Introduction The main constraint to cowpea, Vigna unguiculata , production in West Africa is unavailability of applied phosphorus due to ligand exchange with clay minerals and precipitation reactions facilitated by low pH and low organic matter. Materials and methods To overcome this challenge, cow dung biochar (CB) and poultry litter biochar (PB) were applied as P sources for cowpea cultivation in Plinthustult and Kandiustalf soil in Ghana. The biochar types and triple super phosphate (TSP) were applied to meet the standard phosphorus requirement (SPR) and ½ SPR of the soils. Basal K from KCl was added to the TSP treatment. In addition to a non-amended soil, the treatments were triplicated and arranged in a completely randomized design in a screen house for an efficacy trial using cowpea as the test crop. Moisture content was maintained at 80% field capacity. Results and discussion Hundred cowpea seed weight was 20.3 g and 19.6 g for the TSP-amended Plinthustult at SPR and ½ SPR, respectively. This increased to 25.1 g and approximately 27 g at SPR and ½ SPR in the CB- and PB-amended Plinthustult, respectively. Hundred seed weight for TSP at both rates was similar in the two soils. The PB-amended Kandiustalf at SPR had seed with a weight of 27.02 g, 1.1 g heavier than the ½ SPR. The CB-amended Kandiustalf at both rates had 100 seeds weighing 25 g. Residual available P was 334.2 mg/kg and 213.2 mg/kg at SPR and ½ SPR, respectively, in the Plinthustult as opposed to a paltry 2.5 mg/kg at SPR in the TSP counterpart. The study recommends for the two biochar types to be applied at ½ SPR.

As an affordable method of removing phosphorus from wastewater, a vertical flow wetland was constructed in pots using a kaolinitic rich Rhodic Kandiustalf as a basal soil and rice variety, KRC Baika, as the wetland plant to remove P from a 300 mg P/L laboratory prepared wastewater. Charcoal, corncob and bagasse were added as sorbents to improve the wetland's phosphorus removal ability. The effluents were analysed weekly for phosphorus and pH. The capacity of the wetland in phosphorus removal was on the average improved by about 6%, 25% and 27%, respectively, when charcoal, bagasse and corncob were added. The P removal abilities of the components of the wetland were in the order of rice plant > substrate-sorbent > basal soil. The bagasse amended wetland is the preferred choice as in addition to significantly reducing the concentration of P in simulated wastewater, effluents pH after treatment were within acceptable standards for discharge into natural water bodies.

Purpose Market crop waste (MCW) contributes significantly to the quantity of municipal solid waste generated in sub-Saharan Africa. These wastes, however, contain high levels of plant nutrients which can be harnessed through composting to improve soil organic matter and nutrient status of impoverished tropical soils.Method In this work, annual MCWs from two urban markets in Accra, Ghana were characterized by quantifying their seasonal availabilities, primary nutrients, heavy metals concentrations and level of microbial contamination to ascertain their suitability or otherwise for composting.Results Waste generated in the rainy seasons was higher than in the dry seasons. Primary nutrients sequestered in the MCW collected were 211.1 kg N, 1.84 kg P and 89.66 kg K for both markets. Feedstock quality analysis showed heavy metal levels in the MCW were far below the contaminant levels. Moisture content of vegetable and fruit waste was 74.34 - 90.46% and far above the desired level of aerobic composting. Pathogen levels of 5.92 CFU/g E. coli and 5.41 CFU/g Salmonella in cocoyam leaves; 6.27 CFU/g total coliform and 4.74 CFU/g Enterococcus in cabbage were detected and found to be above the maximum contaminant level as per USEPA standard.Conclusion Use of cassava, plantain peduncle and corn husk as bulking agents with vegetable and fruit waste as N, P and K sources should serve as feedstock for good quality compost production.

Farmers in resource-poor areas of the Guinea Savanna zone of Ghana often face declining soil fertility due to the continuous removal of nutrient-rich harvested produce from their fields. This study focuses on the Lawra Municipality in the Guinea Savanna zone of Ghana, where low soil fertility, specifically, limits phosphorus (P) bioavailability and hinders crop production. The objective of this research is to formulate P-enhanced biochar-compost from maize stover (MS) and groundnut husk, which abound in the area, to close the nutrient loop. MS was co-composted with groundnut husk biochar at varying rates of 0, 10, 20, 30, and 40% by volume. To facilitate decomposition using the windrow system, the composting heaps were inoculated with decomposing cow dung, and the moisture content was kept at 60% throughout the monitoring period. The addition of biochar shortened the lag phase of composting. However, rates above 20% resulted in reduced degradation of MS. Biochar incorporation enriched the available phosphorus content in the final compost from 286.7 mg kg−1 in the non-biochar-compost to 320, 370, 546, and 840.0 mg kg−1 in the 10, 20, 30, and 40% biochar-compost, respectively.

