Effects of biochar on rhizosphere processes and biochar co-application with nitrification inhibitor on GHG emissions and microbial and enzymatic activities

• Author / Creator

  Pokharel, Prem

• Production of biochar and its use has a wide implication in waste management, climate change mitigation, soil health enhancement and energy production. The strategy to produce biochar and its application to soil aims to replace waste biomass (by-product of photosynthesis) in soil in a stabilized C form which would otherwise be degraded easily and returned to the atmosphere as CO2. Pyrolyzing of waste into biochar and putting that into soil plays significant role in mitigating climate change through reduction in greenhouse gas (GHG) emissions from soil and building up of soil organic carbon (SOC). Biochar is a heterogenous material resulting from varieties of feedstocks, pyrolysis conditions and pre-and post-pyrolysis modifications. Understanding of its effects on soil processes and functions across soil types is important as different biochars behave differently with land use types, soil properties, geographical locations and management practices. Despite having a high opportunity of using biochar in forest, grassland and agricultural land in the Canadian prairie region, the inclusion of biochar in the management practices is meagre because of lack of data to demonstrate the benefits of biochar application in different land use types in this region. So, the main objective of this research was to explore the benefits of biochar application in some of the soil types of this region taking an account of rhizosphere processes, and its interaction with nitrification inhibitor on GHG emissions, microbial and enzymatic activities, nutrient mineralization and crop production.
  The results of the first study demonstrated that biochar produced from pine sawdust decreased carbon dioxide (CO2) emission and global warming potential of the emissions from forest but not from grassland soil. Pine sawdust biochar decreased nitrous oxide (N2O) emission from both forest and grassland soils with no significant effect on methane emissions. Biochar pyrolyzed at 550 °C was more effective than at 300 °C in reducing GHG emissions while post pyrolysis modification by steam activation did not produce significant change in GHG emissions despite having different biochar properties in steam-activated biochar as compared to non-activated one. Second study showed that biochars made from manure pellet and woodchips decreased soil respiration in the rhizosphere (a region of close vicinity to roots) but not from bulk soil. Manure pellet biochars decreased microbial biomass carbon despite increase in dissolved organic carbon and nitrogen. Manure pellet and its biochar had a positive, but woodchips and its biochar had a negative effect on crop production. Third study assessed N transformation using 15N isotope labelling in the rhizosphere and bulk soils after biochar amendment and demonstrated that net N mineralization rates were greater in the biochar amended rhizosphere than bulk soil. Biochar had contrasting effects on gross nitrification rates between rhizosphere and bulk soil and the research demonstrated the importance of gross N transformation processes in understanding the rhizosphere-biochar interactions.
  The fourth and fifth studies assessed the interactions between biochar and nitrapyrin (a commonly used nitrification inhibitor) in affecting nitrification rates, N2O emissions, microbial and ecoenzymatic activities. Manure pellet biochar significantly interacted with nitrapyrin and reduced the efficacy of nitrapyrin in lowering nitrification rates and N2O emissions. Manure compost biochar increased microbial biomass and C-, N- and P- cycling enzymes while nitrapyrin decreased N- and P-cycling enzymes with no significant interaction between manure compost biochar and nitrapyrin in any of the soil processes studied. The sixth study assessed overall effects of biochar in soil microbial biomass and enzymatic activities across biochar and soil factors from the secondary data using meta-analysis technique and demonstrated that biochar was more effective in acidic soil and with low organic matter and finer textured soil for enhancing microbial activities. Biochars produced at a temperature lower than 550 °C, with pH >10 and C/N ratio less than 10 produced the highest impact on increasing soil microbial and enzymatic activities.
  Overall, biochar is beneficial in decreasing GHG emissions, increasing crop production and nutrient limitations for microbial growth and plant uptake in the Canadian prairie region. Its potential in improving soil health was also demonstrated by the increased microbial and enzymatic activities in some of the soils studied. However, the extent of the impact of biochar varied with the feedstock used in pyrolysis, rates of biochar used, land use types and its interaction with other management practices such as nitrification inhibitors. Future research should account for life cycle assessment of biochar production and its application to forest, grassland and agricultural land to determine economic feasibility that will be supportive to farmers interested in using biochar in their management practices in this region.

• Subjects / Keywords

  • Biochar
  • GHG
  • Soil enzyme
  • Ecological stoichiometry
  • Meta analysis
  • Rhizosphere processes
  • Nitrification inhibitor

• Graduation date

  Spring 2023

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-q42w-zm72

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.