Purpose: This study explored the potential of aluminium water treatment residuals (Al-WTR), a by-product of drinking water purification, to improve soil quality and maize productivity on a degraded sandy soil. Methods: A field experiment was conducted over two cropping seasons (2019/20 and 2020/21), with treatments including sole applications of cattle manure (CM), maize stover (MS), Al-WTR, their co-amendments (Al-WTR + CM and Al-WTR + MS), NPK fertiliser, and an unamended control. Soil samples collected during the 2020/21 season (at 0–10 and 10–20 cm depths, and 3 and 6 weeks after planting) were analysed for soil organic carbon (SOC), total nitrogen (TN), microbial biomass carbon (MBC) and nitrogen (MBN), and basal respiration. Maize grain and biomass yields were recorded at physiological maturity for both seasons. Results: Co-amended treatments significantly increased SOC (> 4.90 g kg⁻¹) and TN (> 0.60 g kg⁻¹), compared to single amendments (< 4.80 g kg⁻¹ SOC; 0.50 g kg⁻¹ TN). At 6 WAP and 0–10 cm depth, Al-WTR + CM recorded the highest MBC (190 ± 1.14 mg C kg⁻¹) and MBN (35.80 ± 0.51 mg N kg⁻¹), while the control recorded the lowest (120 ± 1.58 mg C kg⁻¹; 18.72 ± 0.35 mg N kg⁻¹). Basal respiration also increased with co-amendments. Al-WTR + CM yielded 5.61 ± 0.05 t ha⁻¹ maize grain (2020/21), while the control yielded below 1 t ha⁻¹ in both seasons. Conclusion: The findings demonstrate that Al-WTR co-amendments can effectively restore soil function and support resilient maize production in degraded agroecosystems.

Abstract Novel climate conditions are posing a serious threat to humanity and ecological systems, presenting and aggravating social injustices at different levels. African agriculture-based livelihood systems will be invariably the most affected because of their reliance on climate-sensitive agriculture and limited adaptive capacity due to low economic development linked primarily to historical contingency. Just transition pathways for Africa’s agriculture are urgently required for sustainable production systems that enhance food security and poverty reduction, while optimising mitigation co-benefits. We critically reviewed and synthesised literature from relevant scientific reports and peer-reviewed articles to develop a framework for just transition pathways for Africa’s agriculture towards low emission and climate resilient development under a 1.5°C global warming. We first characterise current and future climate hazards and assess climate risks underpinning African agriculture-based livelihoods. Our results demonstrated that a 1.5°C global warming will be approached by 2040 in all five subregions of Africa, even under low emission scenarios. This is despite Africa emitting <4% concentration of greenhouse gas emissions in the atmosphere. The African agriculture-based livelihood systems have experienced considerable losses and damages from climate change and this will worsen with increasing intensity of climate hazards. Neither the existing or planned incremental adaptation mechanisms nor the anticipated benefits of mitigatory measures are sufficiently comprehensive to match the pending novel climate conditions. We argue that the just transition pathways for Africa’s agriculture should be anchored on reprogramming of the cropping, livestock and fishery systems for climate-proofing with a specific focus on the following underpinnings: financing the advancement of science, technology and innovation; restoring neglected or underulitised crops and livestock genetic pools; regenerating soil fertility and advancing soil health; restoring degraded land; protecting natural ecosystems and biodiversity; accessing quality education training and information technologies; and developing markets and creating novel distribution and trade opportunities. Such efforts should also focus on mechanising and greening Africa’s agriculture as driven by a deliberate ‘Green Industrial Revolution’ for the new normal induced by climate change. The sustainability of climate change response and a just transition pathway framework for Africa also lies in the corresponding transformation of education systems and research capacities tailored to drive economic development for Africa. In conclusion, the developed just transition framework offers opportunities for social inclusion, equity, building capacity for self-mobilisation and self-organisation of communities for climate action, and investments in the transition pathways for building a climate resilient agriculture towards zero poverty and meaningful contribution towards zero carbon.

