Sub-Saharan Africa is at crossroads. With a rapidly growing population of 1.2 billion and changing climates, the continent faces major development challenges, including food insecurity, climate change, resource degradation, poverty, gender inequality, and social exclusion. While there are multiple competing narratives promoted in the high-input, industrialised world to address climate change and the resilience of agricultural systems (e.g., regenerative agriculture, agroecology), there is an ongoing debate and genuine questions about the appropriateness of these approaches to small-scale farmers in SSA. African agricultural systems are unique, characterised by low productivity, nutrient mining, land degradation, hoe culture, and fragmented and diversified small farms. Though environmental pollution and over-dependence on fossil fuel-powered mechanisation are rarely topping the priority list, climate change is becoming a major concern. The top-down narratives from environment-concerned communities lack the tools to address the most pressing and immediate challenge of local communities in Sub-Saharan Africa, namely (i) intensification by increased crop productivity per unit of inputs, (ii) increased access to rural energy forcing farmers to use available biomass for cooking instead of soil regeneration; (iii) the intent of no use or reduced mineral fertilisers, in a system marred by nutrient mining over centuries; and (iv) failure to address recurrent drought through integrated soil water management interventions. To address these specific challenges, we present context-specific, outcome-oriented farming solutions as a viable and appropriate strategy called ‘sustainable farming’. We argue that the nature-based narratives will remain to be important but will be better adopted if they respond to local demands and context-specific challenges of small-scale farmers. By means of three successful land restoration programmes in East Africa, we present eight outcomes that should be addressed to ensure sustainable farming of small holdings and reduce the risk of climate change. For these innovations to be adopted at scale, we proposed to put in place incentive mechanisms and functional last-mile delivery systems.

Improving fertilizer use efficiency has remained a challenge, particularly for small-scale farming in undulating ‘abnormal’ landscapes of East Africa. Milne's 1930s concept on ‘Catena’ was considered as a breakthrough in understanding soil variability and its implication on productivity in East African highlands. However, there is limited information on how the ‘Catena’ features could be used for fine tuning fertilizer recommendations. We initiated multiple on-farm replicated experiments in three wheat-growing districts (Endamohoni, Lemo and Worreilu) in the Ethiopian highlands in 2014, 2015 and 2016 to assess landscape positions affecting crop-nutrient responses, identify yield limiting nutrients across the ‘Catena’ (N, P, K, S and Zn) and quantify effects of landscape positions on resources use efficiency. We clustered farmlands across the ‘Catena’ (Hillslopes, Midslopes and Footslopes) based on land scape positions in the respective locations. Wheat yield was more strongly and significantly affected by landscape positions (P < 0.001) than by nutrient sources or rates. The crop response to fertilizers was 50 to 300% higher in foot slopes than in hillslopes, depending on locations and inputs levels. With increasing slope, there was a decrease in a crop fertilizer response due to a significant decrease in soil organic carbon, clay content and soil water content, with r² of 0.95, 0.86 and 0.96, respectively. The difference in the crop response between landscape positions was significantly higher (P < 0.05) with higher rates of nutrient applications (>N92 P46) while differences between landscape positions diminish at lower rates. Yield benefits due to application of K was significant only in the dry years (P < 0.05), while there was hardly any yield benefit from the application of zinc and sulfur. The crop nitrogen recovery fraction and crop water productivity decreased with an increasing slope regardless of nutrient combinations. The results indicated that the landscape position could be considered as a proxy indicator for targeted fertilizer application, particularly in farms with undulating topographic features. Hillslopes are better served by the application of organic fertilizers along with conservation measures as applying higher rates of mineral fertilizer in hillslopes would rather increase the risk of downstream nutrient movement.

Land degradation and the associated soil acidity are critical challenge for crop production in Ethiopian highlands. Since liming is expensive, farmers have developed an alternative agroforestry system by integrating Acacia decurrens into their landscapes. The expansion rate of this system was assessed over the last three decades. The effects of the agroforestry system and charcoal-making kiln sites on soil properties were investigated for over five years compared to the adjacent croplands. Soil samples were collected from A. decurrens plantations, kiln sites, and adjacent croplands at 0–15 and 15–30 cm soil depths. In the last 30 years, the plantation and croplands increased by 8% and 17.5%, respectively, compared to the land-use system in 1993, mainly at the expense of grassland and abandoned land. The main incentive for expansion of A. decurrens plantations was farmers’ income generated from charcoal making. This intervention also improved soil properties with a significantly positive effect on soil pH, soil organic carbon (SOC), cation exchange capacity (CEC), and available Bray phosphorus (Bray-P) compared to the adjacent croplands. Results revealed that the SOC content in year 2 increased significantly (1.3–1.7 times) under A. decurrens plantation compared to adjacent crop fields. Moreover, soil pH increased by one unit on charcoal-making fields, which was equivalent to application of 4–5 t lime ha⁻¹, while SOC increased by ~ 10% on kiln sites compared to the control. Charcoal making kiln spots increased available soil phosphorus by 112% compared to the adjacent non-kiln sites. The Bray- P was strongly and significantly (P < 0.05) correlated (r = 0.75) with soil pH. We conclude that integrating A. decurrens-based agroforestry practices would improve livelihoods by restoring degraded lands, improving income generation and carbon sequestration.

