ABSTRACT Background Carbonized organic matter (biochar) and compost are both beneficial soil amendments and particularly meaningful for the restoration of degraded soils. Application of biochar adds stable carbon (C) but only little nitrogen (N) to the soil. Compost is rich in C and N, but losses of these elements during composting are large, and C stability is relatively low. The addition of biochar during composting has been reported to decrease N losses, accelerate the composting process, increase cation exchange capacity (CEC), and increase water‐holding capacity compared to composting without biochar. However, C and N dynamics during biochar co‐composting vary enormously depending on feedstock quality. Aims Therefore, the aims of this study were to find out if biochar addition will reduce C and N losses during composting of organic materials in a field trial in Sub‐Saharan Africa or not. Methods Six compost treatments, among them three compost mixtures with biochars made from rice husks (cRH), corn cobs (cCC) and wood (cWO) or their un‐carbonized feedstocks (RH, CC, and WO), were co‐composted with poultry manure (15 vol‐%) and rice straw (60 vol‐%) in randomly allocated 1 m 3 compost bins. Results After composting, biochar treatments had lower or similar C losses, lower contents of dissolved organic carbon (DOC), higher C decomposition rates, and higher or similar pH‐values compared with their non‐biochar treatments. Biochars that were stored in mesh bags during composting increased in DOC and effective CEC and decreased in surface area. Biochar retained N through accumulation and sorption of ammonium nitrogen (NH 4 ‐N). Microbial biomass and nitrate nitrogen (NO 3 ‐N) were similar among all treatments. Conclusions Overall, biochar positively affected C and N retention and compost quality.

Biochar application can improve soil quality and plant growth, particularly in combination with organic and mineral fertilization. However, data on its effectiveness in intensively managed (fertilized) gardens within the urban and peri-urban (UPA) agriculture of West Africa is sketchy. We, therefore, studied the medium-term effects of repeated biochar produced from agricultural residues, composted faecal amendments (ECOSAN), and inorganic fertilization on small-scale, intensive urban vegetable production in multiple crop rotations over four years. The experiment used a randomized factorial design comprising different soil management and irrigation practices on a Haplic Lixisol in Ouagadougou, Burkina Faso during eight cropping cycles. Biochar amendment resulted in increased soil organic carbon (SOC) on plots under farmers' practice (cattle manure + urea). Repeated biochar application at 20 t ha(-1) increased SOC by 51 %. Mineral fertilization alone decreased SOC by 32 % (from 12.7 to 8.6 g C kg(-1) soil) after 6 months with a progressive decline and soil acidification over time. During this period fertilization with ECOSAN at 16-23 t ha(-1) per cropping cycle increased yields and soil pH from 6.5 to 7.4. Four years after its application biochar still increased total fresh matter yield of cabbage by 32 % but showed no effect on amaranth while repeated biochar application only increased total fresh matter yields of the first crop after reapplication. Nitrogen use efficiency (NUE) was higher with mineral fertilizer (NPK) and mineral fertilizer in combination with organic fertilizer (FP) than with ECOSAN alone. The study demonstrates effect of biochar on SOC with less pronounced, crop-specific agronomic benefits.

BackgroundLittle is known about the effects of gypsum application to remediate saline-sodic soils in the tropics and the role of microbial indicators in soil reclamation. AimsOur study aimed at (1) remediating a highly weathered, irrigated sodic Lixisol under prolonged urban crop production by clean water and gypsum application and (2) to determine the remediation effects on soil microbial indices. MethodsA three-factorial on-farm experiment with maize (Zea mays L.) was used to study effects on soil microbial biomass of (1) soil degradation at two levels of salinity, (2) irrigation with clean water and wastewater, and (3) the impact of added gypsum during a typical growing season. ResultsAt the high-degradation site, the 0.5 M K2SO4 extractable carbon (C) content was 40% higher than at the low-degradation site. In addition, microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) were 20% lower than at the low-degradation site, while fungal ergosterol was even 40% lower, leading to a 33% lower ergosterol/MBC ratio. Wastewater irrigation increased MBN but decreased ergosterol content at the low-degradation site while having no effect at the high-degradation site. Gypsum amendment led to higher MBN at the low-degradation site but to lower MBN at the high-degradation site. Gypsum amendment always increased the ergosterol content whereby this increase was stronger at the low-degradation site, especially in combination with wastewater irrigation. ConclusionsFrom a microbial perspective, high soil degradation levels should be avoided by treatment of a saline-sodic wastewater prior to its use for irrigation rather than relying on future remediation strategies of affected field sites.

