Browsing by Author "Shaw, Liz"

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    Data - Immobilisation of anaerobic digestate supplied nitrogen into soil microbial biomass is dependent on lability of high organic carbon mat
    (Cranfield University, 2024-03-11 09:09) van Midden, Christina; Harris, Jim A.; Shaw, Liz; Sizmur, Tom; Morgan, Hayden; Pawlett, Mark
    Research data for a 150 day incubation study to determine the effects of mixing high organic carbon materials into anaerobic digestate on soil microbial immobilisation of digestate supplied nitrogen and on soil microbial communities. This dateset contains raw data on microbial biomass carbon and nitrogen, soil available nitrogen (ammonium-N and total oxides of nitrate-nitrite), total soil nitrogen, and PLFA biomarkers.
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    Glycerol immobilises anaerobic digestate supplied nitrogen
    (Springer, 2025-01-01) van Midden, Christina; Shaw, Liz; Harris, Jim A.; Sizmur, Tom; Morgan, Hayden; Pawlett, Mark
    Anaerobic digestate, a nutrient rich by-product of the biogas industry, is frequently applied to agricultural land as a fertiliser. However, nitrogen losses from its application negatively impact air and water quality. Therefore, methods are needed to reduce these losses. The aim of this study was to test the efficacy of applying digestate with glycerol, an organic carbon rich by-product of the biodiesel industry, on microbial nitrogen immobilisation and the soil microbial community. Soil was incubated with digestate, applied at a rate equivalent to 250 kg-N ha-1, in a laboratory experiment over 50 days with glycerol additions at either 0, 12, 24 or 36 kg-C m3 of digestate. The addition of glycerol resulted in significantly higher microbial biomass carbon and increased the relative abundance of Gram-negative bacteria. The 24 and 36 kg-C m3 doses of glycerol resulted in similarly greater and longer lasting effect on microbial biomass carbon, indicating that beyond 24 kg-C m3 digestate that nitrogen (or other essential nutrients) became the limiting factor for microbial growth instead of carbon. Soil available nitrogen decreased throughout the study and remained at lower concentrations in glycerol treatments than the digestate only treatment by the end of the study. These results demonstrate that glycerol has the potential to reduce nitrogen losses from digestate application by immobilising nitrogen in the microbial biomass. Therefore, the co-application of digestate and glycerol to soil is a potential mechanism for the biogas and biofuel industries to valorise their respective by-products. Further research is needed to verify that this method is viable under field conditions.
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    Immobilisation of anaerobic digestate supplied nitrogen into soil microbial biomass is dependent on lability of high organic carbon materials additives
    (Frontiers, 2024-03-22) van Midden, Christina; Harris, Jim A.; Shaw, Liz; Sizmur, Tom; Morgan, Hayden; Pawlett, Mark
    Anaerobic digestate is a nutrient rich slurry by-product derived from biogas production, often used as a fertiliser due to its high nitrogen content. However, nitrogen losses from its application can lead to environmental pollution. In a laboratory experiment, the addition of high organic carbon materials to digestate-amended soil as a potential means to stimulate microbial immobilisation of digestate supplied nitrogen was investigated. Soil was incubated in pots for 5 months with digestate (equivalent to 250 kgN ha−1). The impact of adding carbon into the digestate (equivalent to 540 kgC ha−1) as either glycerol, straw, woodchip, or biochar on soil microbial and chemical parameters was quantified. Glycerol amended soils had significantly higher microbial biomass compared to digestate alone during the first month and at 30 days after application had a 4x higher on average microbial N. The digestate + straw treatment resulted in a 2.5x significantly greater nitrogen immobilisation compared to digestate alone after 3 months of incubation. The digestate + woodchip had a 2× higher mean microbial N after 5 months, whilst the biochar amendment did not stimulate significant nitrogen immobilisation at any time. These results suggest that mixing a labile to moderately labile organic carbon amendment, such as straw, with digestate has the greatest potential to reduce nitrogen losses following digestate application through microbial immobilisation.
