Lack of nitrogen limits food production in poor countries while excessive nitrogen use in industrial countries has led to transgression of the planetary boundary. However, the potential of spatial redistribution of nitrogen input for food security when returning to the safe boundary has not been quantified in a robust manner. Using an emulator of a global gridded crop model ensemble, we found that redistribution of current nitrogen input to major cereals among countries can double production in the most food-insecure countries, while increasing global production of these crops by 12% with no notable regional loss or reducing the nitrogen input to the current production by one-third. Redistribution of the input within the boundary increased production by 6–8% compared to the current relative distribution, increasing production in the food-insecure countries by two-thirds. Our findings provide georeferenced guidelines for redistributing nitrogen use to enhance food security while safeguarding the planet.

The organic matter stored in soils is a major carbon pool with fundamental importance for the global atmospheric carbon balance. Its decomposition contributes not only to the emission of greenhouse gases into the atmosphere but also to the release of minerals that serve as nutrients for plants growing in these soils. SOC is an indicator of soil fertility, reflecting the influences of agricultural practices on this property. Using crop models, the amount of soil organic carbon (SOC) can be simulated under the assumption of different climate scenarios and different agricultural practices. The conventional agricultural practice in Czechia includes short crop rotations of mainly cereals and oilseed rape, mineral fertilisation and removal of crop residues for technical and energy use. However, the conventional approach is often associated with soil degradation and constant depletion of soil carbon stocks. Based on the standard crop rotation method, we compared the conventional practice (CR1) to an alternative practice (CR2), in which more effort is made towards stabilising soil carbon stocks by including cover crops in the rotation, organic fertilizers and leaving crop residues in the field. We used an ensemble of crop models (APSIM, DAISY, DSSAT, HERMES, and MONICA) to assess the carbon loss from two typical agricultural soils (Chernozem and Cambisol) at three locations in Czechia under current and future climate conditions (RCP 8.5, as represented by five global climate models). The ensemble simulations revealed that using CR2 could lead to an average increase in the SOC content by 15.427 kg/ha for Chernozem and 12.624 kg/ha for Cambisol until 2080. With the use of CR1 the SOC values on average decreased by 34.462 kg/ha for Chernozem and 24.096 kg/ * Corresponding authors at: Global Change Research Institute Academy of Sciences of the Czech Republic, Belidla 986/4b, 2 ha for Cambisol until 2080. The 1990 value was taken as the SOC reference level. Furthermore, both the increase (CR2) and decrease (CR1) amounts SOC stabilised after 2050. As such, even at the cost of high levels of nitrogen fertilisation and the associated risk of nitrogen leaching (CR2), the additional carbon that can be stored in soils is limited. The differences due to the different climate models are negligible in the case of CR1, while in the case of CR2, the different climate scenarios (baseline vs. future) yielded different SOC equilibrium levels, with a lower level (by 4.400 kg/ha on average) under the RCP 8.5 scenario for both soils. The results showed that carbon can be sequestered by increasing organic inputs. The crop models predicted that CR2 could lead to a higher SOC content, which occurs at the cost of high manure application levels and increased risk of nitrogen leaching.

To address the rising global food demand in a changing climate, yield gaps (Y G), the difference between potential yields under irrigated (Y P) or rainfed conditions (Y WL) and actual farmers' yields (Y a), must be significantly narrowed whilst raising potential yields. Here, we examined the likely impacts of climate change (including changes in climatic variability) and improvements in agricultural technologies on crop yields and yield gaps. Eight rigorously tested crop simulation models were calibrated for wheat and maize and run at 10 different sites around the world. Simulations were performed to estimate Y P , Y WL and yields achievable under three locally defined technology packages: TP 0 represents average farmer's practice, while TP 1 and TP 2 are increasingly advanced technologies. Simulations were run for the baseline (1981-2010) and twelve future climate scenarios for 2050, representing changes in the means of climate variables and in the variability of daily temperature and dry/wet spell durations. Our basic hypotheses were that (H1) mean climate changes combined with increased weather variability lead to more negative yield impacts than mean climate changes alone, and (H2) advanced technologies would serve as effective adaptations under future climatic conditions. We found that crop responses were dependent on site characteristics, climate scenarios and adopted technologies. Our findings did not support H1. As for H2, the improved technology packages increased wheat and maize yields at all sites, but yield gap reduction varied substantially among sites. Future studies should consider a broader range of climate scenarios and methods for analysing potential shifts in climate variability. Moreover, it is recommended to co-create and evaluate climate zone-specific climate-smart crop production technologies in interaction with a wide range of local stakeholders. Abbreviations Y P = Potential yield as simulated for irrigated conditions (kg ha −1) Y WL = Water-limited potential yield as simulated for rain-fed conditions (kg ha −1) Y a = Actual farmers' yield under current average farm-ers' management practices (kg ha −1) Y a-future = Future actual farmers' yield under assumed average farmers' practices in 2050 (kg ha −1) Y G = Yield gap (Y P-Y a or Y WL-Y a , in kg ha −1, 100*(Y P-Y a)/Y P or 100*(Y WL-Y a)/Y WL , in%) RY = Relative yield(100*(Y a /Y WL) or 100*(Y a /Y P), in%) TP 0 = Current technology (current average farmer's practice regarding cultivar choice, sowing date, water and nutrient management) TP 1 = Conservative change in technology (cultivar, sowing date, water and nutrient management) TP 2 = Advanced, eco-efficient technology improvement (cultivar, sowing date, water and nutrient management)

The sustainability of southern Africa’s natural and managed marine and terrestrial ecosystems is threatened by overuse, mismanagement, population pressures, degradation, and climate change. Counteracting unsustainable development requires a deep understanding of earth system processes and how these are affected by ongoing and anticipated global changes. This information must be translated into practical policy and management interventions. Ten years ago, the Federal Ministry of Education and Research initiated the “Science Partnerships for the Assessment of Adaptation to Complex Earth System Processes”, SPACES for short, together with organisations in southern Africa. Cooperation between my Ministry, the South African Department of Science and Innovation, the Namibian Ministry for Higher Education, Technology and Innovation, and the Namibian National Commission on Research, Science and Technology provides the basis. The aim is to support joint projects conducted by German research institutions with partner institutions in South Africa, Namibia, and the neighbouring countries to improve our understanding of the region’s sensitive ecosystems. The SPACES programme pools capacities and provides all those involved with access to a unique research infrastructure and key field sites. As a result, major findings are now available about climate change and extreme weather processes as well as social-ecological aspects of food production that are vital for the region given the expected increase in heat waves, flooding, and droughts. The knowledge gained provides the basis for innovations, new technologies, and recommendations for action to promote the sustainable use of agricultural land as well as of coasts and seas. At the same time, it provides good orientation for political decision-making and transformation processes. The available results have already been included in publications of the IPCC and IPBES. This highlights their importance for sociopolitical debates and our actions as we move along the path set out by the Agenda 2030. This book presents the latest findings for managing the valuable and diverse ecosystems in the temperate, subtropical, and tropical regions of southern Africa.