Background Intensive wastewater irrigated urban horticulture in sub-Saharan West Africa receives high nutrient inputs, which lead to large gaseous and leaching losses. The addition of biochar to the usually sandy soils may reduce these losses and improve the habitat conditions for soil microorganisms. Two similar experiments focused on crop yields and nutrient balances have been carried out over a 2-year period in semi-arid Ouagadougou, Burkina Faso, and in sub-humid Tamale, Ghana, representing to some extent different but typical locations in West Africa. Methods Biochar and N fertilization effects were measured on soil microbial biomass carbon (MBC), fungal ergosterol, and functional diversity, estimated by multi-substrate-induced respiration. It was additionally possible to study the effects of clean water irrigation on the respective microbial properties in Tamale soil. Results Sole biochar addition did not affect any soil chemical or soil biological properties analyzed. In contrast, biochar application with N fertilization increased the mean respiratory response of the 11 substrates added by 23% in the Ouagadougou soil and by 13% in the Tamale soil. N fertilization decreased soil pH in both cities by 1.1 units. However, a pH-H 2 O of 4.7 led to reduced MBC and ergosterol contents at Tamale. Also, the Shannon index of the respiratory response was positively correlated with the soil pH. Clean water irrigation decreased the ergosterol content and increased the respiratory response to organic acids. Conclusions Biochar addition with N fertilization improved habitat conditions for soil microorganisms. An N fertilizer-induced decline in soil pH < 5 should be avoided, as it decreased MBC and microbial functional diversity. Graphical Abstract

To quantify carbon (C) and nitrogen (N) losses in soils of West African urban and peri-urban agriculture (UPA) we measured fluxes of CO2-C, N2O-N, and NH3-N from irrigated fields in Ouagadougou, Burkina Faso, and Tamale, Ghana, under different fertilization and (waste-)water regimes. Compared with the unamended control, application of fertilizers increased average cumulative CO2-C emissions during eight cropping cycles in Ouagadougou by 103% and during seven cropping cycles in Tamale by 42%. Calculated total emissions measured across all cropping cycles reached 14 t C ha(-1)in Ouagadougou, accounting for 73% of the C applied as organic fertilizer over a period of two years at this site, and 9 t C ha(-1)in Tamale. Compared with unamended control plots, fertilizer application increased N2O-N emissions in Ouagadougou during different cropping cycles, ranging from 37 to 360%, while average NH3-N losses increased by 670%. Fertilizer application had no significant effects on N2O-N losses in Tamale. While wastewater irrigation did not significantly enhance CO2-C emissions in Ouagadougou, average CO2-C emissions in Tamale were 71% (1.6 t C ha(-1)) higher on wastewater plots compared with those of the control (0.9 t C ha(-1)). However, no significant effects of wastewater on N2O-N and NH3-N emissions were observed at either location. Although biochar did not affect N2O-N and NH3-N losses, the addition of biochar could contribute to reducing CO2-C emissions from urban garden soils. When related to crop production, CO2-C emissions were higher on control than on fertilized plots, but this was not the case for absolute CO2-C emissions.