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    The impact of anaerobic digestate on soil life: a review
    (Elsevier, 2023-07-18) van Midden, Christina; Harris, Jim A.; Shaw, Liz; Sizmur, Tom; Pawlett, Mark
    Using organic amendments to fertilise crops is a crucial part in the sustainability of agricultural systems. The residual slurry remaining after biogas production (anaerobic digestate) contains a rich source of plant nutrients that provides an alternative to mineral fertilisers. The delivery of many nutrients to plants is facilitated by a healthy soil biota: free-living and symbiotic microflora (e.g. archaea, bacteria and fungi) mineralize, solubilize and facilitate plant uptake of nutrients and the soil fauna (e.g. protozoa, microarthopods and earthworms) influence nutrient cycling processes as higher-level consumers and litter transformers. The delivery of nutrients to plants via the activity of this soil food web is influenced by fertiliser inputs. Here we review the impact of anaerobic digestate on soil biota. The quantity and composition of the carbon in digestate has a large influence on soil heterotrophic microbial dynamics and their subsequent influence on nutrient bioavailability. The main points are (1) digestate low in carbon has little effect on soil microorganisms, whereas digestate higher in carbon increases soil microbial abundance and diversity; (2) labile carbon stimulates fast-growing bacteria, whereas recalcitrant carbon shifts the microbial community in favour of slower-growing fungi and Gram-positive bacteria; and (3) earthworms, springtails and nematodes dwelling in the soil surface layer can be negatively affected by digestate application due to toxicity when compounds such as ammonia are present in high concentrations. Generalized understanding of the effect by digestates on soil biota is made difficult by differences in digestate properties caused by varying feedstock and production methods and the inherent heterogeneity of soil. There is a lack of research investigating the impact of repeated digestate application on soil biota and subsequently soil health. This information would give end users more confidence to substitute mineral fertilisers with digestate.
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    Using high organic carbon materials to manipulate soil microbiology for improved nitrogen bioavailability from anaerobic digestate
    (Cranfield University, 2024-09) Van Midden, Christina; Pawlett, Mark; Harris, Jim A.; Sizmur, Tom; Shaw, Liz; Biotechnology and Biological (BBSRC)
    Anaerobic digestate is a by-product of biogas production, often used as a fertiliser due to its high nitrogen content. However, nitrogen losses from its application leads to environmental pollution. The aim of this PhD project was to add agronomic value to anaerobic digestate and reduce its environmental impact by understanding the microbial mechanisms associated with improving its nutrient use efficiency by crops. Digestate with a high organic carbon content is known to stimulate microbial growth and the immobilisation of nitrogen into soil microorganisms. However, after phase separation the liquid fraction contains large quantities of nitrogen in bioavailable forms but has reduced organic carbon. Soil incubation experiments were designed to determine the type (i.e. labile or recalcitrant) and rate of organic carbon required to stimulate microbial immobilisation of nitrogen from liquid digestate. A polytunnel pot experiment with spring barley and a field experiment with sugar beet tested the addition of two carbon additives (straw and glycerol) selected from the previous experiments on plant growth and nitrogen use efficiency. The addition of glycerol increased microbial biomass carbon within a month from application in both experiments, however there was no subsequent increase in crop yield or nitrogen uptake, nor were N2O emissions and ammonia volatilisation affected. This indicates that either the carbon rate was too low to stimulate a nitrogen immobilisation that was significant enough to impact crop nitrogen uptake or that nitrogen remineralised too rapidly to be of benefit to later key nitrogen demanding crop growth stages. Future studies need to focus on determining the optimal amount of carbon to add with digestate to positively impact yield and reduce nitrogen losses. In conclusion this PhD thesis demonstrated a proof of concept that materials high in organic carbon content can be used to temporally immobilise digestate supplied nitrogen within the soil microbial biomass.