Traditional cereal crops are important for food and nutrition security in rural communities of southern Africa, but their productivity is often constrained by low soil water largely linked to low seasonal rainfall and long intra-seasonal dry spells. Planting basins (PB), tied ridges (TR), and conventional ploughing (CP) were evaluated, over two cropping seasons (2020/2021 and 2021/2022), for their effects on sorghum [Sorghum bicolor (L.), Moench], pearl millet [Pennisetum glaucum (L.) R.Br.], and finger millet [Eleusine coracana (L.) Gaertn] productivity on degraded (<0.4% soil organic carbon) and productive (>0.6% soil organic carbon) fields under rainfed conditions in Mbire (<450 mm rainfall year−1) and Mutasa (>800 mm rainfall year−1) districts in Zimbabwe. Field trials were established on degraded and productive field sites in each district, with sorghum, pearl millet, and finger millet either sown as monocrops or intercropped with cowpea. The experiments were laid out in a 2 × 3 × 3 factorial in a randomized complete block design (RCBD). The highest sorghum grain yield response of 2100 kg ha−1 was attained under PB on productive soils. Overall, PB and TR increased sorghum, finger millet, and pearl millet grain yields by 43% to 58% compared with CP. Growing sorghum, finger millet, and pearl millet on productive soils increased grain yields by 64%, 33%, and 43%, respectively, compared with degraded soils. Intercropping sorghum, pearl millet, and finger millet with cowpea increased cereal yields by between 23% and 42% over the sole crops. Rainwater use efficiency averaged 1 kg grain mm−1 on productive fields and 0.4 kg grain mm−1 on degraded fields. PB produced the highest net profit of $US408 on a productive field. Overall, production of sorghum and millets on productive soils gave positive economic returns irrespective of rainwater management option and cropping system. Conversely, 63% of the treatments on degraded soils recorded negative economic returns in both districts. We conclude that in-field rainwater management technologies combined with other agronomic practices like intercropping increase the productivity of sorghum and millets under rainfed conditions. However, degraded soils remain a challenge for the increased productivity of traditional cereal crops.

CONTEXT: Despite recent improvements in living standards, a substantial proportion of farm households in sub-Saharan Africa (SSA) is food insecure, and increasing crop productivity could help address this problem.OBJECTIVE: We estimated the effect of increasing maize yields with mineral fertilizer on household food security and on regional and national maize supply in two East African countries -Uganda and Tanzania.METHODS: We estimated maize yield response to nitrogen (N) fertilization with a machine learning model trained on 15,952 observations of maize responses to fertilizer across SSA. Together with spatial price data, we used this model to quantify the profit-maximizing N fertilizer input for a nationally-representative sample of 4188 agricultural households in the two countries. We computed a food availability indicator for all households.RESULTS AND CONCLUSIONS: The mean profit-maximizing N input was 82 kg/ha in Tanzania, but it was much lower in Uganda (24 kg/ha) mostly because of less favorable prices. The profit-maximizing N input was above the reported N input for 95% of the households in Tanzania and for 43% of the households in Uganda. It was predicted to increase the food availability ratio of food insecure maize growers by 95% in Tanzania, and by 25% in Uganda. The administrative regions where maize supply could increase most were not the same as the regions where the increase in household-level food security was largest. With increased fertilization, food insecure maize growing households (35% in Tanzania and 42% in Uganda) could only contribute about 20% of the overall increase in maize supply, whereas the 20 to 30% food secure households that have a larger area planted with maize could contribute >60%.SIGNIFICANCE: Our study makes two key contributions: i) a substantial increase in national maize supply is more likely to come from already food secure households with relatively large farms, while food insecure households with small farms may nevertheless increase their household-level food security through maize intensification, and ii) high potential areas to increase maize domestic production do not necessarily match with areas where there is immediate scope to improve household-level food security.

