Ideotyping integrated aquaculture systems to balance soil nutrients.

Due to growing land scarcity and lack of nutrient inputs, African farmers switched from shifting cultivation to continuous cropping and extended crop area by bringing fragile lands such as river banks and hill slopes into production. This accelerated soil fertility decline caused by erosion, harvesting and insufficient nutrient replenishment. We explored the feasibility to reduce nutrient depletion by increasing nutrient utilization efficiencies, while diversifying and increasing food production through the development of integrated aquaculture – agriculture (IAA). Considering the climatic conditions prevailing in Kenyan highlands, aquaculture production scenarios were ideotyped per agro-ecological zone. These aquaculture production scenarios were integrated into existing NUTrient MONitoring (NUTMON) farm surveydata for the area. The nutrient balances and flows of the resulting IAA-systems were compared to present land use.The effects of IAA development on nutrient depletion and total food production were evaluated. With the development of IAA systems, nutrient depletion rates dropped by 23–35%, agricultural production increased by 2–26% and overall farm food production increased by 22–70%. The study demonstrates that from a bio-physical point of view, the development of IAA-systems in Africa is technically possible and could raise soil fertility and total farm production. Further studies that evaluate the economic feasibility and impacts on the livelihood of farming households are recommended

De bijdrage van visvijvers aan de nutriënthuishouding op gemengde kleinschalige landbouwbedrijven

Vijvers kunnen een aanzienlijke bijdrage leveren aan de nutriëntenkringloop op gemenge landbouwbedrijven. Het integreren van water- en landgebonden productie in gemengde bedrijven kan leiden tot een verhoogde efficiëntie van het nutriëntengebruik. Bij evaluatie van de visteelt wordt vaak alleen gekeken naar de oogst zonder aandacht voor andere voordelen van visteelt zoals waterbeschikbaarheid of efficiëntie van nutriëntengebruik. Bovendien verkiezen boeren vaak geformuleerde voeders, hoewel het voordeel voor de oogst hiervan niet evident is in de gemiddelde eenvoudige onbeluchte vijvers. Een onderzoeksproject is gestart om mogelijkheden voor verbetering in kaart te brenge

Exploring the trophic structure in organically fertilized and feed-driven tilapia culture environments using multivariate analyses

Reports of similar yields in manure and feed-driven tilapia culture environments raise questions on food utilization in these environments. The possibility that similar production rates are because of utilization of different foods was investigated using exploratory techniques of multivariate analyses. Using factor analysis, trophic pathways through which food becomes available to fish were explored, and using anova models, water quality, sediment quality and tilapia growth and yields were compared. Conceptual graphic models of the main ecological processes occurring in feed-driven and organically fertilized environments are presented and discussed. In both environments, autotrophic and heterotrophic pathways are important processes that result in the availability of natural foods that are utilized by the fish. Extrapolated fish yield data indicate that with equal nutrient input and stocking density, organically fertilized environments could achieve production rates similar to those in feed-driven environments. The general assumption that supplemental or complete foods are well utilized by tilapia in outdoor stagnant ponds remains challenged, and further research on tilapia feeding behaviour and food selection in feed-and organic fertilizer-driven environments is needed