This Spreadsheet should be helpful in getting a perspective on charcoal additions, to make a "New Terra Preta Soil.

Knowing soil density, the density of "loose charcoal" as it will be applied to the soil, the density of crushed charcoal, the depth to which the charcoal will be tilled in, and a proposed weight addition per square meter, we can then calculate the average depth of charcoal on the surface of the ground after spreading, and the weight percentage of charcoal that will exist, after the charcoal is tilled in to the desired depth.

1: If we know the cost of Charcoal: We can then calculate the cost per square meter for the charcoal, and the increased value of yield and other benefits that would be required for the charcoal addition to have the desired "Simple Payout Period."

2: If we know the value of the increase in yield and other benefits: We can then calculate the maximum permissible cost of the charcoal and its application cost per square meter, and the maximum we can afford to pay to attain our desired "Simple Payout Period."

This approach assumes that the charcoal addition simply allows the soil system to attain a higher potential, EITHER giving a Higher yield with the same level of nutrient additions and attention, OR the SAME yield, with a lower level level of nutrient additions and attention. Only the difference in the value of yield and attention is credited toward paying for the charcoal additions.

Note also that the charcoal additions are felt to provide nutrient retention, soil microbe habitat, and moisture retention advantages to the soil. If the soil was deficient in one or more of these requirements, then charcoal additions could be expected to be beneficial. On the other hand, if the soil was NOT deficient in these properties, then one would NOT expect a financial benefit to justify the cost of the charcoal additions.

Kevin Chisholm