IntroductionSoil degradation coupled with poor access to organic nutrient resources remains a major constraint in increased crop productivity in sub-Saharan Africa, thus hindering the continent's efforts in achieving the United Nations' Sustainable Development Goals, particularly goals 1 (end poverty), 2 (zero hunger) and 3 (improve human health). Water treatment residual (WTR), a by-product of clean water treatment, has been identified as an alternative organic nutrient resource for crop production. However, there are some inconsistences in soil phosphorus (P) dynamics following aluminium WTR (Al-WTR) application.Materials & MethodsA laboratory experiment was conducted to evaluate the P sorption of a sandy soil amended with 10% Al-WTR, 10% compost (C) as a quasi-control, 10% C + 10% Al-WTR (10% coamendment) and 5% C + 5% Al-WTR (5% coamendment) under varying levels of pH, particle size and P concentration. We calculated crop P fertilizer requirements under different amendments.ResultsThe results demonstrated that all amendments exceeded the minimum of 0.2 mg P L-1 needed in soil solution at equilibrium to maintain plant growth. However, the maximum P sorption capacity was higher for 10% Al-WTR single amendment, ranging from 770 to 1000 mg P Kg-1, and from 714 to 1000 mg P Kg-1 and 555 to 909 mg P Kg-1 for 10% and 5% coamendments, respectively, across a range of pH and soil particle size fractions. The coamendments showed a reduction in crop P fertilizer requirements by ranges of 30-60% and 60-70% for the 10% and 5% coamendment levels, respectively, across different pH and particle sizes, relative to 10% Al-WTR.ConclusionResults show that the use of 5% coamendment in sandy soils increases P availability sufficiently to improve crop yields. The results provide scope for using Al-WTR coamendments to rebuild soil health in sandy soils in urban agriculture and increase macronutrient provision in crops to support human health.

Developing optimal strategies for nutrient management of soils and crops at a larger scale requires an understanding of nutrient limitations and imbalances. The availability of extensive data (n = 1,781) from 2-yr nutrient omission trials in the most suitable agroecological zone for maize (Zea mays L.) in Nigeria (i.e., the northern Guinea savanna) provides an opportunity to assess nutrient limitations and imbalances using the concept of multi-ratio compositional nutrient diagnosis (CND). We also compared and contrasted the use of linear regression models and bootstrap forest machine learning to predict maize yield based on nutrient concentration in ear leaves. The results showed that 35% of the experimental plots had low yields due to nutrient imbalances (hereafter referred to as low yield imbalanced [LYI]). These experimental plots were dominated by control plots (without any nutrients applied), plots without N fertilization, and plots without P fertilization. Using the control plot as the ultimate indicator of nutrient imbalance, the significantly limiting nutrients in order of decreasing frequency of deficiency were N, P, S, Ca > Cu, and B. Both linear regression and bootstrap forest machine learning models fairly predicted maize grain yield based on nutrient concentration in ear leaves only in the LYI group and when examining all data with an independent validation dataset. These results suggest that nutrient management strategies, especially through the site-specific management approach, should consider S, Ca, Cu, and B in addition to the existing nutrients N, P, and K to improve nutrient balance and maize yield in the study area.

Increasing within-season dry spells in Southern Africa in recent years have generated growing interest in conservation agriculture (CA) to secure crop yields, especially under rainfed systems. This study aimed to evaluate the effects of CA on finger millet’s (Eleusine coracana (L.) Gaertn) growth, yield and water use efficiency on nutrient-depleted sandy soils. Five treatments, namely (conventional tillage (control), conventional tillage + mulch (partial CA1), reduced tillage only (partial CA2), reduced tillage + mulching (partial CA3) and reduced tillage + mulching + intercropping (full CA)) were evaluated over two consecutive cropping seasons (2015/16 and 2016/17) on-farm in the village of Chidora in Hwedza District, southeast Zimbabwe. All mulched treatments had 15–32% more soil water content over the two growing seasons compared to the control. The higher soil water content under the mulched treatments significantly improved finger millet growth and development during both seasons as evidenced by the lower number of days to emergence (3 days less), greater shoot biomass, higher number of productive tillers and higher number of fingers produced. The full CA treatment achieved the best finger millet grain yield of 1.07 and 1.29 t ha−1 during the 2015/16 and 2016/17 seasons, respectively. Full CA, partial CA3 and partial CA1 increased finger millet grain yield by 70%, 14% and 17% during the 2015/16 cropping season compared to the control. During the 2016/17 cropping season, a similar trend in finger millet grain yield was observed. Full CA was also among the most efficient methods in terms of water utilization (WUE), especially during the 2015/16 season. We concluded that CA, particularly when practiced in full, was more effective at offsetting the water limitations imposed by intra-seasonal dry spells on finger millet and significantly improved productivity.

