice-breeding program and encouraging rapid adoption of improved lines. Upper position fields were utilised to screen for traits for unfavourable environments, including drought resistance, while lower fields were used to target yield potential. Yield was, on average, 13% lower in upper than lower (2.85 t/ha) field positions, and varieties adapted to high-toposequence position were identified. Farmer preference was not associated well with grain yield performance, with a significant positive relationship (r = 0.34*, n = 23) identified only in the Vientiane (VTN) low-toposequence trial; rather, the famers tended to choose lines they believed were best adapted to their own farm. Although a significant relationship existed for both farmer preference (r = 0.42*, n = 23) and grain yield (r = 0.50*, n = 23) in high and low toposequences across all provinces in 2010, this relationship was not significant in VTN, where the high position was low-yielding (1.2 t/ha). By utilising farmer preference information in combination with traditional MLT data, only lines agronomically acceptable to farmers were progressed into a seed-multiplication system for country-wide, farmer yield testing. Thus, the PVS-MLT approach has provided efficient delivery of highly acceptable lines to farmers, which directly contributes to improved efficiency of the rice-breeding program

Farmer participatory varietal selection in Lao lowland rice systems

Participatory variety selection (PVS) is being used by the ACIAR funded UQ-Lowland Laos Project to improve rice varietal adaptation and seed production. The strength of this participatory approach is in allowing farmers’ judgment on grain quality and plant type to enter the breeding process in the final stages, ensuring local adaptation and fostering ownership of the chosen varieties which encourages seed production and distribution. Eating quality especially is an important parameter – probably even more important in Lao PDR – that has caused otherwise suitable varieties to be discarded by farmers. In the absence a of a well-resourced grain quality program to assess early generations, it is a pragmatic middle way. The two provinces that returned data differed in varietal preference. Vientiane Province selected solely TDK varieties, which were bred in Vientiane Province (TDK9, TDK11, TDK 25 and TDK42). Champassak Province, in southern Lao PDR, selected varieties from a range of sources (TDK8, PNG3, TDK49, TDK1 and TSN7). The methodology in the 2007 wet season was deficient in four ways: eating quality was not assessed (insufficient grain), selection was done solely on plant type and not with yield data, very few women were invited to select in Vientiane Province and the PVS was not conducted in a drought-prone environment. All of these will be addressed in wet season 2008. This will be an ongoing process; as such the ability of farmers, local staff and national staff to conduct and utilize PVS has been improved

Selection of widely adapted lowland rice varieties for wet and dry seasons in Laos

A series of lowland experiments, in the wet season (WS) under rainfed and dry season (DS) under irrigation, was conducted with 23 rice cultivars in four rice growing areas in Laos during the three-year period from 2003 WS to 2005/2006 DS. The objectives were a) to investigate the seasonal effects on cultivar performance in dry and wet season rice productivity in a range of rice growing environments in Laos and b) to identify the appropriate season for cultivar selection in the national rice breeding program. There was significant genotypic variation for grain yield (GY) only in four of ten experiments conducted in the WS. In contrast, genotypic variation for GY in all eight experiments conducted in the dry season was significant. The heritability (h2) for GY in WS experiments was lower (0.46) than the heritability for DS experiments (0.56). The genetic correlation between WS and DS experiments for grain yield was 0.36. While there was significant genotype-by-season interaction, the genotype clustering was not associated with the season and the results indicated that the increased use of DS screening would improve the efficiency of the overall rice variety selection program

Consistency of genotypic performance of lowland rice in wet and dry season in Lao PDR

Lowland rice in Laos as in some other SE Asian countries is grown mostly under rainfed conditions in wet season (WS), but some crops are grown under irrigated conditions in dry season (DS). In Laos, the rice breeding program is concentrating on development of photoperiod insensitive varieties which can be grown in both WS and DS, nevertheless most selection is conducted in WS. In order to determine consistency of genotypic performance between WS and DS, 23 advanced breeding lines and varieties were grown in both seasons for 2-3 years at four locations in the country. All experiments in DS showed significant genotypic variation for grain yield, while genotypic variation was smaller and often not significant in each experiment in WS. The heritability was also higher in DS than in WS. Significant genotype-by-environment interaction was found, and some of this interaction was due to long duration genotypes being affected by extreme temperature conditions in DS particularly at a high altitude location in Northern Laos. Cluster analyses indicate that the genotypic discrimination was large in experiments with intermediate yield levels (mean yield of 2.9-3.8 t/ha). It is concluded that the use of DS trials should be increased to improve the efficiency of selection for widely adapted varieties in the lowland rice breeding program in Laos and other countries of similar growing conditions. Crow

Agro-economic evaluation of fertilizer recommendations for rainfed lowland rice

Abstract not availableS.M. Haefele, N. Sipaseuth, V. Phengsouvanna, K. Dounphady, S. Vongsouth