Biochar retains all the networks of fluid carrying vessels found in the original plant material. That gives it an incredible amount of surface area compared to the volume. Plus it has a slight electrical charge which attracts to it both water and nutrients, allowing it to store those elements for later use.
Most of the organisms that give soil life are really tiny. A horse needs 1-2 acres of good pasture. That’s as much as half a ton of livestock per acre above ground. But that same acre could contain many horse’s weight of other life forms that live below the surface: a teaspoon of pasture soil could have a billion bacteria, a million fungi, thousands of amoebae. Organic material is broken down over time and consumed by these soil organisms. The microorganisms that break down plant material don’t break down charcoal. Instead they live in it. And they share. Mycelium, the vegetative part of fungus, colonizes plant roots and extends out in the soil to bring in water and nutrients for the plant in exchange for sugars made by photosynthesis. Adding biochar to the soil provides a storehouse for water and nutrients that can be used by plants, and more importantly by the tiny life forms hidden from view.
Too much carbon dioxide in the atmosphere is causing climate change. Simply reducing the amount of greenhouse gases produced will at best only slow the damage. There is a tremendous amount of biomass produced and wasted, much of it taken to the landfill. It breaks down relatively quickly and the carbon returns to the atmosphere as carbon dioxide and methane (which is a far worse greenhouse gas). Even if the biomass is treated as a resource, composted and returned to the soil, the carbon would still soon return to the atmosphere. Making biochar involves burning off some of the material. Not more than the natural breakdown, just faster. But a significant amount of the carbon turns into a stable form that remains in the soil over time. The half-life of compost is a few years up north, maybe one season in the sub-tropics. The half-life of biochar is hundreds of years. The result is that biochar is carbon negative–it removes carbon from the cycle and puts it to good use. Adding biochar along with compost and mulch creates a winning combination.