Biochar is a pyrolysed biomass, incorporated into soil for improvement of soil health. Biochar added to soils holds the potential of a triple-win for livelihoods, environment and the climate. In environments where a lot of biomass is generated and poses disposable challenges, biochar remains a viable alternative for solving both agronomic and environmental problems, especially in highly degraded soils. Considerable research into biochar over the years have indicated its potential to solve many environmental problems, however there is still lack of knowledge about specific aspects of biochar production and use. Also, a number of assertions related to the positive impact of biochar in agriculture have not been well explained scientifically and verified. In Ghana, research on biochar is recent and currently uncoordinated with research outputs not clearly documented and visible. There is the urgent need to review available information on biochar research outputs in Ghana and provide expert opinion on the feasibility of embedding the technology in specific farming systems. The aim of this paper is to present an in-depth review of biochar research in Ghana, as it relates to agriculture and environmental management. Challenges to the biochar technology, formulation, feedstock availability and adoption rates are discussed. There is wide array of potential feedstocks for biochar production from agricultural residues. The -l quantity of biochar application has pronounced effect on maize grain yield where 5 t ha -l significantly yielded more maize grain than 2.5 t ha . Soils amended with cocoa pod biochar increased maize grain yield by 56 % compared to un-amended soil. Biochar can contribute to improving crop productivity on smallholdings although its supply and value chains are not formalized and the product is unfamiliar in most farming communities. Policies that integrate biochar to sustainable intensification in agriculture is recommended.

Inherent low soil fertility status limits productivity of rice in the lowland ecologies in Northern Ghana. Combining organic and inorganic nitrogen fertilizers could help to maintain the fertility of lowland soils for rice production. A screen house pot experiment was carried out to investigate the combined effect of biochar compost and inorganic nitrogen fertilizer on the nitrogen uptake and agronomic performance of rice plants grown on an eutric gleysol lowland soil. Inorganic nitrogen fertilizer alone and its combinations with different types of biochar compost (based on the proportions of biochar and compost) were used as treatment. A control (unamended soil) was also included. The incorporation of biochar compost and inorganic nitrogen fertilizer improved the growth parameters and yield components of rice plants. The combination of biochar compost and inorganic nitrogen fertilizer was also found to improve nitrogen uptake in rice plants. This practice could be the most likely viable option for alleviating lowland soil fertility issues and increasing rice productivity in Northern Ghana.

Introduction Soybean is an important legume whose nitrogen-fixing ability may be exploited to improve the fertility status of soils. In Ghana, where most of the soils are poor in fertility, cultivation of soybean presents an inexpensive way for resource-poor farmers to earn appreciable income and improve the fertility of arable land at the same time. However, the yield and N-fixing response of soybean to inoculation in most soils with poor fertility in Ghana are not well-researched. Method A screen house study on the efficacy of Histick Soy (an inoculum manufactured by a German chemical company) on improving the nodulation of soybean in P-deficient soils comprising two Plinthustalfs, Ny1 and Ny2, with a history and no history, respectively, of soybean cultivation and a Kandiustalf with no history of soybean cultivation was evaluated in Ghana. Sterile riverbed sand was included as a check. Soybean seeds were inoculated with Histick Soy at three different rates, namely, zero, half, and recommended rate, and grown in a screen house to ascertain the efficacy of the inoculant in nodulating soybean. Nitrogen was applied at 0 and 10 kg/ha, K was applied at 60 kg/ha, and P was applied at 0, 30, and 60 kg/ha. These treatments were completely randomized with four replicates at a moisture content equivalent to 80% field capacity and grown till flowering. At flowering, the number of nodules per plant was counted. A parallel experiment was carried out to physiological maturity where 100-seed weight per pot was determined. Results and discussion Results obtained revealed that plants from the uninoculated seeds in the riverbed sand and the Kandiustalf did not nodulate. In the case of Ny2, the number of nodules at harvesting was statistically similar for half and full recommended application rate of the inoculant. The uninoculated Ny2 with 4.4 average nodules per pot did not increase at half recommended application rate. At the recommended rate, nodule numbers increased 2.3-fold to 10.3. The Ny1 showed no response to inoculation. Treatments, which received the application of 60 and 30 kg P 2 O 5 /ha triggered higher responses to inoculation in low and high Bradyrhizobia populations, respectively, in the Plinthustalfs.

