What is the potential for biogas digesters to improve soil fertility and crop production in Sub-Saharan Africa?

Jo Smith, Assefa Abegaz, Robin B. Matthews, Madhu Subedi, Egil R. Orskov, Vianney Tumwesige, Pete Smith

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Abstract

Three alternative soil amendments of organic wastes are considered: application of untreated animal manures, bioslurry from biogas digestion, composted materials, and biochar produced by pyrolysis cook-stoves. Application of untreated manures provides high input of available nutrients, which results in an initial flush in crop growth. However, risks of losing nutrients are high because manure is usually applied before sowing to avoid reduced yields due to phytotoxicity, resulting in increased losses by leaching or volatilization. Furthermore, the heterogeneous nature of untreated manures results in immobilization of nutrients by carbon-rich materials. A greater amount of nutrients are potentially available to crops from applied bioslurry. Typically 5-10% of the nitrogen is lost during anaerobic digestion, but bioslurry provides immediately available nutrients that can be applied as needed, so reducing risks of nutrient loss. If, however, bioslurry was applied in a single dose, losses would be similar in magnitude to untreated manures. Risks of nutrient losses are also lower when wastes are applied as composts, but in contrast to bioslurry, this is because the concentration of immediately available nutrients is very low, most nutrients being held in organic form that will become available only slowly over the growing season. Composts provide an option for single dose application, but a larger proportion of nitrogen is lost during composting (26-51%) than during anaerobic digestion (5-10%). Losses of nitrogen during pyrolysis are also very high (70-90%), but biochar can reduce losses of native soil nutrients by providing exchange sites that hold nutrients in the soil.
Original languageEnglish
Pages (from-to)58-72
Number of pages15
JournalBiomass & Bioenergy
Volume70
Early online date21 Mar 2014
DOIs
Publication statusPublished - Nov 2014

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Biogas
biogas
Sub-Saharan Africa
crop production
soil fertility
Nutrients
Crops
Soils
nutrient
nutrients
manure
Manures
animal manures
nutrient loss
biochar
anaerobic digestion
pyrolysis
compost
Anaerobic digestion
nitrogen

Keywords

  • biogas
  • soil fertility
  • crop production
  • Sub-Saharan Africa
  • anaerobic digestion

Cite this

What is the potential for biogas digesters to improve soil fertility and crop production in Sub-Saharan Africa? / Smith, Jo; Abegaz, Assefa; Matthews, Robin B.; Subedi, Madhu; Orskov, Egil R.; Tumwesige, Vianney; Smith, Pete.

In: Biomass & Bioenergy, Vol. 70, 11.2014, p. 58-72.

Research output: Contribution to journalArticle

Smith, Jo ; Abegaz, Assefa ; Matthews, Robin B. ; Subedi, Madhu ; Orskov, Egil R. ; Tumwesige, Vianney ; Smith, Pete. / What is the potential for biogas digesters to improve soil fertility and crop production in Sub-Saharan Africa?. In: Biomass & Bioenergy. 2014 ; Vol. 70. pp. 58-72.
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abstract = "Three alternative soil amendments of organic wastes are considered: application of untreated animal manures, bioslurry from biogas digestion, composted materials, and biochar produced by pyrolysis cook-stoves. Application of untreated manures provides high input of available nutrients, which results in an initial flush in crop growth. However, risks of losing nutrients are high because manure is usually applied before sowing to avoid reduced yields due to phytotoxicity, resulting in increased losses by leaching or volatilization. Furthermore, the heterogeneous nature of untreated manures results in immobilization of nutrients by carbon-rich materials. A greater amount of nutrients are potentially available to crops from applied bioslurry. Typically 5-10{\%} of the nitrogen is lost during anaerobic digestion, but bioslurry provides immediately available nutrients that can be applied as needed, so reducing risks of nutrient loss. If, however, bioslurry was applied in a single dose, losses would be similar in magnitude to untreated manures. Risks of nutrient losses are also lower when wastes are applied as composts, but in contrast to bioslurry, this is because the concentration of immediately available nutrients is very low, most nutrients being held in organic form that will become available only slowly over the growing season. Composts provide an option for single dose application, but a larger proportion of nitrogen is lost during composting (26-51{\%}) than during anaerobic digestion (5-10{\%}). Losses of nitrogen during pyrolysis are also very high (70-90{\%}), but biochar can reduce losses of native soil nutrients by providing exchange sites that hold nutrients in the soil.",
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