Abstract :
[en] In the Democratic Republic of Congo (DRC) as in other sub-Saharan African (SSA) countries, small farms face the problem of low yields. To meet the challenge of stably and sustainably increasing production, some smallholders are turning to integrated agriculture aquaculture (IAA) production systems developed in South-East Asia. It is based on the exchange of nutrient flows between different subsystems among which fish ponds play a key role. It allows small farms to be less dependent on external resources, increasing profitability. However, the expected results are not yet visible in SSA. The objective of this thesis was to identify which levers can be used to optimize overall production at the farm level in the humid tropics in an African socio-economical context, using the periphery of Kinshasa as a case study. We hypothesized that the level of integration of flows determines the stability of IAA farms, focusing on nitrogen (N), both in terms of quantity and quality, as it is the major limiting factor in both terrestrial and aquatic production.
A survey of 150 integrated agricultural farms in two peri-urban and one rural area of Kinshasa helped to understand how ponds are managed in the integrated systems. A subsequent monitoring of 11 integrated agriculture aquaculture farms for eighteen months with at least two visits per month helped to understand the functioning, the strengths and the weaknesses in the technical and economic organization of IAA farms. In order to quantify and propose a more efficient use of N flows, a mathematical model has been developed. Finally, experiments with locally available resources were carried out to improve efficient use of N flow from pig at the farm level; namely by adding an insect larvae production subsystem in the IAA farms.
Results indicated that 79% of fish ponds in Kinshasa were located on farms integrating fish with livestock (mainly pigs) and/or vegetable farming. No striking difference in farm characteristics between urban and rural farms was denoted, except for fish feeding practices. IAA is generally applied in small farms with limited financial resources and some of them are unable to generate profits, although they all have a positive gross margin. Due to the lack of commercial feed for feeding fish, farm wastes and agro-industrial by-products are widely used as fish feed despite their low nutritional value, especially regarding the protein content and nutritive value of fish. At least eleven possible flows can be exploited with the three main subsystems, i.e. fish ponds, pigsties and vegetable beds, present on a farm with a relatively high use of pig manure as fertilizer for vegetable crops and as an indirect feed protein input through primary production in the fish food chain. The level of education and the involvement of the farm owner have proven to be crucial factors that can allow a better organization of the farm both technically and financially and take maximum advantage of the complementarity of flows between farm components. Losses of N due to poor management of some flows between components have been noted, especially during the harvesting and storage of pig manure which often requires additional labour. Nevertheless, a more appropriate management of N outflows from pigs, which were evaluated at 14gN/pig and 20gN/pig per day, for fecal and urinary forms respectively, by the mathematical model, can help farmers to reduce N losses. For instance, raising pigs above ponds has been shown to be much more effective in minimizing N flow losses and handling requirements due to the natural collection of both feces and urine, which is often difficult in rural and peri-urban pigsties. It also allows farmers to reduce pond density per are of pond in the farm. Feces can also be harvested and used effectively as a substrate for the production of insect larvae, in mixture with agro-industrial wastes. Indeed, feces contain not only N but also undigested proteins and bacteria. They can be used more efficiently to produce a protein source and lead to the design of a new IAA system. In this system the natural production of flies larvae, whose growth limiting factor is probably lysine, could be improved by mixing pig manure with brewers' grains as locally available substrates. The produced larvae with a good amino acid profile can then be used as a complement to fish feed. At the farm level, a prototype infrastructure for maggot production was built directly on the ponds and allowed intensive production, natural harvesting of maggot in the ponds and reduced requirements for handling the manure by the farmers.
In conclusion, integrated agriculture aquaculture systems as applied in the humid tropics of the DRC are able to fulfill their promises of stabilizing production and turning farms profitable. This goal may be achieved if farmers apply a thoughtful strategy for labour management in the farm and get personally involved in the farm’s activities. Farmers need also to focus on reducing N losses through N flows management between subsystem in the farms. They can give particular attention to the pig density and the use of pig manure in the other subsystems. Finally farmers can use the solution proposed by the simulation model according to the available resources and its environment.