ABSTRACT Soil acidification in the tropics has become a more pressing issue due to its associated aluminum (Al) phytotoxicity. The chemical reactive nature of biochar can alter Al speciation in soils. The study assessed the chemical properties and Al speciation in a Ultisol and an Oxisol amended with corn cob (CC) and rice husk (RH) biochars charred at 300, 450 and 650°C in an incubation study for 120 d. pH was determined periodically while organic carbon (OC), cation exchange capacity (CEC), exchangeable base cations, exchangeable acidity, and exchangeable Al3+ were measured at the end of the incubation period. Dissolved organic carbon (DOC) and pH were also determined in soil solution from each treatment. Throughout the incubation period CC and RH biochars significantly increased soil pH, with CC biochar showing a greater effect. Similar effects were also observed for OC, CEC, and exchangeable base cations (Ca2+, Mg2+ and K+). Soil exchangeable Al3+ and exchangeable acidity, soluble Al and Al3+ activity in soil solution decreased significantly upon biochar application; it was more significant at the 650°C. Biochars at 300–450°C exhibited a more notable increase in soil DOC. At pH ≤ 5.8, Al-DOC and free Al3+ dominated in soil solution while at pH > 5.8, Al species was mainly Al-OH ions (i.e. Al(OH)2+, Al(OH)2 +, Al(OH)3, and Al(OH)4 −). Biochars at 300–450°C promoted the large formation of Al-DOC while Al-OH ions dominated in 650°C-biochar treatments. Biochar can be used to ameliorate Al phytotoxicity in tropical acid soils, particularly at 300–450°C.

The nitrates produced after mineralization from compost may be prone to leaching, especially in tropical sandy soils, because of the increased rate of nitrification and the porous nature of such soils. This may result in low nitrogen (N) use efficiency and adverse environmental effects. Inorganic nitrification inhibitors are costly and mostly unavailable in Ghana. Research on simple but effective local materials for use as nitrification inhibitors is therefore a priority. Two such materials are neem materials and biochar. Neem materials can suppress nitrifying bacteria due to their antimicrobial properties. Biochar can hold ammonium in the soil, making it temporarily unavailable to nitrifying bacteria. This study aimed to determine the efficacy of neem materials and biochar as nitrification inhibitors and their influence on nitrate leaching. In preliminary studies: 1) pot incubation was conducted for 60 days to estimate the nitrification rate with manure, compost, and NH4Cl as the N source (150 kg N/ha) in one set and neem seeds, bark, and leaves (1.25 µg azadirachtin/g) in another set, using nitrate concentrations; and 2) the ammonium sorption and desorption capacities of sawdust, rice husk, and groundnut husk biochar were determined. In the main study, pot incubation with compost as the N source but treated with milled neem seeds or bark (1.25 µg azadirachtin/g) or sawdust biochar (20 t/ha) was conducted for 60 days, in which the nitrification inhibition was determined using nitrate concentrations. A leaching experiment in columns with similar treatments and maize sown was then conducted to quantify the nitrate in leachates. A high nitrification rate was recorded in compost-amended soil, almost half that of the standard (NH4Cl). The use of sawdust biochar, which showed the highest ammonium sorption and desorption capacity, resulted in 40% nitrification inhibition that lasted the entire incubation period. The use of neem seeds with an azadirachtin concentration of 3.92 mg/g resulted in a similar nitrification inhibition, but this only lasted 40 days. Inhibition caused by both materials resulted in about a 60% reduction in nitrate leached. Thus, neem seeds (498 kg/ha) and sawdust biochar (20 mt/ha) could be used to control nitrate leaching for short-duration and long-duration crops, respectively.