Absence of site-specific nutrient recommendation and high spatial variability of soil fertility are major factors affecting maize response to applied nutrients in Nigeria. In this study, we assessed maize response to applied nutrients and nutrient use efficiency in different management zones (MZs), for designing site-specific nutrient management recommendations for maize in the maize belt of Nigeria. The maize belt in Nigeria was earlier delineated into four MZsMZs (MZ1 to MZ4) based on soil properties. In the current study, data from two different trials, nutrient omission trials ( N = 293) and fertilizer response trial ( N = 705), conducted in the years 2015–2017, were extracted for MZ1 to MZ3; to analyze maize yield responses to application of N, P and K, and secondary and micro-nutrients. Maize yield response to K application was only positive in MZ1. Responses to N and P application were positive for all MZs. However, the magnitude of maize response to P varied between the MZs, indicating a differentiation in the degree to which P is limiting maize production in the study area. Average nitrogen requirement was higher for MZ3 (138 kg ha −1 ), than for MZ2 and MZ1 (121 and 83 kg ha −1 , respectively). Average P requirement was higher for MZ3 (45 kg ha −1 ) than for the other zones. Potassium requirement was 26% and 28% higher in MZ2 and MZ3 compared with MZ1 (∼15 kg ha −1 ). The use of the specific nutrient rates for the MZs may reduce risks and uncertainties in crop production. The delineated MZs of the maize belt of Nigeria that incorporates spatial variability in soil fertility conditions are useful for nutrient management for larger areas.

Despite recent improvements in living standards, a substantial proportion of farm households in sub-Saharan Africa (SSA) is food insecure, and increasing crop productivity could help address this problem. We estimated the effect of increasing maize yields with mineral fertilizer on household food security and on regional and national maize supply in two East African countries - Uganda and Tanzania. We trained a machine learning model with data from 15,526 maize fertilizer trials across sub-Saharan Africa. Together with spatial price data, we used this model to quantify the profit-maximizing N fertilizer input for a nationally-representative sample of 4188 agricultural households in the two countries. The mean profit-maximizing N input was 82 kg ha -1 in Tanzania, but it was much lower in Uganda (24 kg ha -1 ) mostly because of less favorable prices. The profit-maximizing N input was above the reported N input for 95% of the households in Tanzania and for 43% of the households in Uganda and could increase the food availability ratio of food insecure maize growers by 95% in Tanzania, and by 25% in Uganda. Administrative regions where maize supply could increase most were not the same as the administrative regions where there was more opportunity to improve household-level food security. Food insecure maize growing households (35% in Tanzania and 42% in Uganda) could contribute to less than 22% of the overall increase in maize supply, whereas the 20 to 30% food secure households with more area planted with maize contributed more than 60%. These results suggest that substantial increases in national maize supply are more likely to come from already food secure households with larger farms, while food insecure households with smaller farms may increase their household-level food security through maize intensification.

Physiological use efficiency (PUE), recovery fraction of applied nutrients and indigenous soil nutrient supply form the basis of site-specific fertilizer recommendations. To derive these parameters, and understand their variability, as well as yield responses and fertilizer use profitability, nutrient omission trials (NOTs) were conducted in farmers' fields across different agro-ecologies in Bako (n = 37), Central Rift Valley (CRV) (n = 66) and Jimma (n = 44) regions of Ethiopia in the main crop growing seasons of 2015 and 2016. The treatments used in the NOTs were control, PK, NK, NP, NPK and NPKSM, where SM refers to secondary and micro nutrients, and applied levels of N, P and K, were 120, 40 and 40 kg /ha, respectively. The results showed that the average yields of the control treatment were 4.5, 3.1 and 2.9 t/ha in Bako, CRV and Jimma, whereas the average yields for the NPK treatment were 8.3, 4.9 and 7.9 t/ha in the respective regions. Nitrogen was limiting grain yield in all the three regions, whereas P limited yield only in CRV and Jimma. The average N agronomic efficiencies in Bako, CRV and Jimma were 25.7, 13.3 and 35.5 kg grain kg(-1) of applied N, respectively, under NPK fertilizer use. With the levels of fertilizer used in the NOTs, NK, NP and NPK treatments were profitable in Bako and Jimma, whereas PK was not. None of the fertilizer treatments were profitable in CRV. Soils in Bako and Jimma supplied more N and K but less P than the soils in CRV. The PUE at maximum accumulation, median and maximum dilution of N were 27, 54 and 80 kg grain kg(-1) N, while for P, the values were estimated to be 194, 350 and 505 kg grain kg(-1) P, and for K they were 16, 52 and 87 kg grain kg(-1) K. The estimated average N, P and K recovery fractions were 0.29, 0.05 and 0.06, respectively, in Bako, 0.22, 0.10 and 0.15 in CRV, and 0.38, 0.10 and 0.01 in Jimma. While these average parameter values are relevant, in particular agronomic use efficiencies and recovery fractions showed large variability and, moreover, averages were lower than what is deemed feasible with good agronomy. We discuss the variability in the derived parameters, the relation with yield levels, soil nutrient supply and rainfall, and conclude that caution is needed when deriving fertilizer recommendations from parameters obtained in on-farm experiments. Using single estimated average values is not sufficient: variability in these parameters and sub-optimum values need to be explained first, and derived insight should be used when developing site-specific fertilizer recommendations.

