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The adverse effects of long-term usage of synthetic fertilizers such as eutrophication, weed infestation, opportunistic diseases, and declining yields have been established. However, the fact that soil fertility declines because of continuous cropping to meet the demand for feeding the ever-growing population, coupled with the high cost of chemical fertilizers, has left little option. This mainly affects resource-poor smallholder farmers, who heavily depend on their production for sustenance and economic well-being. Current research efforts have underscored the urgency of mitigating this trend by seeking a cost-effective and eco-friendly alternative to avert impending global food crises. Biochar has gained attention as a possible alternative to meet the soil requirements on many fronts, such as improving soil functioning and restoring degraded lands. Biochar is also known to reduce heavy metal mobility and inorganic contaminants, mitigating salinity and drought stress as well as greenhouse gas emissions associated with agriculture. However, these studies need to be harmonized to draft a more pragmatic approach to policy formulation and establish an enhanced paradigm. In this paper, we review several studies on biochar and synthesize its possible use as an alternative or supplement to synthetic fertilizers to enhance crop productivity under standard and stressful growing conditions. The ability of biochar to sequester carbon and its impact on soil properties are highlighted. We emphasize its potential for soil nutrient management and the possibility of adopting it as an alternative to synthetic fertilizer in smallholder farming. We also point out several critical research gaps that call for attention and serve as pointers for future research. [ABSTRACT FROM AUTHOR]

Background: Soil fertility decline due to nutrient mining coupled with low inorganic fertilizer usage is a major cause of low crop yields across sub-Saharan Africa. Recently, biochar potential to improve soil fertility has gained significant attention but there are limited studies on the use of biochar as an alternative to inorganic fertilizers. In this study, we determined the effect of maize stover biochar without inorganic fertilizers on soil chemical properties, growth and yield of tomatoes (Solanum lycopersicum L.). A field experiment was conducted in 2022 for two consecutive seasons in Northern Uganda. The experiment included five treatments; inorganic fertilizer (control), biochar applied at rates of 3.5, 6.9, 13.8 and 27.6 t ha−1. Results: In this study, maize stover biochar improved all the soil chemical properties. Compared to the control, pH significantly increased by 27% in the 27.6 t ha−1 while total N increased by 35.6% in the 13.8 t ha−1. Although P was significantly low in the 3.5 t ha−1, 6.9 t ha−1 and 13.8 t ha−1, it increased by 3.9% in the 27.6 t ha−1. Exchangeable K was significantly increased by 42.7% and 56.7% in the 13.8 t ha−1 and 27.6 t ha−1 respectively. Exchangeable Ca and Mg were also higher in the biochar treatment than the control. Results also showed that plant height, shoot weight, and all yield parameters were significantly higher in the inorganic fertilizer treatment than in the 3.5, 6.9, and 13.8 t ha−1 treatments. Interestingly, maize stover biochar at 27. 6 t ha−1 increased fruit yield by 16.1% compared to the control suggesting it could be used as an alternative to inorganic fertilizer. Conclusions: Maize stover biochar applied at 27.6 t ha−1 improved soil chemical properties especially pH, N, P and K promoting growth and yield of tomatoes. Therefore, maize stover biochar could be recommended as an alternative to expensive inorganic fertilizers for tomato production in Northern Uganda. [ABSTRACT FROM AUTHOR]