Crop yield simulation using the Denitrification–Decomposition (DNDC) model can help to understand key bottlenecks for improved nitrogen (N) use efficiency and estimate greenhouse gas (GHG) emissions in West African urban vegetable production. The DNDC model was successfully calibrated using high-resolution weather records, information on management practices and soils, and measured biomass accumulation and N uptake by amaranth (Amaranthus L.), jute mallow (Corchorus olitorius L.), lettuce (Lactuca sativa L.), and roselle (Hibiscus sabdariffa L.) for different input intensities (May 2014–November 2015) in urban vegetable production of Tamale (N-Ghana, West Africa). The root mean square error (RMSE) and relative error (E) values fell within the confidence interval (a 5%) of the measurements, and there was a high correlation (0.91 to 0.98) between measurements and predictions. However, the analysis of uncertainty and factor importance indicated that soil properties (pH, SOC, and clay content) and weather (precipitation) variability contributed highly to yield uncertainty of vegetable biomass.

With proteomic analysis of activated sludge for landfill leachate treatment a better understanding of the current status of the process could be achieved.

This study reports and analyzes nutrient balances in experimental vegetable production systems of the two West African cities of Tamale (Ghana) and Ouagadougou (Burkina Faso) over a two-year period comprising thirteen and eleven crops, respectively. Nutrient-use efficiency was also calculated. In Tamale and Ouagadougou, up to 2% (8 and 80 kg N ha −1 ) of annually applied fertilizer nitrogen were leached. While biochar application or wastewater irrigation on fertilized plots did not influence N leaching in both cities, P and K leaching, as determined with ion-absorbing resin cartridges, were reduced on biochar-amended plots in Tamale. Annual nutrient balances amounted to +362 kg N ha −1 , +217 kg P ha −1 , and –125 kg K ha −1 in Tamale, while Ouagadougou had balances of up to +692 kg N ha −1 , +166 kg P ha −1 , and –175 kg K ha −1 y −1 . Under farmers' practice of fertilization, agronomic nutrient-use efficiencies were generally higher in Tamale than in Ouagadougou, but declined in both cities during the last season. This was the result of the higher nutrient inputs in Ouagadougou compared to Tamale and relatively lower outputs. The high N and P surpluses and K deficits call for adjustments in local fertilization practices to enhance nutrient-use efficiency and prevent risks of eutrophication.

Urban agriculture in developing countries contributes to food diversity and security of the urban population. Its importance will increase in the future because of fast-growing urbanization. Little is known about nutrient fluxes and balances of these high input agricultural systems, which are characterized by high fertilizer use, often combined with wastewater irrigation. Adding biochar to soil has shown the potential to decrease nutrient leaching, increase yields and nutrient use efficiency. Therefore, we installed lysimeters in a multi-factorial field experimental in Tamale, Northern Ghana. The treatments included a control (no amendments applied), biochar at 20 t ha−1, mineral fertilization according to the farmers’ practice and a combination of biochar amendment and fertilization. All treatments were irrigated with tap water or wastewater. The results show higher water losses under wastewater irrigation (+ 33%). The addition of biochar had no effects on nutrient leaching, balances or water flux. Leaching losses of nitrogen were around 200 kg N ha−1 when irrigation exceeded the crop demands. When irrigation was more appropriate, the leaching rates were 50–100 kg N ha−1. The leaching of Mg and Ca almost doubled in some seasons and negative mass balances under mineral fertilization entailed soil acidification. Nitrogen balances varied strongly depending on the season, irrigation water qualities or fertilization (− 50 to 222 kg NO3-N ha−1). We conclude that the high nutrient load associated with the commonly-practiced wastewater irrigation entails large leaching losses. These cannot be curbed by biochar application and should be accounted for in fertilizer management in urban vegetable production.