Soil degradation, which is linked to poor nutrient management, remains a major constraint to sustained crop production in smallholder urban agriculture (UA) in sub-Saharan Africa (SSA). While organic nutrient resources are often used in UA to complement mineral fertilizers in soil fertility management, they are usually scarce and of poor quality to provide optimum nutrients for crop uptake. Alternative soil nutrient management options are required. This study, therefore, evaluates the short-term benefits of applying an aluminium-based water treatment residual (Al-WTR), in combination with compost and inorganic P fertilizer, on soil chemical properties, and maize (Zea mays L.) productivity and nutrient uptake. An eight-week greenhouse experiment was established with 12 treatments consisting of soil, Al-WTR and compost (with or without P fertilizer). The co-amendment (10% Al-WTR + 10% compost) produced maize shoot biomass of 3.92 ± 0.16 g at 5 weeks after emergence, significantly (p < 0.05) out-yielding the unamended control which yielded 1.33 ± 0.17 g. The addition of P fertilizer to the co-amendment further increased maize shoot yield by about twofold (7.23 ± 0.07 g). The co-amendment (10% Al-WTR + 10% C) with P increased maize uptake of zinc (Zn), copper (Cu) and manganese (Mn), compared with 10% C + P. Overall, the results demonstrate that combining Al-WTR, compost and P fertilizer increases maize productivity and micronutrient uptake in comparison with single amendments of compost and fertilizer. The enhanced micronutrient uptake can potentially improve maize grain quality, and subsequently human nutrition for the urban population of SSA, partly addressing the UN’s Sustainable Development Goal number 3 of improving diets.

A synthesis of available agronomic datasets and peer-reviewed scientific literature was conducted to: (1) assess the status of micronutrients in sub-Saharan Africa (SSA) arable soils, (2) improve the understanding of the relations between soil quality/management and crop nutritional quality and (3) evaluate the potential profitability of application of secondary and micronutrients to key food crops in SSA, namely maize (Zea mays L.), beans (Phaseolus spp. and Vicia faba L.), wheat (Triticum aestivum L.) and rice (Oryza sativa L.). We found that there is evidence of widespread but varying micronutrient deficiencies in SSA arable soils and that simultaneous deficiencies of multiple elements (co-occurrence) are prevalent. Zinc (Zn) predominates the list of micronutrients that are deficient in SSA arable soils. Boron (B), iron (Fe), molybdenum (Mo) and copper (Cu) deficiencies are also common. Micronutrient fertilization/agronomic biofortification increases micronutrient concentrations in edible plant organs, and it was profitable to apply fertilizers containing micronutrient elements in 60–80% of the cases. However, both the plant nutritional quality and profit had large variations. Possible causes of this variation may be differences in crop species and cultivars, fertilizer type and application methods, climate and initial soil conditions, and soil chemistry effects on nutrient availability for crop uptake. Therefore, micronutrient use efficiency can be improved by adapting the rates and types of fertilizers to site-specific soil and management conditions. To make region-wide nutritional changes using agronomic biofortification, major policy interventions are needed.

