The total amount of nitrogen and phosphorus in animal manures, and the proportion of this amount that becomes available as dissolved inorganic nitrogen and phosphorus within a month after manures are added to water were examined in the context of fertilization guidelines for pond aquaculture. A literature study was conducted to synthesize information on the dry matter, total nitrogen and total phosphorus contents, and the biochemical oxygen demands of different manures. This information was used to compile a fertilizer database and to examine dry matter-nutrient relationships for different manures. Significantly high correlations between dry matter and total nitrogen, and between dry matter and total phosphorus were observed for poultry manure, and different forms of beef and dairy cattle manures. These relationships can be used to estimate the nutrient contents of manures if the dry matter contents are measured. A laboratory experiment was conducted to determine the amount of nitrogen and phosphorus that becomes available as dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP) over a five week period when poultry, swine and dairy manures are added to water. Mean DIN and DIP concentrations reached highest levels on the 5th day after manure addition for all the manures. These concentrations corresponded to 60.5, 49.5 and 30.1% of the total nitrogen and 78.4, 77.4 and 58% of the total phosphorus supplied by poultry, swine and dairy manures respectively. DIN and DIP concentrations were significantly different among the three manures on all sampling days. Poultry manure supplied the highest amount of nitrogen and phosphorus, followed by swine and dairy manures. Pond fertilization guidelines based on the nitrogen and phosphorus requirements for algae should consider the available portion and not the total nitrogen and phosphorus contents of manures to calculate fertilizer requirements. Another study was conducted to examine the effects of temperature and repeated manure addition on nutrient release patterns from poultry manure. Different temperatures over a three week period did not have a pronounced impact on DIN and DIP levels. Two phases of DIN build-up were observed, whereas DIP levels showed an increasing pattern throughout the temperature experiment. The overall proportion of the total nitrogen and phosphorus supplied by poultry manure that became available as DIN and DIP for all the experimental units considered together amounted to about 64 and 70% respectively, which is consistent with the earlier study. Repeated manure addition resulted in significantly lower DIN and higher DIP concentrations in the interval following the second manure addition compared to the first interval, although nutrient release patterns appeared to be similar. / Graduation date: 1993

Population escalation in the developing world has been associated with increased poverty, food insecurity and environmental degradation. The situation in Rwanda, with 2.82% annual population increase is no exception. The objective of the present study was to investigate an innovative integrated system of sustainable production suitable for resource-poor rural farmers, the Integrated Rabbit–Fish–Rice (IRFR) system. The study was targeted towards contributing to Rwanda government’s goals of eradicating extreme poverty and hunger, enhancing food security as well as abating environmental degradation. Three experiments, were carried out between 2008 and 2010, and designed to fertilise pond water with rabbit droppings and boost phytoplankton production. We also used results from our previous study, conducted in 2005 in the same ponds and under similar experimental conditions, especially rabbit and fish species and age, fishpond dimensions, as well as the fertilisation mode. The fishpond effluent was re-used to irrigate rice fields rather than being discharged into the environment. This study advocated the potential adaptation of rabbits to wetland conditions and the role of rabbit droppings as organic fertilisers in providing a better environment for fish production. On-farm resources, including rabbit droppings, were the main source of nutrients in the system. The analysis of nutrient flow revealed that 27% N and 79% P of the total nitrogen and phosphorus in fertilizing input in fishponds were supplied by rabbit droppings only. Nile tilapia Oreochromis niloticus were able to recover 18.5–37.6% N and 16.9–34.3% P of the total nitrogen and phosphorus inputs, the rest being accumulated in the pond water and the sediment, making them useful for soil fertilisation. The re-use of nutrient-rich effluent in rice irrigation increased rice production, allowing a successful complete substitution of inorganic fertilisers. The irrigation also reduced environmental pollution as the water seeping through rice field was 31.8 and 83.3% less concentrated in total phosphorus and nitrite pollutants, respectively, than was the pond water. Economically, the IRFR generated up to 597% net return over that of the rice inorganically fertilised, thereby substantiating the sustainability of the system. Overall, it is concluded that the IRFR system works well, is readily applicable, and capable of high, diversified, and sustainable production on limited land. As such, the study demonstrates the potentialities of the IRFR system to contribute successfully to poverty reduction, and the enhancement of food security in rural areas. The system promises economic returns and is environmental friendly. The research recommends the optimal range of rabbit density, that is, 800–1200 rabbits per hectare of pond, and the best fish stocking density, that is, 3 fish.mˉ², for a sustainable IRFR culture system. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.