Agricultural production needs to increase, particularly in sub-Saharan Africa, many rural people are undernourished, and the urban population is growing rapidly. It is worrisome that on many West African soils with low cation exchange capacity and soil organic carbon content, mineral fertilization is rather inefficient. Under these conditions, wherever available untreated wastewater is used for irrigation despite the potential health risks to producers and consumers. For intensively cultivated soils with high mineralization rates, biochar application has been advocated as a promising management option. However, the agronomic benefits of wastewater reuse in agriculture and its interaction with biochar have received only limited attention. This study therefore investigated the effects of mineral fertilizer application and biochar amendment at two water quality and quantity levels on soil moisture, plant nutrition and biomass production on a Petroplinthic Cambisol over 2 years. Rice husk biochar applied at 20 t ha−1 significantly increased fresh matter yields in the first five cropping cycles by 15%, and by 9% by the end of 2 years. Compared with clean water, wastewater irrigation increased yields 10–20-fold on unfertilized plots during the dry seasons, while a fourfold increment was observed in the wet seasons. This seasonal difference is likely a result of the high sequence of irrigation events during the dry season. In this study, fertigation with wastewater contributed significantly to plant nutrition and nutrient recovery while yield-increasing biochar effects disappeared over time. Soil moisture was enhanced by up to 9% due to biochar amendments under unfertilized conditions.

In West Africa population growth and fast urbanization challenge food security for which urban and peri-urban agriculture plays an increasing role. Adding biochar to soils depleted in soil organic carbon may improve soil quality but its effectiveness in high input systems, such as urban horticulture in West Africa, is unknown. We studied the effects of fertilization, amended biochar from agricultural waste, irrigation water quality and quantity on small-scale urban vegetable production in a multi-factorial split-plot experiment on a Haplic Lixisol in Ouagadougou, Burkina Faso. A single application of corn cob biochar at the rate of 20 t ha−1 was used in a 2-year study covering eleven cropping cycles. Biochar significantly improved total fresh matter yields of two amaranth cycles by 39% and 17%, lettuce by 7% and carrot by 11%. Repeated measures analysis showed that biochar increased average total biomass by 9% and marketable yield by 6%. Biochar was effective on fertilized plots while plant growth on unfertilized plots was limited by nutrients, most likely nitrogen (N). A 33% reduction in irrigation water caused yield declines of 4–23% which was more pronounced in fertilized plots with higher water consumption by the larger plants. Biochar increased potassium (K) concentrations while wastewater reduced phosphorus (P) in plant tissue. The study showed a positive effect of biochar on crop yields and nutrition while wastewater effects were limited to nutrient deficient plots.

In the degradation of ammonia (NH4+) to gaseous nitrogen (N2), the nitrification is one of the two reaction steps. The nitrification itself is divided in two steps and is performed by two different types of bacteria. Current literature has shown that there are types of bacteria, which have the genetic equipment to perform both steps in one bacteria. Nevertheless, in wastewater and landfill leachate treatment, ammonia-oxidizing organisms (AOO) and nitrite-oxidizing organisms (NOO) occur as a symbiosis. The intermediate of the two consecutive reaction steps (NO2-, nitrite) is toxic. For this reason, both steps are necessary for the two bacterial groups. To determine the ratio of AOO, NOO and heterotrophic bacteria (which use organic compounds as carbon and energy source) the oxygen uptake rate (OUR) with selective inhibition with N-allylthiourea (ATU) and azide is used. In the inflow of a pilot plant in one street a step by step increased amount of a process water out of a fermentation plant was added to the landfill leachate. For comparison, the other street was supplied only with landfill leachate with the same amount of nitrogen. As a result, comparable values for the different bacterial groups and reproducible results were measured and lead to a better understanding of the analysed nitrification sludge. Deeper understanding of the behavior of the different groups will result in a reduce risk of malfunctions and a more stable operation in the wastewater or landfill leachate treatment plant.

Pyrolysis of biomass, reduces its volume, mass, odour, and potential pathogens, while concentrating nutrients in the resulting biochar. However, the plant availability of nutrients in particular of nitrogen remains largely unknown. Therefore, we investigated the nutrient availability of carbonized poultry litter. A nutrient poor soil was either fertilized with poultry litter or poultry litter carbonized at 500°C at the rates of 1.5, 3 and 6 t/ha. These organic amendments were compared with corresponding rates of mineral fertilizers (NH4NO3, KCl, CaHPO4, MgSO4) in a pot experiment. After four successive harvests of ryegrass (Lolium sp.) in a greenhouse we analyzed plant nutrient uptake and nutrient concentrations in the soil. While all treatments showed a linear increase in plant growth and nitrogen uptake, the plants fertilized with carbonized poultry litter did not show such a response. The carbonized poultry litter treatment produced more biomass than the unfertilized control, but the tissue concentration of nitrogen was below that of the control. Mehlich 1 extractable nutrients in the soil showed that there is more available phosphorus, potassium, calcium and magnesium in the soil fertilized with the carbonized poultry manure, but these available nutrients were not utilized due to the nitrogen limitation to plant growth. The results clearly show that nitrogen contained in carbonized poultry litter is not available for plants