In sub-Saharan Africa, there is considerable spatial and temporal variability in relations between nutrient application and crop yield, due to varying inherent soil nutrients supply, soil moisture, crop management and germplasm. This variability affects fertilizer use efficiency and crop productivity. Therefore, development of decision systems that support formulation and delivery of site-specific fertilizer recommendations is important for increased crop yield and environmental protection. Nutrient Expert (NE) is a computer-based decision support system, which enables extension advisers to generate field- or area-specific fertilizer recommendations based on yield response to fertilizer and nutrient use efficiency. We calibrated NE for major maize agroecological zones in Nigeria, Ethiopia and Tanzania, with data generated from 735 on-farm nutrient omission trials conducted between 2015 and 2017. Between 2016 and 2018, 368 NE performance trials were conducted across the three countries in which recommendations generated with NE were evaluated relative to soil-test based recommendations, the current blanket fertilizer recommendations and a control with no fertilizer applied. Although maize yield response to fertilizer differed with geographic location; on average, maize yield response to nitrogen (N), phosphorus (P) and potassium (K) were respectively 2.4, 1.6 and 0.2 t ha(-1) in Nigeria, 2.3, 0.9 and 0.2 t ha(-1) in Ethiopia, and 1.5, 0.8 and 0.2 t ha(-1) in Tanzania. Secondary and micronutrients increased maize yield only in specific areas in each country. Agronomic use efficiencies of N were 18, 22 and 13 kg grain kg(-1) N, on average, in Nigeria, Ethiopia and Tanzania, respectively. In Nigeria, NE recommended lower amounts of P by 9 and 11 kg ha(-1) and K by 24 and 38 kg ha(-1) than soil-test based and regional fertilizer recommendations, respectively. Yet maize yield (4 t ha(-1)) was similar among the three methods. Agronomic use efficiencies of P and K (300 and 250 kg kg(-1), respectively) were higher with NE than with the blanket recommendation (150 and 70 kg kg(-1)). In Ethiopia, NE and soil-test based respectively recommended lower amounts of P by 8 and 19 kg ha(-1) than the blanket recommendations, but maize yield (6 t ha(-1)) was similar among the three methods. Overall, fertilizer recommendations generated with NE maintained high maize yield, but at a lower fertilizer input cost than conventional methods. NE was effective as a simple and cost-effective decision support tool for fine-tuning fertilizer recommendations to farm-specific conditions and offers an alternative to soil testing, which is hardly available to most smallholder farmers.

Variability in crop response and nutrient use efficiencies to fertilizer application is quite common under varying soil and climatic conditions. Understanding such variability is vital to develop farm- and area- specific soil nutrient management and fertilizer recommendations. Hence the objectives of this study were to assess maize grain yield response to nutrient applications for identifying yield-limiting nutrients and to understand the magnitude of nutrient use efficiencies under varying soil and rainfall conditions. A total of 150 on-farm nutrient omission trials (NOTs) were conducted on farmers' field in high rainfall and moisture stress areas. The treatments were control, PK, NK, NP, NPK and NPK+ secondary and micronutrients. Maize grain yield, nutrient uptake, agronomic and recovery efficiencies of N and P differed between fertilizer treatments and between the contrasting agro-ecologies. The AEN ranged from 24.8 to 32.5 kg grain kg-1 N in Jimma area and from 1.0 kg grain kg-1 N (NK treatment) to 10.2 kg grain kg-1 N (NPK treatment) at Adami Tullu and from 0.1 kg grain kg-1 N (NK treatment) to 8.3 kg grain kg-1 N (NPK treatment) at Bulbula. The differing parameters between the agro-ecologies were related to difference in rainfall amount and not to soil factors. Grain yield response to N application and agronomic efficiencies of N and P were higher in the high rainfall area than in the moisture stress areas. Grain yield responded the most to nitrogen (N) application than to any other nutrients at most of the experimental sites. Owing to the magnificent yield response to N fertilizer in the current study, proper management of nitrogen is very essential for intensification of maize productivity in most maize growing areas of Ethiopia.