Biochar is an effective soil amendment with capabilities of boosting carbon sequestration and enhancing soil fertility, thus enhancing plant growth and productivity. While numerous studies have documented the positive effects of biochar on improving soil properties, a number of studies have reported conflicting results. Therefore, the current study was conducted to evaluate the impact of Prosopis juliflora biochar (0, 2.5, 5.0, and 7.5 t ha−1) on soil biochemical properties in Coastal Kenya to ascertain biochar's potential for soil fertility improvement. A randomized complete block design was used for setting up the experiment with three replicates, while Casuarina equisetifolia L. was planted as the test crop. Soil sampling for nutrient analysis was conducted quarterly for 12 months to assess nutrient dynamics under different biochar rates in the current study. Compared to soil untreated with Prosopis juliflora biochar, the results showed that there was a significant increase in soil pH by 21% following biochar utilization at the rate of 7.5 t ha−1. Total nitrogen was increased by 32% after the biochar application, whereas the total organic carbon was increased by four folds in comparison to biochar-untreated soil. Available phosphorus was increased by 264% following biochar application in comparison to the control treatment. In addition, the application of biochar resulted in an increment in the soil exchangeable cations (Ca2+, K+, Mg2+) across the assessment periods. Soil cation exchange capacity (CEC), bacteria and fungi were enhanced by 95, 33 and 48%, respectively, following biochar application at 7.5 t ha−1 in comparison to untreated soil. In conclusion, these results strongly suggest improvement of soil biochemical properties following Prosopis juliflora biochar application, thus providing potential for soil fertility improvement in regions such as the one in the study. [ABSTRACT FROM AUTHOR]

The difficulty in obtaining commercial fertilizers by smallholder farmers in sub-Saharan Africa makes it very important to optimize the use of local organic resources. In VilanKulo, Mozambique, a study was carried out on okra (Abelmoschus esculentus) over two growing seasons. The soil was a haplic, loamy-sand textured Lixisol. As organic amendments, bat guano and biochar were used. Bat guano is a phosphorus (P)-rich and low-carbon (C)/nitrogen (N)-ratio material from natural deposits on a cave floor. Biochar is a C-rich material prepared via an artisanal process using forest residues as a feedstock. Bat guano was applied at two rates (5 and 10 t ha−1) just before sowing. It was also applied at the same rates one month before sowing. Biochar was used at two rates (5 and 10 t ha−1) applied at sowing. Biochar and guano were mixed at the rates of 1 and 4 t ha−1 and 2 and 8 t ha−1, respectively, and applied at sowing. The experiment also used a non-fertilized control. Field trials were arranged in a completely randomized design with three replicates. The treatments that received high rates of guano tended to show significantly higher fruit yields (>10 t ha−1 as the two-year average) in comparison with the control, which showed the lowest average okra fruit yield (6.21 t ha−1). In the guano treatments, the apparent recovery by okra of some important nutrients, such as N, was greater than the amount of the nutrient contained in the guano itself. This result, together with many others related to the tissue nutrient concentration, soil properties and residual fertilizing value in guano plots, indicated a strong mineralization of guano during the growing season. This was probably due to its low C/N ratio and favourable environmental conditions for the mineralization process. The result also suggests some kind of manuring effect, i.e., a fertilizing effect of guano beyond what can be explained by the nutrient supply. The use of biochar increased the total organic C in the soil and cation exchange capacity (CEC) compared with the control but did not affect the variables related to plant performance. Overall, the results showed that farmers can benefit from the use of guano in the short term because it releases nutrients, while with the use of biochar, the benefits can arise in the long term by improving the soil properties. [ABSTRACT FROM AUTHOR]

In sub-Saharan Africa, soil fertility management must rely on local fertiliser resources since most smallholder farmers do not have access to industrial fertilisers. In Vilankulo, Mozambique, farmers have access to bat guano and biochar, albeit in small amounts, which makes it even more necessary to manage them correctly to maximise crop productivity. This study was carried out with irrigated maize (Zea mays L.) in a haplic Lixisol during the 2017/2018 and 2019 growing seasons. Nine treatments were established consisting of the application of 5 (G5) and 10 (G10) t ha−1 of guano at sowing, 5 (B5) and 10 (B10) t ha−1 of biochar at sowing, 5 [G5(-1)] and 10 [G10(-1)] t ha−1 of guano one month before sowing, 1 and 4 (B1G4) and 2 and 8 (B2G8) t ha−1 of biochar and guano, respectively, at sowing and an unfertilised control (C). Treatments G10 and B2G8 led to the highest maize yields (3.77 and 2.68 t ha−1 in 2018 and 5.05 and 5.17 t ha−1 in 2019, respectively), and were statistically higher than those of the control (1.35 and 1.63 kg ha−1, respectively). Apparent nitrogen recovery from bat guano was close to 100%, showing almost complete mineralisation during the maize growing season, due to its low carbon/nitrogen ratio and very favourable environmental conditions for mineralisation. Due to the fast release of nutrients, bringing forward the application of the organic amendment before sowing is not recommended, since it reduces nutrient use efficiency. Biochar did not significantly influence maize grain yield or contribute significantly to plant nutrition. To take advantage of its potential effect on some soil properties, its use in combination with other materials of greater fertilising value is recommended. [ABSTRACT FROM AUTHOR]