Adding biochar to nutrient rich organic matter during composting reportedly reduces nitrogen (N) volatilization and carbonization of feedstock stabilized organic carbon (C). We studied the effects of biochar, produced from agricultural residue as compost additives, on CO2, N2O, and NH3 fluxes in northern Ghana. Three biochar types [from corn cobs (cCC), rice husks (cRH), and wood (cWO)] and their uncharred feedstocks (CC, RH, and WO), were co-composted with poultry manure (15 vol.-%) and rice straw (60 vol.-%) in randomly allocated 1 m(3) compost bins. Emissions were measured using a closed chamber system composed of a photo-acoustic infrared gas analyser (INNOVA 1312-5). Biochar amended composts showed higher CO2-C emission rates during the initial composting phase. Maximum CO2-C flux rates during the first week reached 15 g CO2-C m(-2) h(-1) in cRH and 12 g CO2-C m(-2) h(-1) for RH, while those from cCC were 19 g CO2-C m(-2) h(-1) and from CC 14 g CO2-C m(-2) h(-1). Respiration significantly dropped during the last week of composting and lower rates recorded with carbonized compared with the un-carbonized feedstocks. Total CO2-C losses were 12 kg m(-2) 34 d(-1) for RH and 9 kg m(-2) 34 d(-1) for cRH, resulting in a 29% reduction of CO2-C. Emissions were 9 and 10 kg CO2-C m(-2) 34 d(-1) for cCC and CC, while cWO and WO emitted 7 and 8 kg CO2-C m(-2) 34 d(-1), respectively. Volatilization of NH3-N was significantly lower in compost containing cWO (89 g N m(-2) 34 d(-1)) compared to WO (166 g N m(-2) 34 d(-1)), while N2O-N emissions were lower in compost mixtures containing cRH (27%), cCC (7%), and cWO (16%) compared with their un-carbonized feedstock.

Urban agriculture is characterized by fast rotation of cropping cycles and high inputs and outputs on relatively small areas of land. Depletion of soil organic carbon and low nutrient use efficiency are severe agricultural constraints in the sandy soils of West Africa. We hypothesized that such an intensive system would provide ideal preconditions for the use of biochar, that biochar would enhance yields in urban horticulture, and that farmers would be able to produce biochar for on-farm use in Tamale, Ghana. Therefore, we studied the opportunities and challenges of biochar using a semi-participatory research approach. Working with 12 participant farmers, we defined research questions which were relevant to their livelihoods and collected qualitative and observational data, which determined the selection of variables to measure quantitatively. Different quality parameters such as leaf color and stiffness of lettuce were important to farmers and marketers when assessing the agronomic benefits of biochar. By adding biochar to their normal agricultural practice farmers were able to increase lettuce yields by 93%. This remarkable increase might be partially caused by farmers’ improved management of biochar plots: they concentrated their resources where they expected to yield the largest returns. Using a simple top-lit updraft gasifier, a special chimney for rice husk carbonization, it was relatively simple for farmers to produce biochar in the field, with an efficiency of 15–33%. These stoves’ payback times were between 1 and 2 months. Yet, rather than the efficiency of the carbonization technology, often emphasized in biochar research, the availability of feedstock and labor considerations determine the technology selected by farmers for biochar production. This is a novel approach to considering the economic realities of farmers in a semi-participatory appraisal where farmers both produce and apply biochar. This is crucial in order to understand and identify meaningful and economically viable uses of biochar.