Nutrient limitation is a major constraint in crop production in sub-Saharan Africa (SSA). Here, we propose a generic and simple equilibrium model to estimate minimum input requirements of nitrogen, phosphorus and potassium for target yields in cereal crops under highly efficient management. The model was combined with Global Yield Gap Atlas data to explore minimum input requirements for self-sufficiency in 2050 for maize in nine countries in SSA. We estimate that yields have to increase from the current ca. 20% of water-limited yield potential to approximately 50–75% of the potential depending on the scenario investigated. Minimum nutrient input requirements must rise disproportionately more, with N input increasing 9-fold or 15-fold, because current production largely relies on soil nutrient mining, which cannot be sustained into the future.

Establishing balanced nutrient requirements for maize (Zea mays L.) in the Northern Nigerian Savanna is paramount to develop site-specific fertilizer recommendations to increase maize yield, profits of farmers and avoid negative environmental impacts of fertilizer use. The model QUEFTS (QUantitative Evaluation of Fertility of Tropical Soils) was used to estimate balanced nitrogen (N), phosphorus (P) and potassium (K) requirements for maize production in the Northern Nigerian Savanna. Data from on-farm nutrient omission trials conducted in 2015 and 2016 rainy seasons in two agro-ecological zones in the Northern Nigerian Savanna (i.e. Northern Guinea Savanna "NGS" and Sudan Savanna "SS") were used to parameterize and validate the QUEFTS model. The relations between indigenous soil N, P, and K supply and soil properties were not well described with the QUEFTS default equations and consequently new and better fitting equations were derived. The parameters of maximum accumulation (a) and dilution (d) in kg grain per kg nutrient for the QUEFTS model obtained were respectively 35 and 79 for N, 200 and 527 for P and 25 and 117 for K in the NGS zone; 32 and 79 for N, 164 and 528 for P and 24 and 136 for K in the SS zone; and 35 and 79 for N, 199 and 528 for P and 24 and 124 for K when the data of the two zones were combined. There was a close agreement between observed and parameterized QUEFTS predicted yields in each of the agro-ecological zone (R-2 = 0.69 for the NGS and 0.75 for the SS). Although with a slight reduction in the prediction power, a good fit between the observed and model predicted grain yield was also detected when the data for the two agro-ecological zones were combined (R-2 = 0.67). Therefore, across the two agro-ecological zones, the model predicted a linear relationship between grain yield and above-ground nutrient uptake until yield reached about 50 to 60% of the yield potential. When the yield target reached 60% of the potential yield (i.e. 6.0 t ha(-1)), the model showed above-ground balanced nutrient uptake of 20.7, 3.4 and 27.1 kg N, P, and K, respectively, per one tonne of maize grain. These results suggest an average NPK ratio in the plant dry matter of about 6.1:1:7.9. We concluded that the QUEFTS model can be widely used for balanced nutrient requirement estimations and development of site-specific fertilizer recommendations for maize intensification in the Northern Nigerian Savanna.

Traditional agricultural research and extension relies on replicated field experiments, on-farm trials, and demonstration plots to evaluate and adapt agronomic technologies that aim to increase productivity, reduce risk, and protect the environment for a given biophysical and socio-economic context. To date, these efforts lack a generic and robust spatial framework for ex-ante assessment that: (i) provides strategic insight to guide decisions about the number and location of testing sites, (ii) define the target domain for scaling-out a given technology or technology package, and (iii) estimate potential impact from widespread adoption of the technology(ies) being evaluated. In this study, we developed a data-rich spatial framework to guide agricultural research and development (AR&D) prioritization and to perform ex-ante impact assessment. The framework uses “technology extrapolation domains”, which delineate regions with similar climate and soil type combined with other biophysical and socio-economic factors that influence technology adoption. We provide proof of concept for the framework using a maize agronomy project in three sub-Saharan Africa countries (Ethiopia, Nigeria, and Tanzania) as a case study. We used maize area and rural population coverage as indicators to estimate potential project impact in each country. The project conducted 496 nutrient omission trials located at both on-farm and research station sites across these three countries. Reallocation of test sites towards domains with a larger proportion of national maize area could increase coverage of maize area by 79–134% and of rural population by 14–33% in Nigeria and Ethiopia. This study represents a first step in developing a generic, transparent, and scientifically robust framework to estimate ex-ante impact of AR&D programs that aim to increase food production and reduce poverty and hunger.

