[Terrapreta] John Todd Trench Method

[David Yarrow]

Making Terra Preta
by Dr. John Todd

We taught watershed management in Costa Rica, and needed ponds to grow fish, 
but local soils didn't hold water.  Based on terra preta, we mixed clay, 
charcoal, woodash, horse manure, organic matter (banana leaves), carbon 
sources like coconut coir, and molasses.  This mix was extremely 
biologically active.  After inoculation, it seemed to roil with microbial 
activity. As pond liner, this mix held water, but also was a potent source 
of ecological activity.  We made a few small ponds.  What most struck us was 
this mix turned dark, and was fertile to plant life.

Winter 2007 in Costa Rica was dry, windy.  Our associates began a commercial 
farm on worn-out land.  Their experiment combined terra preta formation with 
compost.  Trenches dug a meter and a half deep, filled with tree limbs and 
branches, set on fire. Once combustion is initiated, soil and green organic 
matter is put on top to slow combustion and lower oxygen. This creates 
charcoal.  As the pile cools, clay soil and green matter-especially banana 
stocks-is added to inoculate the compost.

In the future, trenches will be dug on contour slopes of hills, downside 
planted with vetiver grass to control runoff, capture moisture, and powerful 
"sinks" to prevent nutrients from leaching downhill and off the farm.