Oyster mushroom cultivation on straw: Aspects of productivity, sustainability and adaptability to the case of Uganda[Anbau von Austernpilzen auf Stroh: Aspekte der Produktivität, Nachhaltigkeit und Anwendbarkeit im Falle Ugandas]

The research presented in this PhD thesis examines various aspects of oyster mushroom cultivation and food security, focusing on production, sustainability and adaptation in the case of Uganda. Due to population growth, decreasing crop land availability, depletion of agricultural resources and climate change, landless food production and circular agricultural systems could play a more important role in the future. It is particularly important to develop sustainable production techniques adapted to the context of sub- Saharan Africa, where the challenges are the greatest. Oyster mushrooms are protein-rich, high-yielding, can by cultivated on a wide range of crop residues and are the most commonly cultivated mushroom in Uganda and many other African countries. This makes them an important subject to study in the context of food security. A review of the scientific literature on mushroom cultivation in the context of recycling discusses several pathways in which mushroom cultivation can contribute to the agricultural system as a whole, in addition to the primary objective of producing mushrooms. The use of spent mushroom substrate for vermicomposting to produce high quality compost and earthworms that can be used as animal feed may be the most promising circular model. However, there are many other options, such as using the mushrooms themselves as animal feed or producing several mushroom species in succession on the same substrate. Since sustainable mushroom production requires an integration with crop and livestock production within a circular system, it is an important question which substrates to use for cultivation. The use of nutrient- poor straw from cereals and legumes for oyster mushroom cultivation is a good option, as these substrates only have very limited value as animal feed. The productivity of four different types of straw was determined experimentally. Maize and soy straw were particularly productive, yielding 9.2 and 8.6 g of dry mushrooms per 100 g of dry substrate. Faba bean straw was significantly less productive, with only 6.6 % of the substrate being converted into mushrooms. However, faba bean straw, which had the highest nitrogen content of the four straw types that were compared, also produced mushrooms with a higher protein content. Wheat straw, on the other hand, was found to be an inferior substrate, yielding only 3.8 g of dry mushrooms per 100 g of dry substrate. Approximately 60 - 80 % of the dry matter, carbon and nitrogen is retained in the spent mushroom substrate after cultivation and between 3.5 kg (on wheat straw) and 2.6 kg (on soy straw) of carbon is emitted per kg of mushroom produced. Despite promising prospects, some aspects of current mushroom production are not sustainable. In particular, the pasteurization or sterilization of mushroom substrates uses a lot of energy and water. In an experimental comparison of four different methods, hot air pasteurization emerges as the most sustainable option. However, it was also found that sterilization can significantly increase oyster mushroom yields compared to pasteurization. The first harvest was up to 50 % higher when the substrate was autoclaved, while no significant difference could be found between the different pasteurization methods. Adapting the use of sustainably sourced substrates and of resource-efficient pasteurization or sterilization methods to Uganda, was found to be challenging but ultimately have great potential for improving local food security. In a case-study, including field work, key-informant interviews and a mushroom cultivation experiment, maize stover was found to be an underutilized resource. 13 % more food and 33 % more protein could be produced on the same land if maize stover was used for mushroom cultivation instead of being burned, which is currently a common practice in Uganda. The main challenges to realizing this potential are infrastructural barriers for collecting and preparing maize straw for mushroom cultivation and for distributing cheap, high-quality mushroom spawn. It is also important to enable Ugandan mushroom farmers to use more sustainable pasteurization practices if mushroom production is to be promoted in the country. Given the great potential of mushroom production to increase food security and improve the 59 sustainability of the agricultural production, more resources should be devoted to researching mushroom cultivation in circular food systems and developing solutions that are applicable to the sub-Saharan African context.