Cacao pod husk biochar was used as an adsorbent for the adsorption of toxic metals from aqueous phase. Cacao pod husk signifies a readily available source of eco-friendly and low-cost adsorbent in Sub-Saharan Africa that has scarcely been paid attention to. The experiment was conducted in a monosystem to determine how cacao pod husk biochar can efficiently adsorb lead (Pb2+), mercury (Hg2+) and cadmium (Cd2+) from aqueous phase. The experiment was conducted with 100 mL of varied toxic metal concentrations of the aqueous phase with a contact time of 60 min and a constant rotary speed of 14.8 U/min. The removal efficiency of cacao pod husk biochar for Pb2+, Hg2+ and Cd2+ ranged from 99.20 to 99.94%, 99.97 to 99.99%, and 99.85 to 99.99%, respectively. Freundlich adsorption isotherm was favourable for the adsorption of toxic metals onto the cacao pod husk biochar. The toxic metals had a stronger binding affinity to the cacao pod husk biochar. Hence, cacao pod husk was efficient for toxic metals elimination. [ABSTRACT FROM AUTHOR]

Background: The residual effects of biochar are yet to receive adequate research attention in Sub-Saharan Africa despite the assumption that the positive effect of biochar may last longer on degraded tropical soil. Hence a field experiment was conducted to assess the residual effects of biochar, farmyard compost and NPK fertilizer applications on a Ferralsol in central Uganda. The field used for the study was previously used to conduct experiments for two seasons to assess the contribution of corncob biochar to the chemical properties of this highly degraded tropical soil. Result: The co-applied biochar with compost and NPK fertilizer significantly (p < 0.05) increased some soil chemical properties such as soil pH, available phosphorus, soil organic carbon, and potassium than the control. The co-applied biochar with compost also significantly (p < 0.05) increased the soil pH and effective cation exchange capacity compared to the solely applied compost and NPK fertilizer. Collard plant height, canopy, stem girth, number of leaves, leaf length, and total biomass were significantly (p < 0.05) higher in the biochar amended soil than the unamended soil. Conclusion: It was concluded that the addition of biochar with compost and NPK fertilizer had a significant residual effect on degraded tropical soils than solely applied NPK and compost. [ABSTRACT FROM AUTHOR]

Soil erosion, starvation, livelihood protection, energy shortages, and environmental pollution are major concerns in Sub-Saharan Africa (SSA). Biochar has become an issue of international concern, but little research has investigated biochar's capacity to alleviate SSA challenges. This review defines and evaluates biochar's ability and constraints in SSA by undertaking a case study in Cote d'Ivoire. The specific goals were to (1) describe and assess biochar feedstocks; (2) conduct an overview of the literature on biochar production technology; (3) explore its potential uses in agriculture, energy, and environmental remediation; and (4) identify barriers to research implementation and future biochar research. Furthermore, the potential agricultural and environmental benefits of biochar are addressed. According to these results, Cote d'Ivoire's plentiful crop supplies represent a major opportunity for biochar production. Biochar has promising application in agriculture and the environment by improving soil fertility and crop productivity, sequestering CO 2 and reducing greenhouse gas emissions, and remediating polluted water and soils. Biochar is an excellent alternative to traditional coal for producing clean energy, especially for low-income households without access to reliable electricity. To reap biochar's benefit within SSA, researchers, customers, and the general public need to overcome various challenges, including environmental, socioeconomic, and logistical constraints. Therefore, many research projects would be expected to show the value of biochar applications, set guidelines for their use, and ultimately, develop a policy and standards for their eventual implementation. [Display omitted] • Biochar research is lacking in Sub-Saharan Africa, including Cote d'Ivoire. • In Cote d'Ivoire, biomass feedstocks are broadly available for biochar production. • Low-cost and reliable pyrolyzers are required for effective biochar production. • Biochar is applied in agriculture, energy, and environmental remediation. • Biochar is restricted by socio-economic obstacles and empirical data in SSA. [ABSTRACT FROM AUTHOR]

