In this episode of In Search of Soil, we have Dr. Johannes Lehmann, one of the leading scientists in the field of soil biogeochemistry. We’ll discuss and question everything we know—or think we know—about humus, biochar, and soil organic matter with insightful, thought-provoking discussions.

Dr. Johannes Lehmann is a professor at Cornell University College of Agriculture and Life Sciences with a profound interest in advancing studies on biogeochemical cycles of carbon and nutrient elements in soil. Apart from pioneering studies on biochar in the 90’s, his current field of research is locally and globally relevant, impacting both climate change and environmental pollution.

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In this episode of In Search of Soil:

• Introduction to today’s guest, Johannes Lehmann (00:46 )
• Johannes Lehmann on our general understanding of organic matter in soil (01:55 )
• The key unknown to hasten our progress to understand soil (06:00 )
  • Finer points that are unknown, mainly the intricate interactions between microorganisms (08:12 )
• The theory of humus and why it made sense (10:20 )
• Humus, as we understand it, does not exist (17:34 )
• The initial thought behind the formation of humus (19:38 )
• In situ: microorganisms, soil, and carbon (20:53 )
• An analogy of functional complexity (25:40 )
• The question of the evolution of soil microorganisms (29:15 )
• Is the lack of microorganismal evolution nature protecting itself? (31:20 )
• The accessibility of carbon and its potential buildup (32:05 )
• The amount of labile carbon vs. the amount of recalcitrant carbon (36:25 )
• What tillage does to the carbon in the soil (38:27 )
• Where the long-term carbon storage in soil happens (41:23 )
• Adding more stored carbon into the soil (44:18 )
• The carbon lost from the soil over the last thousands of years (51:43 )
• Does more microbial population in the soil mean higher CO₂ emissions? (53:19 )
• How much carbon leaks out of a certain farming model (57:40 )
• How beneficial is biochar to carbon sequestration? (01:00:52 )
• Justifying the cost of using biochar (01:09:25 )
• The possibility of positive plant growth results with the use of biochar (01:18:42 )
• Thinking about whether to compost or make biochar out of manure (01:23:08 )
• Does pyrolyzing manure break down persistent herbicides?  (01:29:32 )
• Organic matter, water-holding capacity, and context (01:31:17 )
• The value of carbon left after mineralization (01:36:45 )
• Microbial and abiotic nitrogen cycles (01:38:32 )
• The ammonia gas in the soil (01:43:22 )
• Where to keep up-to-date with current research and all things biochar (01:44:35 )