Water, not nutrients : the major focus of pond-based aquaculture integration within smallholder farms in Asia

Excavated earthen ponds in tropical rain-fed farming systems are typically characterised, and promoted, as culture systems for around which whole-farm nutrient can be more efutilised. Research sites where ponds were common features of smallholder farms in Northeast Thailand, the Mekong Delta, Vietnam and central Bangladesh were identiand participatory research undertaken at the community-level. The research focus was to understand the current role of ponds within farming, and broader livelihood, systems and opportunities for enhancing benesub-sites were located in areas with high and low access to urban areas. At the rain-fed sites, where seasonal water scarcity was an issue (Thailand, Bangladesh), the importance of the pond as an on-farm source of irrigation water was paramount, whereas this was not the case in Vietnam where ponds and associated ditches were more related to a source of landand temporary supply and drainage of water respectively. In Thailand, ponds were generally not originally constructed with a view to optimising culture but rather to support associated dry season horticulture. In recent years their value for, and importance attached to aquaculture, had increased, but still fell far below potential. The importance of using pond water for seasonal cash crops, especially chilli, had become the major strategy among farmers and increasing the focus on, and benefrom, culture were not perceived as being complementary with this. In Bangladesh, ponds were also multipurpose but our analysis also showed interesting dynamic and potential for greater benefrom both the and crop production occurring in the immediate vicinity. In both these sites linkages between nutrients within ponds and surrounding aquaculture were weak and increasing inputs through intensieven seasonal culture was identias a strategy to enhance system productivity and beneThe cost of nutrients for horticulture was identiby farmers as a major problem. Improved mechanisms of reusing nutrients trapped in more intensively managed are therefore important. The production systems in Vietnam are resource intensive compared to the sites in Bangladesh and Thailand and higher levels of water exchange leads to local pollution. Low prices for most cultured herbivorous species has led farmers to prioritise improved systems for indigenous, usually carnivorous species, as a researchable issue. The concept of physically integrating water efreuse through adjacent extensive areas of ditch-dike orchard where a forage could be produced to support higher densities of high value carnivorous was identias a potential opportunity. In common with Bangladesh a signiproportion of farmers raising in Vietnam have commercial expectations and river cat(Pangasius hypothalamus) has been intensisigniin contrast to carp polycultures but this approach is not an option for resource-poorer farmers. The three sites therefore demonstrate a range of situations under which pond-based diversihas occurred, but that overall nutrient efremains poor under both rain-fed and perennially irrigated situations. Approaches that allow complementary intensiof and crop production in both contexts have potential.