Carbon Abatement and Emissions Associated with the Gasification of Walnut Shells for Bioenergy and Biochar Production

By converting biomass residue to biochar, we could generate power cleanly and sequester carbon resulting in overall greenhouse gas emissions (GHG) savings when compared to typical fossil fuel usage and waste disposal. We estimated the carbon dioxide (CO2) abatements and emissions associated to the concurrent production of bioenergy and biochar through biomass gasification in an organic walnut farm and processing facility in California, USA. We accounted for (i) avoided-CO2 emissions from displaced grid electricity by bioenergy; (ii) CO2 emissions from farm machinery used for soil amendment of biochar; (iii) CO2 sequestered in the soil through stable biochar-C; and (iv) direct CO2 and nitrous oxide (N2O) emissions from soil. The objective of these assessments was to pinpoint where the largest C offsets can be expected in the bioenergy-biochar chain. We found that energy production from gasification resulted in 91.8% of total C offsets, followed by stable biochar-C (8.2% of total C sinks), offsetting a total of 107.7 kg CO2-C eq Mg-1 feedstock. At the field scale, we monitored gas fluxes from soils for 29 months (180 individual observations) following field management and precipitation events in addition to weekly measurements within three growing seasons and two tree dormancy periods. We compared four treatments: control, biochar, compost, and biochar combined with compost. Biochar alone or in combination with compost did not alter total N2O and CO2 emissions from soils, indicating that under the conditions of this study, biochar-prompted C offsets may not be expected from the mitigation of direct soil GHG emissions. However, this study revealed a case where a large environmental benefit was given by the waste-to-bioenergy treatment, addressing farm level challenges such as waste management, renewable energy generation, and C sequestration

A Comprehensive Method for Fractionating Soil Organic Matter Not Protected and Protected from Decomposition by Physical and Chemical Mechanisms

The objective of this work was to describe a method for isolating meaningful and measurable soil organic matter (SOM) pools that differ in the mechanisms by which they are protected from decomposition. The proposed method is appropriate for soil C stabilization and sequestration studies. Unlike previous fractionation schemes, this procedure allows free SOM located between aggregates (unprotected C pool) and SOM occluded within both macroaggregates and microaggregates (C weakly and strongly protected by physical mechanisms, respectively) to be recovered separately, freed from the soil mineral matrix and the mineral-associated SOM pool (C pool protected by chemical mechanisms) and thus well suited to advanced chemical characterization by 13C-NMR. Briefly, free SOM is isolated by an initial density separation. Stable macroaggregates are broken up into stable microaggregates and intra-macroaggregate SOM, which is then separated by density. Finally, intra-microaggregate SOM is isolated from mineral-associated SOM by a third density separation after ultrasonic disruption. The SOM dissolved during the fractionation procedure is also recovered. Results obtained on soil samples with contrasting textures suggested that clay content induces a decrease of the proportion of free organic C and an increase of mineral-associated organic C content. Free SOM is characterized by a marked presence of undecayed organic material and biologically labile substances, such as carbohydrates and proteins. In contrast, SOM occluded within aggregates, especially within microaggregates, represents a more decomposed fraction, relatively enriched in unsubstituted-aliphatic material, most probably lipid biopolymers

A participatory assessment of nitrified urine fertilizer use in Swayimane, South Africa: Crop production potential, farmer attitudes and smallholder challenges

Long-term nutrient mining of soil hampers agricultural production across Africa. However, emerging sanitation technologies afford a hygienically safe and ecologically sustainable solution to this development challenge by providing fertilizers derived from human excreta that could facilitate a socio-technical transition toward a more sustainable food system. To evaluate one such technology, nitrified urine fertilizer (NUF), we conducted participatory action research to assess the potential, from both a biophysical and social perspective, of NUF to serve as a soil fertilizer to support smallholder agricultural production in Swayimane, South Africa. To achieve this objective, we formed a stakeholder group comprised of a cooperative of smallholder farmers, a local NGO (Zimele), and researchers from ETH Zurich and the University of Kwazulu-Natal. Over the course of two growing seasons (2016 and 2017) this stakeholder group assessed the potential of NUF to support smallholder vegetable production (i.e., cabbage). First, we adopted a randomized complete block design incorporating five treatments in season 1 (unfertilized control, nitrified urine, nitrified urine+bone meal, urea, and urea+diammonium phosphate (DAP) and six treatments (unfertilized control, urea, urea+DAP, DAP, nitrified urine, and nitrified urine+DAP) in season 2 to assess cabbage yield and leaf nutrient concentration (sodium, phosphorus, potassium, carbon, nitrogen). Although we observed large variability in yields, the urine-based treatments were as effective as any of the chemical fertilizers. Second, beyond the biophysical analysis, we elicited the challenges and opportunities of the smallholder farmers in our stakeholder group, as well as their attitudes toward the use of NUF as a fertilizer. Through this qualitative work, farmers indicated that their attitudes about the use of NUF as a fertilizer improved and that they would be willing to incorporate this product into their production practices if it was available at scale. Thus, we demonstrate the potential of participatory action research to co-produce knowledge and awareness around an innovative technology. In so doing, we provide evidence that this approach can support a change toward nutrient recycling-based agriculture