Biochar has received considerable scientific attention in the past decade as a possible method for carbon storage and increasing agricultural yields. Despite this promise, however, economic assessments of biochar are yet to definitively establish the value of the technology, primarily due to discrepancy between observed short-term agronomic benefits and expectations of biochar as a lasting soil improver. This study investigated the economic value of biochar as an agricultural technology for long-term improvement of arable farming. From presently available field trial data, the costs and benefits of using biochar technology to enhance cereals agriculture were evaluated in two generalized geo-economic agricultural scenarios: North-Western Europe ( NWE) and Sub-Saharan Africa ( SSA). Cost models were developed to estimate the total cost of biochar from initial biomass feedstock acquisition to final soil application for each agricultural setting. Benefits of biochar application were estimated by statistical meta-analysis of crop yield data from published biochar field trials to find the increase in cereal grain yield attributable to biochar application for both NWE (+0.07 to +0.28 t ha−1 yr−1) and SSA (+0.18 to +1.00 t ha−1 yr−1). The grain yield improvement from a one-time biochar application was assumed to persist without decay for an independently varying time period, and the increase in grain production then monetised using projected future commodity prices. The Net Present Value ( NPV) of applying biochar was then calculated by setting present total costs against present total benefits as a function of biochar performance longevity. Biochar application was found to carry a positive NPV for cereal cropping in SSA in several scenarios where the duration of the biochar yield effect was assumed to extend 30 years into the future. Conversely, NWE biochar scenarios were all found to have negative NPVs even when the benefits time span was indefinitely stretched. [ABSTRACT FROM AUTHOR]

Sub-Saharan Africa (SSA) experiences soil degradation, food and livelihood insecurity, environmental pollution and lack of access to energy. Biochar has gained international research attention, but few studies have investigated the potential of biochar to address the challenges in SSA. This paper seeks to identify and evaluate generic potential opportunities and constraints associated with biochar application in sub-Saharan Africa using Zimbabwe as case study. Specific objectives were to; (1) identify and quantify feedstocks for biochar production; (2) review literature on the biochar properties, and evaluate its potential applications in agriculture, environmental remediation and energy provision, and (3) identify research gaps, risks and constraints associated with biochar technology. Biochar feedstocks in Zimbabwe were estimated to be 9.9 Mton yr −1 , predominantly derived from manure (88%) and firewood (10%). This will yield 3.5, 1.7 and 3.1 Mton yr −1 of biochar, bio-oil and synthetic gas, respectively. Land application of the 3.5 Mton yr −1 of biochar (≈63% C) would sequester approximately 2.2 Mton yr −1 of soil carbon in Zimbabwe alone, while simultaneously minimizing the environmental and public health risks, and greenhouse gas emissions associated with solid organic wastes. Biochar potentially enhances soil and crop productivity through enhanced nutrient and soil moisture availability, amelioration of acidic soils and stimulation of microbial diversity and activity. Due to its excellent adsorption properties, biochar has potential applications in industrial and environmental applications including water and wastewater treatment, remediation and revegetation of contaminated soils and water. Biochar products have energy values comparable or higher than those of traditional biomass fuels; thereby making them ideal alternative sources of energy especially for poor households without access to electricity. Before the benefits of biochar can be realized in SSA, there is need to overcome multiple risks and constraints such as lack of finance, socio-economic constraints including negative perceptions and attitudes among both researchers and consumers, and environmental and public health risks. Therefore, there is need to conduct fundamental research to demonstrate the benefits of biochar applications, and develop policy framework and criteria for its production and subsequent adoption. [ABSTRACT FROM AUTHOR]

