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Edible mushrooms are cultivated mainly on ligno-cellulosic plant materials, thereby turning agricultural wastes to high-quality products. In this review, several ways in which mushroom cultivation could help in the transition towards a circular agricultural economy are discussed, including food, feed, and compost production. The production processes of different mushroom species are also described and an overview of the global mushroom market and its history are given. Resource use efficiency could be maximized by using spent mushroom substrate as feed for invertebrates, such as insects or earthworms, which produce high-quality compost and can serve as food or feed for other livestock. In the context of an increasing world population, as well as limited resources and agricultural land, mushroom cultivation could fulfill the need for protein-rich food and for the recycling of nutrient-poor agricultural wastes.

On smallholder farms in Ethiopia, livestock manure and organic residues are traditionally removed from fields for construction, feed, and fuel purposes, while the remainder stays in the field as feed or fertilizer. Burning and removing organic matter without replacing it leads to valuable losses of on-farm nutrients and soil carbon, which could otherwise be used to fertilize crops. Instead, resources need to be used efficiently by reducing and recycling organic residues and forming a closed production system. Competition between applications can be eliminated by bio-methanation using a biodigester. There, organic residues are transformed to biogas utilized for light and cooking and bioslurry, a nutritious organic fertilizer and source of organic matter. Through capturing nutrients in agricultural by-products, nutrients become available to the food system again. Literature review has been supplemented with empirical evidence from a study carried out in the central Ethiopian Highlands on 47 smallholder farms, to provide a baseline for further improvements on the management of biogas technology. The study identifies a series of inadequate handling practices and thus a significant potential to optimize the farming system around a biodigester. It is recommended to include forage legumes in the farm system to enhance on-farm available nutrients that can be recycled through a biodigester. It is further necessary to involve the private sector in biodigester programs, to improve local availability of materials, which are suitable to the local culture and traditions. Space for knowledge exchange between farmers and advisors like demonstration farms can further improve bioslurry management. Although challenges remain, the integration of a biodigester should be encouraged as it fulfills the production of energy and a nutritious and economic fertilizer without additional resources, resulting in a win-win situation for the farmer.

Four hundred fifty-eight meter square is the available cropland per person throughout Africa, if the population will increase 4 to 5 times towards 4.3 to 5.9 billion people in 2100, the maximum estimation of the UN 2019 (95% confidence interval). This space is not enough for food sovereignty, if the low African yields remain. Even with the global average yields, nearly 3 times higher than African yields, will not allow food sovereignty. Hunger, wars, diseases, and mass migration can be the consequences already long time before 2100. Nevertheless, food sovereignty is possible, but not in the way as it is done up to today by governments and development projects. In the future, intensification of (yields) and/or expansion (grassland, forest: LULUCF) of agriculture will not be able to produce enough, nutritious, and affordable food for everyone. But clever combining of land-based and landless food production can be a solution for a local, sustainable, and circular food security. Maize and soybeans are best for WFP minimum diets and have the best yields. Using insects and earthworms as protein source can deliver enough and nutritious protein, and local photoreactors can produce oil/and/or starch for food energy. Later can be large industrial and very small household scaled. This “out-of-the-box” system approach needs research and development. Every good research needs good questions and a concept with some simple calculations to assess the strengths, weaknesses, opportunities, and threats. Socio-economic aspects are often not considered enough in technical focused and far ahead R&D.

For feeding the world in 2100, the global agriculture, the entire food chain, as well as the behavior of all consumers must be change fundamentally. Essential resources needed to intensify agriculture and use barren land, such as phosphorus, water, and fossil fuels, are becoming increasingly scarce and expensive. An ecological form of agriculture that uses these resources more responsibly requires more land for the same yields. Therefore, new concepts for food and feed production have to be developed, in which nutrients are recycled beyond these areas. A possible starting point could be bioreactors, since these are enormously efficient and enable resource-efficient land use. Wastewater treatment as a means of nutrient recycling will be one of the most important tasks in the future. Hereby, not only the heterotrophic bioreactors currently used for this purpose but also autotrophic photobioreactors show great potential, especially if these two reactor types would be combined. Because of the ability to use inorganic nitrogen and phosphorus for their growth as well as the ability to produce a wide range of metabolites, microalgae offer an integrated approach. This review provides an overview of the potential of microalgae as components of a sustainable, circular agricultural system for feed and food production.

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Even optimistic assumptions about population growth, agricultural productivity, and potentially available cropland produce a grim image for the future food security and sovereignty of many developing countries, in particular in sub-Saharan Africa. Here, we review literature and datasets on the current and future state of food security, with focus on Africa, and propose a plan of ten interconnected actions to create sustainable, circular, and local food systems to feed a global population between 11.2 and 16.6 billion people in 2100. In particular, we focus on “action number 10”: landless food systems in combination with land-based food production, using modern “organic agricultural strategies.” The concept shall be applicable to the needs and conditions in low-income countries with high population densities and small-scale farming systems, as expected in sub-Saharan Africa in 2100. We designed the concept “LandLessFood” with research recommendations for a circular bioreactor-based system of “calorie food and feed.” Our aim is to “replace one hectare of cropland with one square meter of bioreactor space.” Released cropland can and has to be used for “quality food” production to have enough, healthy, and affordable food for everyone on the earth in the year 2100.

This special issue presents the outcomes from “ Designing sustainable and circular agricultural systems for the year 2100 ,” the joint scientific workshop of ISOFAR, the Thünen-Institute, and INRA-Morocco, which was held from November 14 to 16, 2019 in Marrakesh, Morocco. Nineteen scientists from a broad array of background and nationalities came together with the understanding that food security globally is at risk, especially in the post-2050 timeframe. Current concepts, strategies, measures, and scientific efforts carried out by governments, NGOs, businesses, and societies do not deliver satisfying solutions for how to sustainably produce enough healthy and affordable food to support the global population. With the economic and social impact of the Covid-19 pandemic in 2020, it became even more evident that food security is a challenge. This workshop took an innovative approach to addressing the challenges of future agriculture by considering sustainable, circular agricultural systems. Participants presented research results on algae-based food, edible insects, mushrooms, novel concepts for nutrient management, bioreactor-based farming, sustainable food culture, as well as sensor- and remote-controlled automatic food production. This special issue presents the papers contributed to the workshop and the results of the discussions.

Sustainable rangeland management is crucial for conservation and improvement of global grassland ecosystems, livestock performance and grassland-linked livelihoods. This applies in particular for Sub-Saharan African countries like Namibia with its rangeland-based low external input livestock husbandry. In the local savannas, productivity and resource distribution is spatially heterogeneous and temporally variable, which calls for adaptive and responsive grazing strategies to meet the needs of livestock and vegetation. The adjustment of stocking rate (SR; kilogramme livestock per hectare per year) and stocking density (SD; kilogramme livestock per hectare during a specific grazing event) is considered as a key success factor but very different rates and densities have been recommended in the past by practitioners, scientific evidence is lacking. On an Organic Namibian beef cattle and sheep farm were these recommendations assessed in order to investigate the responses of savanna rangelands to varying grazing intensities. Since 2014, forage biomass production and composition under three different grazing regimes have been assessed: (1) the routine management (here Holistic Management) as control and in comparison to this (2) an increased SR or (3) increased SD. Destructive biomass sampling was done each May in 2014, 2015, 2016 and 2017, respectively. The results showed that the increased SR or SD can be beneficial for average fodder production, but not significantly. However, the negative standing dead biomass accumulation was significantly reduced.