Diagnostic on-farm nutrient omission trials were conducted over two cropping seasons (2015 and 2016) to assess soil nutrients related constraints to maize yield in the northern Nigerian savanna agro-ecological zone and to quantify their variability. Two sets of trials were conducted side by side, one with an open pollinated maize variety (OPV) and the other one with a hybrid maize variety and each set had six equal treatments laid out in 198 farmers’ fields. The treatments comprised (i) a control, (ii) a PK (‘−N,’ without N), (iii) an NK (‘−P,’ without P), (iv) an NP (‘−K,’ without K), (v) an NPK and (vi) an NPK + S + Ca + Mg + Zn + B (‘+SMM,’ NPK plus secondary macro- and micro-nutrients). Moderate to a large variability in most soil characteristics was observed in the studied fields. Consequently, cluster analysis revealed three distinct yield-nutrient response classes common for the two types of maize varieties. These define classes were fields that have (i) no-response to any nutrient, (ii) a large response to N and P and (iii) a large response to N alone. Although overall yield performance of OPV and hybrid varieties was similar, a distinct fourth class was identified for the hybrid variety, (iv) fields with a large response to N and secondary macro- and micro-nutrients. The results indicate that the large variability in soil nutrients related constraints need to be accounted for to optimize maize yield in the northern Nigerian savanna. The development of field- and area-specific fertilizer recommendations is highly needed, using simple decision support tools that consider variable soil fertility conditions and yield responses as obtained from this study.

Climate change, increased climate variability and poor soil fertility are major bio-physical constraints to cropping on smallholder farms in southern Africa. We used the Agricultural Production Systems sIMulator (APSIM) to assess maize yield response to integrated soil fertility management (ISFM) rotational sequences of low-quality organic resources, nitrogen-fixing green manure and grain legumes, and mineral fertilizers under baseline (1960-2005) and projected (2040-2069) climates. APSIM was also employed to evaluate the response of maize yield to the ISFM sequences under a combination of a changing climate, and typical sowing dates and mineral fertilizer application rates for smallholder households of varying resource endowment. The ISFM sequences were 'Fertilizer-start' [a sunnhemp (Crotalaria juncea (L.)-based sequence], litter-start' (a woodland litter -based sequence), and 'Soya-start' and 'Manure-start' (cattle manure-based sequences). The simulated maize grain yields were used to analyze agronomic and economic risks of maize productivity. Agronomic risk was evaluated on the basis of sufficiency of the maize grain yield to meet annual household calorie (energy) requirements, while economic risk was assessed using gross margins. For model evaluation, the simulated maize yields compared well with those measured from the field experiment (RMSE = 0.11-0.55; R-2 = 0.55-0.93). Under the baseline climate, 'Soya-start' was the least risky ISFM option as only one (2.2%) of the 45 years had calories lower than the minimum acceptable limit of 4,872,750 kcal required to meet household food self-sufficiency for a family of six people. Conversely, continuous fertilized maize and 'Litter-start' were the most risky options among the fertilized treatments as three (6.7%) and four (8.9%) of the 45 years, respectively, yielded calories that were below the threshold. Across treatments, the number of years with maize grain yield exceeding 2.3 t ha(-1) was higher under baseline compared with future climate. However, 'Soya-start' and 'Manure-stare were consistently the least risky options under the future climate. The cattle manure-based sequences also had the lowest economic risk under both baseline and future climates. Over the 45-year period under baseline climate, 'Soya-start' only had two years with negative gross margins compared with six and nine for 'Litter-start' and continuous fertilized maize, respectively. A similar trend was observed under future climate. Overall, agronomic risk was lowest under sowing dates and mineral fertilizer application rates for resource-endowed (RG1) farmers compared with their resource-constrained (RG3) counterparts. Agronomic risk was higher under the representative concentration pathway (RCP) 8.5 compared with RCP4.5, with an average increase of 6, 4 and 6% for RG1, resource-intermediate (RG2) and RG3 management, respectively. Under the typical farmer management practices, the cattle manure-based sequences gave lower agronomic risk than continuous fertilized maize. Economic risk under the farmer management scenarios overly mirrored trends observed for agronomic risk. We conclude that sequenced ISFM combinations of organic resources, nitrogen-fixing green manure and grain legumes, and mineral fertilizers reduce climate risk in smallholder rainfed crop production systems in southern Africa, and similar agroecologies.