Rice husk biochar (RHB) and phosphate rock (PR) are locally accessible resources that poor farmers in Sub-Saharan Africa (SSA) can utilize to increase rice productivity. However, biochars are variable depending on feedstock, pyrolysis temperature, and duration. Phosphate rocks from SSA are of low solubility. The goal of this study was to determine whether pyrolysis of rice husk (RH), calcination of PR, and the calcination/pyrolysis of a RHB-PR mixture at 300 °C, 500 °C, and 700 °C can increase formic acid (FA)- extractable phosphorous (P). The properties of these RHBs were compared to the properties of RHB produced through a simple farmer-friendly pyrolysis technique termed "Kun-tan". Properties of calcinated PR were also compared to the raw PR. Quartz formed from amorphous SiO2 during RH pyrolysis and was the dominant mineral phase in the biochars, irrespective of the pyrolysis temperature. Formic acid-extractable P content, pH, and ash content of the biochars increased with increasing pyrolysis temperature. At 700 °C, FA-extractable P content of the RHB was 219% more than the feedstock. Hydroxyapatite and quartz were the dominant minerals in the PR irrespective of calcination temperature, indicating that hydroxyapatite and quartz were stable to at least 700 °C. Rather, calcination decreased the FA-extractable P content of the PR. [ABSTRACT FROM AUTHOR]

Energy access and waste management are two of the most pressing developmental and environmental issues on a global level to help mitigate the accelerating impacts of climate change. They are particularly relevant in Sub–Saharan Africa where electrification rates are significantly below global averages and rural areas are lacking a formal waste management sector. This paper explores the potential of integrating solar energy into a biomass pyrolysis unit as a potentially synergetic solution to both issues. The full design of a slow pyrolysis batch reactor targeted at biochar production, following a strict cost minimization approach, is presented in light of the relevant considerations. SPEAR is powered using a Cassegrain optics parabolic dish system, integrated into the reactor via a manual tracking system and optically optimized with a Monte-Carlo ray tracing methodology. The design approach employed has led to the development an overall cost efficient system, with the potential to achieve optical efficiencies up 72% under a 1.5° tracking error. The outputs of the system are biochar and electricity, to be used for soil amendment and energy access purposes, respectively. There is potential to pyrolyze a number of agricultural waste streams for the region, producing at least 5 kg of biochar per unit per day depending on the feedstock employed. Financial assessment of SPEAR yields a positive Net Present Value (NPV) in nearly all scenarios evaluated and a reasonable competitiveness with small scale solar for electrification objectives. Finally, SPEAR presents important positive social and environmental externalities and should be feasibly implementable in the region in the near term. [ABSTRACT FROM AUTHOR]

The efficiency of mineral fertilizer use in most soils in Sub-saharan Africa is low. Prominent among the reasons for this is low soil carbon stock. In this study, we hypothesized that in the short term, combined use of biochar and inorganic fertilizer in irrigated rice (Oryza sativa var KRC Baika) cropping systems will increase soil organic carbon storage, N recovery and agronomic efficiency of N use (above world average of 55% and 20 kg grain·kg−1·N respectively) and improved economic returns compared to the sole use of inorganic fertilizer. A two-year (4‒cropping cycles) field trial was, thus, conducted on a Vertisol. The experiments were designed as split–plot with two (0 and 10 t·ha−1) biochar and four (0, 45, 90, 120 kg·ha−1·N) nitrogen application rates. Additionally, the effect of biochar on the chemical properties of the soil was investigated using standard protocols. Biochar application improved the soil organic carbon storage in the topsoil. There were significant interactions between the application of biochar and nitrogen fertilizer on yield parameters. Introducing biochar significantly increased root volume and nutrient (N, P and K) uptake, resulting in increased grain and straw yield. Grain yields under biochar amended plots were higher than sole fertilizer amended plots in 14 out of 16 instances (cropping cycles × N rates). The increase in grain yield was between 12 to 29% across N rates. Biochar amendment also enhanced agronomic N use and apparent N recovery efficiencies in 3 out of the 4 cropping cycles. Gross margin indicated that biochar application under irrigated rice cropping systems is economically feasible in all cropping cycles and N rates. However, the value cost ratio of biochar application was higher than for sole inorganic fertilizer in three out of the four cropping cycles (each cropping cycle has three N rates). The soil organic carbon storage of biochar amended soil increased by 17% under unfertilized condition and by 32% under fertilized condition. To enable the promotion and efficient use of the biochar technology in enhancing productivity and profitability in irrigated rice, extension officers and farmers will need to be trained on how to char the rice husk to reduce emissions prior to upscaling the technology to farmers. [ABSTRACT FROM AUTHOR]

