In this episode of In Search of Soil, we’re talking to soil scientist Dr. Kurt Spokas of the United States Department of Agriculture to walk us through what biochar is, what it can potentially do, and what its limitations are when it comes to applying it to agricultural production.

Dr. Kurt Spokas is a soil scientist at the United States Department of Agriculture who has dedicated years of research on the impact of farming practices on the cycling of carbon, nitrogen, and other greenhouse gases, including transport and surface exchange of greenhouse gases. His areas of interest include biogeochemistry, contaminant hydrology and water quality, and soil physics.

Dr. Spokas' Publications: https://www.ars.usda.gov/midwest-area/stpaul/swmr/people/kurt-spokas/publications/

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In this episode of In Search of Soil

• Any changes in what we know about biochar in the last 10 years? (01:42)
• Questions that still remain around biochar (02:20)
• Why we can’t yet answer how biochar works (02:51)
• Biochar: a positive, a negative, or neither? (04:48)
• Potential negatives of biochar that can possibly hinder plant growth (05:56)
• Dr. Kurt Spokas’ research on biochar on the nitrogen cycle (08:05)
• Biochar to potentially mitigate nitrous oxide emissions (09:24)
• The variability between biochars (10:27)
  • The differences and nuances of variability between biochars (12:36)
• Variably defined biochars in different studies (13:18)
• Aged biochars (14:50)
• What changes are happening in a biochar undergoing oxidation? (16:26)
• Biochar for agriculture before completely understanding what it is and what it does (18:08)
• No two biochars are the same (19:57)
• Is there a sweet spot for feedstock materials to use as biochar? (20:55)
• Silica deficiency in soils (22:53)
  • Silica entering the soil (23:32)
• Scientific knowns when it comes to biochar (24:06)
  • Biochar’s potential as construction material (26:30)
• Can you use biochar as a substitute in a potting mix? (27:20)
• Can a small amount of biochar make a difference? (28:16)
• Is more biochar better than less biochar? (30:07)
• Adding the bio to the char to become biochar (30:44)
• Why nutrients attach to biochars (32:32)
• Surface area of organic matter vs. surface area of biochar (34:15)
• How long can the carbon in biochar sit in the soil? (35:40)
  • What makes the carbon in biochar unique (37:05)
• Gradual breaking down of carbon over time (39:06)
• Adding carbon now via biochar is adding carbon later (40:33)
• Biochar and beneficial agricultural microbial groups (41:42)
• Amazonian soils, Terra Preta, and biochar (42:48)
  • Was adding charcoal to the soil actually intentional? (46:40)
  • Can we say the char actually made the soils better? (48:03)
• Higher microbial populations, slower carbon turnover (49:49)
• The microbe population that appears high in Terra Preta soils (52:47)
• To add or not to add biochar to your farmland? (53:33)
• Potential negative to adding biochar (54:52)
• A key piece of information to quantifying biochar and its effects (56:22)
• Reproducibility of activated carbon products (57:46)
• Pushing the science of biochar forward (01:00:07)
• Homemade biochars (01:01:36)
• Biochars and potential toxins such a heavy metals and toxic organic compounds (01:04:01)
• For farmers: some takeaways about biochar (01:07:06)
• Where to find more information on biochar, its application, etc. (01:08:32)
• Where to find Dr. Kurt Spokas and his work (01:10:18)