Bioplant is a liquid soil conditioner that contains a consortium of beneficial fungi and bacteria manufactured by Artemis and Angel Company Limited in Bangkok. Bioplant is purported to stimulate beneficial microbial activity in soil and hence increase crop yield. However, the efficacy of Bioplant has not been evaluated on Ghanaian soils. A screen house trial was consequently conducted to evaluate the efficacy or otherwise of Bioplant on the yield of lettuce in a Rhodic Kandiustalf amended with or without compost. The soil was mixed with compost at 20 parts soil to 80 parts compost and 60 parts soil to 40 parts compost (v/v) and potted in 1.7-L pots. There was another potted soil with no compost amendment. To each of these potted soils, Bioplant was applied at four rates, viz., zero, half the manufacturer's recommended rate, the manufacturer's recommended rate, and twice the manufacturer's recommended rate, and allowed to equilibrate for 2 weeks. Seedlings of lettuce of the variety Eden were transplanted into the pots, and the treatments kept at 80% field capacity. The treatments were replicated four times in a completely randomized design. At physiological maturity, the lettuce was harvested, and fresh and dry matter yields were taken. The C and N contents and N uptake in the harvested plants were also determined. Results indicate that conditioning the soil with Bioplant at half and the manufacturer's recommended rates increased N uptake, resulting in higher carbon accumulation with concomitant increases in both fresh and dry matter yields. The results also show that amending the Rhodic Kandiustalf with Bioplant at twice the manufacturer's rate suppressed yield. Application of Bioplant at the manufacturer's recommended rate in combination with compost amended at 40 parts to 60 parts soil (v/v) saw a 47 and 90% respective significant yield increases in fresh weight and dry matter when only Bioplant was applied at the manufacturer's recommended rate. It is therefore recommended for Bioplant to be applied at the manufacturer's recommended rate of 825 mL/ha in combination with 40 parts of compost to 60 parts of soil (v/v).

A pot experiment was conducted to investigate the effect of biochar-compost on availability of P for maize cultivation in a concretionary Lixisol of northern Ghana and residual soil characteristics thereof. Sawdust biochar was co-composted with kitchen waste and cow dung in various proportions. Four biochar-composts were selected based on their superior carbon and available P content, lower pH, and electrical conductivity (EC). These were amended to attain the standard phosphorus requirement (SPR) and half the SPR of the Lixisol. Triple superphosphate and (NH4)2 SO4 were, respectively, applied as inorganic fertilizer to meet the SPR and the average total nitrogen of the selected biochar-compost treatments. A control without any soil amendment was included. Maize was grown to tasseling (eight weeks) and shoot dry matter and P uptake determined. A 2.71 to 3.71-fold increase in P uptake led to a 1.51 to 2.33-fold increase in shoot dry matter in biochar-compost-amended soils over the control. Residual soil C, pH, and total and available P in the biochar-compost-amended soils were enhanced. Biochar-composts at half the SPR level produced maize with higher shoot dry matter than the equivalent inorganic amendment at full SPR.

Rice production in Ghana has become unsustainable due to the extremely nutrient-poor soils. It is caused by inadequate soil fertility management, including the inefficient application of fertilizers. A practical solution could be the biofertilizers, Azospirillum sp. B510. We performed field trials in Ghana and Japan to compare the effects of B510 colonization on selected Ghanaian rice varieties grown. The B510 inoculation significantly enhanced the rice cultivars' growth and yield. The phenotypic characteristics observed in rice varieties Exbaika, Ex-Boako, AgraRice, and Amankwatia were mainly short length and high tillering capacity. These features are attributed to the host plant (cv. Nipponbare), from which the strain B510 was isolated. Furthermore, Azospirillum species has been identified as the dominant colonizing bacterium of rice rhizosphere across a diverse range of agroecologies in all major rice-growing regions in Ghana. Our results suggest that the utilization of B510 as a bio-fertilizer presents a promising way to improve rice growth, enhance soil fertility, and sustain rice productivity in Ghana.

Purpose Compost production technology and use are known among Ghanaians farmers. However, the long composting period averaging three months has had adverse effect on adoption. The black soldier fly (Hermetia illucens) larvae (BSFL) feed voraciously and breaks down organic wastes fast. Addition of rice husk biochar (RHB) neutralises acidity and aerates the compost. Combined application of BSFL and RHB to feedstocks could therefore reduce composting period and improve compost quality. Method Two studies were conducted with market crop waste (MCW) as feedstock. Firstly, feedstocks at two particle sizes (x < 5 mm and 5 mm < x >10 mm), with and without BSFL were evaluated to determine degradability, chemical content of the degraded residue and to select appropriate feedstock size ideal for composting. Secondly, the selected feedstocks size of between 5 mm and 10 mm were inoculated with or without BSFL and RHB of 0%. 5% 10% and 15% added. Composting trials were conducted in barrels inclined at 30 degrees to facilitate drainage. Physicochemical and biological parameters of feedstock were monitored until maturity. Results Degradability of MCW by BSFL was feedstock specific rather than feedstock size. Inoculation of BSFL and biochar addition reduced composting period from 76 to 45 days. Biochar addition at 15% increased P availability to 1882 mg kg(-1) but reduced total N to 10.5 g kg(-1) E coli levels decreased in the BSFL-biochar composts to acceptable limits. Conclusion Composting MCW with BSFL and biochar reduced composting period and improved compost quality.

