Factors to consider if choosing biochar as a soil amendment
The concern about climate change and its mitigation has led to the consideration of myriad soil amendments that can be used to address this issue. One such soil amendment is biochar, or the resulting product from pyrolysis of organic waste materials. See the White Paper on this website for a detailed discussion of the biochar topic.
An article titled “A global synthesis of biochar’s sustainability in climate-smart agriculture–evidence from field and laboratory experiments” by Huang et al. appears in the journal “Renewable and Sustainable Energy Reviews” (Vol. 172, Feb. 2023, 113042). The contents of this article highlight the effects of biochar in field experiments. Major points from that article follow.
• Results from 592 papers published before 2021 that reported greenhouse gase (GHG) emissions, soil carbon (C) stock, crop yields, and soil nitrogen (N) loss resulted in a dataset that had 9970 observations for the subject variables.
• Research reported in the articles was conducted on cropland soils.
• The biochar in the studies was produced by pyrolyzing organic materials.
• Overall, crop yield response from soils with biochar addition were positive, but were greater in laboratory experiments (25.4% increase) vs. field experiments (15.7% increase). Similar patterns were noted for soil organic carbon (SOC) and total N.
• Generally, addition of biochar to soil reduced methane (CH4) and nitrous oxide (N2O) emissions in both lab and field experiments.
• The effects of biochar application on crop yield, SOC, GHG emissions, and N dynamics depended on multiple factors that included biochar properties and application methods, soil properties, climate, and agronomic management factors such as tillage, irrigation, fertilization, and residue addition.
• Biochar feedstock had a major effect on crop yield, with manure-based biochar increasing yield the most, followed by herbaceous-based biochar. The effect of feedstock type was greater in lab than in field experiments.
• Positive crop yield responses increased with increasing biochar application rates, and peaked at rates between 9 and 18 tons/acre in field experiments.
• Biochar’s positive effect on crop yield was more pronounced in fine-textured vs. coarse-textured soils in field experiments.
• In field experiments, biochar’s positive effect on SOC was less in soils with a higher/increasing C content.
• N fertilizer did not affect biochar’s effect on crop yield, carbon dioxide (CO2) and N2O emissions, or nitrate (NO3) leaching in field experiments.
• The results of this meta-analysis showed that biochar addition to soil can increase SOC pools and crop yield.
• These results also show that the positive effects from biochar addition to soil are greater in lab vs. field experiments, and that biochar application rates in lab experiments were often unrealistically high. Thus, results from lab experiments with biochar likely lead to an over-estimation of the positive effects of biochar.
• Overall, the findings from this meta-analysis lead to the following conclusions. 1) Data derived from field experiments should be used when analyzing the effects of biochar on crop yield, soil properties, and GHG emissions. 2) Unrealistically high biochar application rates used in lab experiments are likely impractical under field conditions because of the high cost of feedstock pyrolysis, and transportation of the resulting product to the site of its application. 3) Long-term field experiments should be used to determine the legacy effects of biochar soil amendment on crop yield, soil properties, and GHG emissions. 4) The costs associated with biochar production and its application to field sites, plus the potential impact of the chosen biochar product on crop yield, should always be considered and verified before deciding to use biochar as a soil amendment. 5) There should be a determination of the cost for production of biochar from available organic waste materials such as poultry litter that are available in the Midsouth, and if in fact there is a potential market in the region for these biochar products if the facilities needed for their production are constructed.
Composed by Larry G. Heatherly, Mar. 2023, larryh91746@gmail.com