Summary: Grain sorghum [Sorghum bicolor (L.) Moench] is the major cereal crop used as staple crop in the arid and semi-arid regions of Ethiopia. Low sorghum yields are attributed to soil, climate and topographic factors. We investigated sorghum yield response to factorial combination of nitrogen and phosphorous (NP) as well as potassium (K), sulphur (S) and zinc (Zn), and how the position of farmers’ fields belonging to different landscape positions (i.e., upslope, mid-slope, and foot slope) could explain fertilizer response and yield variability. The analysis in this study made use of dataset from two sets of on-farm experiments where trials were set at two farmers’ fields for NPKS and three farmers’ fields for NPZn experiments in each landscape position. The experiments were implemented at two sorghum-growing locations (i.e., Hayk and Sirinka) in parts of the north-eastern Amhara region in Ethiopia. Sorghum yield response to fertilizer application was strongly linked to the spatial variation along landscape positions and varied over locations. Fertilizer response was significantly higher at foot slopes compared to mid-slopes and upslope positions, where fields at foot slopes exhibited relatively homogeneous responses. Application of combined nitrogen (N) and phosphorus (P) fertilizers, landscape position and the interaction of fertilizer application and landscape positions strongly affected sorghum yield. There was a linear and significant increase in sorghum yield with the increase in the NP rates. The combined application of NP with different levels of KS as well as NP with Zn fertilizer rates did not result in significant yield difference. The results indicated that local factors were much more influential when accounting for the heterogeneity in sorghum yield response to fertilizer. This further acknowledges the importance of a landscape-based fertilizer management approach to respond yield potential variability related with the farmers’ fields and landscape environment. Further investigation is needed to develop homogeneous fertilizer response units based on spatial variability of soil and topographic attributes along the landscape.

SUMMARY: In the East African highlands, crop yields tend to increase with proximity of the farm plots to homesteads. Farmers identified soil erosion as the most detrimental cause of low crop yield in the outfields followed by soil compaction due to livestock trampling. The main objective of this study was to determine whether zai pits (i.e. small water harvesting pits) developed for dryland regions of the Sahel could increase crop yield and water productivity of degraded outfields in high rainfall areas, where mean annual rainfall exceeds 1300 mm but soil water infiltration is reduced by slope, low soil organic matter and hardpans. The pits were enlarged to resist strong runoff flows. The research was conducted over three years from 2004 to 2006. Potatoes and beans were used as test crops. Overall, compared to control plots, the zai pits, in combination with nitrogen (N) inputs, increased potato yields from 500% to 2000% (p ≤ 0.001). The pits contributed more to increased crop yield than N inputs. Similarly, bean yields from the zai pits were up to 250% higher. Crop water productivity was 300–700% higher with zai pits than with control plots. The income of farmers who used zai pits was up to 20-fold higher than the labour costs required to prepare them. Contrary to conventional wisdom, this study reveals that the major constraint of the outfields is not nutrient deficiency per se rather low soil water holding capacity, which hinders crop growth and efficient utilization of available nutrients.

Micronutrient deficiencies (MNDs), also known as hidden hunger, affect more than a quarter of the global population. Agronomic biofortification helps to increase the concentration of a target mineral in food crops and improve human mineral dietary intake. It is a means of providing nutrient-dense foods to a larger population, especially among rural resource-poor settings, providing that they have access to mineral fertilizers. However, the feasibility of agronomic biofortification in combating hidden hunger depends on several factors in addition to fertilizer access, including crop type, genotype, climate, soils, and soil mineral interactions. Consideration of its effectiveness in increasing human mineral intake to the daily requirements and the improvement of human health and the cost-effectiveness of the program is also important. In this paper, we review the available literature regarding the potential effectiveness and challenges of agronomic biofortification to improve crop micronutrient concentrations and reduce hidden hunger.