The adsorption mechanisms of phosphate (PO4-P) onto cocoa pod husk (CP), corn cob (CC), rice husk (RH) and palm kernel shell (PK) biochar pyrolyzed at 300 °C and 650 °C were investigated. A series of batch experiments were undertaken to assess the effects of contact time and pH. Results show that PO4-P adsorption equilibria for the biochar types was within 6–15 h, being rapid in the 300 °C-biochar types. The equilibrium pH for maximum PO4-P adsorption varied among biochar types, ranging from of 2.6 to 4.8 and increasing with decreasing PO4-P adsorption. Pseudo-second-order and Elovich models explained the adsorption data well indicating a chemisorption process on heterogeneous biochar surface. PO4-P adsorption was controlled initially by intraparticle diffusion and subsequently by chemisorption. Per the properties of the biochars (FTIR and elemental composition) and pH (equilibrium pH and ΔpH), PO4–P was adsorbed through electrostatic attraction, surface precipitation and ligand exchange, and the relative importance of these processes differed among the biochar types. Biochar types (PK300, PK650, CP300, CP650, RH650 and CC650) that adsorbed PO4-P through surface precipitation and ligand exchange reactions can be used to remove PO4-P from wastewater since PO4-P is strongly adsorbed, controlling PO4-P enrichment of water bodies.

Adoption of rice varieties that perform well under high iron-associated (HIA) stress environments can enhance rice production in West Africa. This study reports the genetic characterization of 323 rice accessions and breeding lines cultivated in West Africa using genotyping-by-sequencing and their phenotypic response to HIA treatments in hydroponic solution (1500 mg l-1 FeSO4·7H2O) and hot-spot fields. The germplasm consisted of four genetic subpopulations: Oryza glaberrima (14%), O. sativa-japonica (7%), O. sativa-indica Group 1 (45%), and O. sativa-indica Group 2 (25%). Severe versus mild stress in the field was associated with a reduced SPAD value (12%), biomass (56%), and grain yield (57%), with leaf bronzing explaining 30% and 21% of the variation for biomass and grain yield, respectively. Association mapping using 175 indica genotypes identified 23 significant single nucleotide polymorphism (SNP) markers that mapped to 14 genomic regions. Genome-wide association study (GWAS) signals associated with leaf bronzing, a routinely used indicator of HIA stress, differed in hydroponic compared with field conditions. Contrastingly, six significant SNPs on chromosomes 8 and 9 were associated with the SPAD value under HIA stress in both field and hydroponic experiments, and a candidate potassium transporter gene mapped under the peak on chromosome 8. This study helps define criteria for assessing rice performance under HIA environments.

The adsorption mechanisms of phosphate (PO4-P) onto cocoa pod husk (CP), corn cob (CC), rice husk (RH) and palm kernel shell (PK) biochar pyrolyzed at 300 degrees C and 650 degrees C were investigated. A series of batch experiments were undertaken to assess the effects of contact time and pH. Results show that PO4-P adsorption equilibria for the biochar types was within 6-15 h, being rapid in the 300 degrees C-biochar types. The equilibrium pH for maximum PO4-P adsorption varied among biochar types, ranging from of 2.6 to 4.8 and increasing with decreasing PO4-P adsorption. Pseudo-second-order and Elovich models explained the adsorption data well indicating a chemisorption process on heterogeneous biochar surface. PO4-P adsorption was controlled initially by intraparticle diffusion and subsequently by chemisorption. Per the properties of the biochars (FTIR and elemental composition) and pH (equilibrium pH and Delta pH), PO4-P was adsorbed through electrostatic attraction, surface precipitation and ligand exchange, and the relative importance of these processes differed among the biochar types. Biochar types (PK300, PK650, CP300, CP650, RH650 and CC650) that adsorbed PO4-P through surface precipitation and ligand exchange reactions can be used to remove PO4-P from wastewater since PO4-P is strongly adsorbed, controlling PO4-P enrichment of water bodies. (C) 2019 Elsevier B.V. All rights reserved.