Effects of Biochar Production Methods and Biomass Types on Lead Removal from Aqueous Solution

Biochar has proven its potential in removing heavy metal ions from water. The objective of this study was to evaluate locally obtained biomass feedstocks for biochar production and their efficiency as a sorbent for aqueous lead (Pb2+) removal. The biomass feedstocks consisted of avocado seed, avocado peel, grapefruit peel, and brown seaweed, which represent agricultural and marine biomasses. The biochar materials were produced in two different methods: (1) a laboratory tube furnace at 300 °C and (2) a Do-It-Yourself (DIY) biochar maker, “BioCharlie Log”. The biochars were characterized for selected physicochemical properties, and batch adsorption tests with 10 mg Pb2+ L−1 were conducted. All biochars exhibited \u3e90% Pb2+ removal with the avocado seed and grapefruit peel biochars being the most effective (99%) from the tube-furnace-produced biochars. BioCharlie-produced-biochars showed similar Pb2+ removal (90–97%) with brown seaweed and avocado seed biochars being the most effective (97%). Land-based biochars showed a higher carbon content (\u3e53%) than the brown seaweed biochar (28%), which showed the highest ash content (68%). Our results suggested that oxygen-containing surface functional groups in land-based biochar and mineral (ash) fraction in marine-based biochar play a key role in Pb2+ removal. View Full-Tex

Identifying available resources and agricultural practices useful in soil fertility management to support orange-fleshed sweet potato cultivation on smallholder farms in Mozambique

Orange-fleshed sweet potato is an important source of macro-and micronutrients for humans, particularly in resource-poor rural communities. However, sweet potato cultivation removes large amounts of nutrients from the soil. Hence, soil fertility replenishment is vital to secure long-term food production. The lack of access to fertilizers hinders the ability of farmers to supply and replenish soil nutrients, intensifying food insecurity. This study aimed at identifying locally available organic residues and agricultural practices with potential application in soil fertility management to prevent soil degradation in southern Mozambique. We conducted a survey to gather information on the farmers’ demographics and farming systems of 107 orange-fleshed sweet potato farmers. Results show that more than 70% of farmers use agroecological practices such as intercropping and crop rotation, and more than 90% indicated having residual crop biomass after harvest. Most cultivated crops, such as lettuce, beans, etc., are harvested in July-August, before the start of orange-fleshed sweet potato cultivation. Thus, there is potential for the application of crop residues as an organic amendment for orange-fleshed sweet potato cultivation. Nevertheless, farmers need support to adopt soil fertility management based on locally accessible resources, therefore ensuring extension services focused on the long-term benefits of sustainable practices are vital

Biochar Enhances Nitrous Oxide Reduction in Acidic but Not in Near-Neutral pH Soil

We quantified nitrous oxide (N2O) fluxes and total denitrification (N2O + N2) in an acidic (Ferralsol) and a near-neutral pH soil (Cambisol) to determine whether biochar’s alkalinization effect could be the mechanism inducing potential reductions in N2O fluxes. In Ferralsol, decreases in N2O emissions and in the N2O to N2O + N2 ratio were observed in both biochar and lime treatments. In Cambisol, neither biochar nor lime decreased N2O emissions, despite significantly increasing soil pH. The abundance and community structure of nosZ gene-bearing microorganisms indicated that gene abundances did not explain biochar effects, but a higher diversity of nosZ gene-bearing microorganisms correlated to lower total denitrification. Overall, our results suggest that biochar’s potential to decrease N2O emissions, through soil alkalinization, may be more effective in acidic soils