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The interrelations between biochar (BC) and soil microbiota remain unclear. Addressing this will be important for understanding how BC affects soil properties and plant growth. Here, we tested the influence of wood-derived BC with immobilised Trichoderma viride on rye Secale cereale L. in sandy soil. We found that the addition of BC leads to a significant (P < .05) increase in the concentrations of Ca2+ and Mg2+, as well as a decrease in the concentration of Al3+, irrespective of BC particle size and the presence of T. viride. Plant growth was stimulated in the presence of small (<2 mm) particle-sized BC. Fungal diversity, as well as an absolute and relative abundance of Trichoderma spp., was tested by cultivation-dependent methods and qPCR. Both of these approaches revealed a positive effect of BC on the survival of Trichoderma spp. under the tested conditions, especially in the presence of a small particle size fraction.

In many water-scarce countries, waste water is used for irrigation which poses a health risk to farmers and consumers. At the same time, it delivers nutrients to the farming systems. In this study, we tested the hypotheses that biochar can be used as a filter medium for waste water treatment to reduce pathogen loads. At the same time, the biochar is becoming enriched with nutrients and therefore can act as a fertilizer for soil amendment. We used biochar as a filter medium for the filtration of raw waste water and compared the agronomic effects of this "filterchar" (FC) and the untreated biochar (BC) in a greenhouse pot trial on spring wheat biomass production on an acidic sandy soil from Niger. The biochar filter showed the same removal of pathogens as a common sand filter (1.4 log units on average). We did not observe a nutrient accumulation in FC compared to untreated BC. Instead, P, Mg and K were reduced during filtration while N content remained unchanged. Nevertheless, higher biomass (Triticum L. Spp.) production in BC (+72%) and FC (+37%) treatments (20 t ha(-1)), compared with the unamended control, were found. There were no significant differences in aboveground biomass production between BC and FC. Soil available P content was increased by BC (+106%) and FC (+52%) application. Besides, mineral nitrogen content was reduced in BC treatemineral nitrogen compounds on FC surfaces. Although the nutrients provided by FC decreased, due to leaching in the filter, it still yielded higher biomass than the unamended control. (C) 2017 Elsevier Ltd. All rightd soil and to a lesser extent when FC was used. This may be explained by reduced sorption affinity for s reserved.

The authors investigated the effects of replacing a portion of a commercial broiler feed with false yam tuber meals on broiler growth performance, feed conversion rate (FCR) and blood parameters. Furthermore, wood charcoal was added at various levels to the meals to explore their potential to attenuate toxic effects. One hundred and sixty-eight 28-day-old healthy female broiler chickens (average initial bodyweight 1081.1 +/- 66.20 g) were randomly assigned to 28 experimental groups (7 dietary treatments, 4 replicates) of six birds each, using a randomized complete block design. Dietary treatments included the control diet (commercial broiler feed) (C), raw false yam tuber meal (RFY) replacing 50 g/kg of the commercial broiler feed, false yam tuber meal soaked in water (SFY) replacing 150 g/kg of the commercial broiler feed, RFY with 30 g/kg and 60 g/kg wood charcoal, and SFY with 30 g/kg and 60 g/kg wood charcoal. Growth performance, feed intake and FCR were assessed over four weeks. At the end of the experiment, blood samples were collected from 21 birds (three from each dietary treatment) to analyse haematological and serum biochemical parameters. Analysis of variance, Kruskal-Wallis tests, and simple regressions were used to evaluate the effects of the meals and charcoal. The results indicated that broilers fed 150 g/kg SFY had a significantly lower growth rate and poorest FCR. Consequently, highest bodyweights were observed for C and RFY diets. Additionally, blood serum proteins were below the references ranges for birds fed SFY, particularly with additional charcoal. In contrast, RFY could be included at 50 g/kg in broiler chicken diets without any adverse effects on their performance and blood (serum) parameters. Anti-nutritional substances contained in SFY at this substitution level are harmful to the birds, irrespective of whether charcoal is added or not. In contrast, RFY could replace commercial feed at the studied level (50 g/kg).