The formation of phosphorus (P) compounds including iron-P, aluminum-P and calcium-P in highly weathered tropical soils can be altered upon biochar addition. We investigated the effect of corn cob biochar (CC) and rice husk biochar (RH) pyrolyzed at three temperatures (300 degrees C, 450 degrees C and 650 degrees C) on phosphorus (P) fractions of three contrasting soils. A 90d incubation study was conducted by mixing biochar with soil at a rate of 1% w/w and at 70% field capacity. Sequential P fraction was performed on biochar, soil and soil-biochar mixtures. Increase in most labile P (resin-P-i, NaHCO3-P-i) and organic P fraction (NaHCO3-P-o+ NaOH-P-o) in CC and RH biochars were inversely related to increasing temperature. HCl-P(i)and residual P increased with increasing temperature. Interaction of CC and RH with soils resulted in an increase in most labile P as well as moderately labile P (NaOH-P-i) fractions in the soils. CC increased most labile P in the soils more than RH. The increase in most labile P fraction in soils was more significant at relatively lower temperatures (300 degrees C and 450 degrees C) than 650 degrees C. However, the increase in HCl-P(i)and residual P of the soils was more predominant at high temperature (650 degrees C). The study suggested that biochar pyrolyzed at 300-450 degrees C could be used to increase P bioavailability in tropical soils.

Aside the characterization of feedstocks and biochars (BCs), the nonlinear sorption of phosphorus (P) onto corn cob (CC), rice husk (RH), cocoa pod husk (CP) and palm kernel shell (PK) BCs charred at 300, 450 and 650 degrees C were investigated using series of batch experiments. Conversion of feedstock to BC resulted in a higher pH, C content, ash, fixed C, surface area (SA) and lower volatile matter, moisture, H, N, O and S contents. Increasing pyrolysis temperature proportionally decreased the polarity (O/C, O+N/C, and O+ N+ S/C), volatile matter, moisture content, readily labile organic C and potentially unstable C vis-a-vis an increased in C content, fixed C, stable C and aromaticity (H/C). The nonlinearity index (n) as well as P sorption capacity (K-F) increased with temperature and were highly dependent on BC properties. Significant linear relationships were observed between P sorption parameters (n and K-F) and O content, polarity, aromaticity, fixed C, stable C, readily labile organic C and SA. The low polarity and high aromaticity and SA resulted in the high nonlinear sorption of P at 650 degrees C. Findings of this study provides insight into P sorption behaviour, thereby serving as a theoretical basis for biochar application either agronomically or environmentally. (c) 2020 Elsevier B.V. All rights reserved.

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.

The study investigated the changes in properties of rice husk and corn cob biochars applied in urban agricultural field soils in Tamale (northern Ghana) and Ouagadougou (Burkina Faso), respectively. The biochars were both pyrolyzed at 500 °C with a batch reactor. Fine polyethylene mesh (litter bags) filled with 10 g of each type of biochar were buried at 20 cm depth in urban fields trials with a 3 x 2 factorial layout replicated 4 times. Factor 1 involved soil management practices at 3 levels: (1) farmers’ practice (FP), (2) 20 t biochar ha-1 and (3) control (no biochar). The second factor was time (duration) at two levels (6 and 12 months). Aged and fresh biochars were analyzed for volatile matter (VM), ash and fixed carbon (FC) contents, pH, effective cation exchange capacity (ECEC), and total surface acidity (Sa) and basicity (Sb). Dissolved organic carbon contents were determined sequentially by cold (cDOC) and hot water extractions (hDOC), respectively and aromaticities of cold water DOC (cSUVA) and hot water DOC (hSUVA) were determined. There was no significant interaction effect of soil management practices and time on measured ageing biochar properties. Time significantly affected most biochar ageing properties except Sa and Sb in rice husk biochar and ECEC in corn cob biochars at 6 months of exposure. In both biochars, Ash content, Fixed carbon (FC), cDOC, hDOC, cSUVA and hSUVA increased whilst pH and volatile matter contents decreased significantly. The hDOC was 2-3 times higher than cDOC contents for both biochars. Aromaticity of DOC contents of aged rice husk biochar exposed to soil management practices and time in the experimental site in Tamale showed persistence with time compared to corn cob biochar exposed in Ouagadougou experimental site. The results imply that rainfall, soil organic matter contents with interplay of soil minerals are key drivers to ageing and sequestration of these biochars and that these forces act at different scales but driven by time.