Post-Harvest Eucalyptus Residue Removal Reduces Soil Aggregation and Biological Activities in Central-West Brazil

Tree residue removal from Eucalyptus plantations after timber harvest can reduce soil functioning by reducing the organic matter input. To assess the effects of residue management systems (RMS) on soil aggregation, carbon (C) and nitrogen (N) content, and biological activities, a field trial was conducted in a commercial Eucalyptus plantation (loamy sand soil) in Mato Grosso do Sul, Brazil. The study assessed three RMS: cut-to-length (CTL), tree-length (TL), and bare litter (BL), respectively. After 21 months, undisturbed soil samples were collected and physically isolated into three aggregate-size fractions: large macroaggregates (LM), medium macroaggregates (SM), and microaggregates (MI). Results showed that these soils are mostly composed of LM (54%), and that removing harvest residues from the growing site included total organic carbon (TOC) by 28%, microbial biomass-C by 20%, fluorescein diacetate hydrolysis by 17%, and β-glucosidase activity by 26%, when compared to CTL. TL outperformed CTL for the proportion of LM and LM-associated TOC. Across fractions, a higher microbial quotient was observed in SM and MI fractions, suggesting that the TOC has higher stability inside the LM. This study suggests that leaving harvest residues on the soil should be recommended for Eucalyptus plantations, especially in low-fertility sandy soils, as it helps in maintaining the soil structure and biological activities critical for soil health and ecosystem function

Soil nitrogen transformations under elevated atmospheric CO2 and O3 during the soybean growing season

We investigated the influence of elevated CO2 and O3 on soil N cycling within the soybean growing season and across soil environments (i.e., rhizosphere and bulk soil) at the Soybean Free Air Concentration Enrichment (SoyFACE) experiment in Illinois, USA. Elevated O3 decreased soil mineral N likely through a reduction in plant material input and increased denitrification, which was evidenced by the greater abundance of the denitrifier gene nosZ. Elevated CO2 did not alter the parameters evaluated and both elevated CO2 and O3 showed no interactive effects on nitrifier and denitrifier abundance, nor on total and mineral N concentrations. These results indicate that elevated CO2 may have limited effects on N transformations in soybean agroecosystems. However, elevated O3 can lead to a decrease in soil N availability in both bulk and rhizosphere soils, and this likely also affects ecosystem productivity by reducing the mineralization rates of plant-derived residues

Biomass residues improve soil chemical and biological properties reestablishing native species in an exposed subsoil in Brazilian Cerrado

Revegetation of exposed sub-soil, while a desirable strategy in the recovery processes, often fails due to extreme soil chemical properties, such as low organic matter and pH levels inhospitable to biological activities such as nutrients cycling and plant establishment. This is the case for approximately 800 ha of the Cerrado biome in Brazil, where erecting the embankment of a hydroelectric dam in the 1960’s stripped vegetation, soil, and subsoil layers thereby distorting the soil properties. This work evaluates the effectiveness of restoration management (RM) treatments, to restore the soil quality, including biological activity and chemical attributes. In a factorial scheme, RM treatments include the addition of organic residue from aquatic macrophytes (AM) at 3 rates (0, 16 and 32 t ha-1), combined with ash from sugar cane bagasse of agroindustrial origin (BA) at 4 rates (0, 15, 30 and 45 t ha-1). RM samples contrasted samples collected from undisturbed Cerrado (CER) as well as a degraded area without intervention (DAWI). The mechanized RM plots received amendments and reforestation of 10 Cerrado native tree species. After 5 years, vegetation covered up to 60% of the surface in RM treatments receiving AM32 + BA45. AM and BA residues promoted height increases in the introduced plants. All RM treatments promoted lower levels of Al3+ than DAWI and CER. The combination of AM32 over the rates of incorporated ash increased soil pH and K values similarly to CER. Microbial-related variables, such as microbial biomass-C was the largest in CER, followed by the RM treatments, and the lowest in DAWI. The microbial quotient was no different between CER and RM treatments. The addition of residues such as AM and BA increased the vegetation covered, improved chemical and microbiological indicators. Thus, the residues used aided the recovery process of intensely degraded soils in the Cerrado area