Conservation agriculture (CA) as a system is still evolving on many of the smallholder farms in sub-Saharan Africa (SSA) and questions on the impact of individual components and pathways toward adoption still require answers. A short-term study was conducted to investigate the effect of tillage, crop rotation, and crop residue management, including maize residue biochar on above ground biomass, cumulative carbon (C) input, soil organic carbon (SOC), and maize grain yield. A split–split plot design was used to evaluate two tillage operations (conventional tillage (CT) and no-till (NT)), three crop rotations (maize–fallow–maize (MFM), maize–oat–maize (MOM), and maize–vetch–maize (MVM)), and three-crop residue management (retention (R+), removal (R−), and biochar (B)). The cumulative above ground biomass produced in the MOM rotation was significantly higher by 78.9% and 88.7% relative to MVM and MFM rotations, respectively. The cumulative C input under residue management treatments ranged from 10.65 to 12.16 Mg ha−1. The highest SOC was observed under R+ (1.10%) followed by B (1.0%) and the lowest was in R− (0.96%). Crop residue management significantly affected grain yields in 2015/2016 (p < 0.05) and 2016/2017 (p < 0.01) summer seasons. Biochar did not result in an obvious improvement in both C input and crop yield. Smallholder farmers can potentially switch from CT to NT without any significant yield penalty, as well as adopt MOM and R+ practices for increased biomass and C input. [ABSTRACT FROM AUTHOR]

The dependency on rainfed agriculture and weak adaptability of the agricultural sector to climate change threaten food security in Sub-Saharan Africa (SSA). Biochar has widely been touted as a relatively easy means of increasing the soil water storage capacity of soils and thereby improving or maintaining crop yields. In this study we simulated the effect of biochar amendment on sorghum aboveground biomass and grain yield at a site in South Sudan. We used the model AquaCrop parameterized using site, soil, and cropping management data from a field experiment carried out at the site in 2011 and 2012, which were both wet years. Changes in soil hydraulic properties due to biochar were based on a published meta-analysis study. In order to investigate whether the response to biochar differed in dry years, simulations were also carried out for 1990, which was the driest year during the period 1979–2014. Measured and modelled biomass and yields with and without biochar for 2011 and 2012 were compared. Simulated and measured yields depended on growing season rainfall and distribution. The simulations showed that biochar amendment had an effect on rooting zone soil water content and sorghum biomass and grain yield in 1990, but not in 2011 and 2012. In view of expected climate change, the results have important implications for sorghum production and the potential use of biochar in SSA. Given the limited response of grain yield to biochar shown in our simulations, careful selection of sorghum variety and cultivar and consideration of planting date may be a more effective means of improving yields than applying biochar. [ABSTRACT FROM AUTHOR]

Biomass fuels dominate the household energy mix in sub-Saharan Africa. Much of it is used inefficiently in poorly ventilated kitchens resulting in indoor air pollution and consumption of large amounts of wood fuel. Micro-gasification cookstoves can improve fuel use efficiency and reduce indoor air pollution while producing char as a by-product. This study monitored real-time concentrations of carbon monoxide (CO), carbon dioxide (CO2) and fine particulate matter (PM2.5), and amount of firewood used when households were cooking dinner. Twenty-five households used the gasifier cookstove to cook and five repeated the same test with three-stone open fire on a different date. With the gasifier, the average corresponding dinner time CO, CO2, and PM2.5 concentrations were reduced by 57%, 41%, and 79% respectively compared to three-stone open fire. The gasifier had average biomass-to-char conversion efficiency of 16.6%. If the produced char is used as fuel, households could save 32% of fuel compared to use of three-stone open fire and 18% when char is used as biochar, for instance. Adoption of the gasifier can help to reduce the need for firewood collection, hence reducing impacts on the environment while saving on the amount of time and money spent on cooking fuel. [ABSTRACT FROM AUTHOR]