Homemade Terra Preta

Terra Preta is a rich and fertile manmade soil that has its origins in pre-Colombian South American history. It is interesting in terms of both historical significance and modern utility. Terra preta was instrumental in the success of agrarian human civilization in the river basin of the Amazon. More than a dead historical farming technique, it may pave the way for a new method of sustainable healthy agriculture for the future.

Terra preta soil is a thick, rich black soil with high carbon content. Found in the basin of the Amazon, it typically contains a mixture of manure, charcoal and bone. There are two agricultural history schools of thought on terra preta, one theorizing that it was the accidental byproduct of the disposal of manure and waste from cooking such as offal and ashes in locations near human dwellings. This is supported by the frequent presence of clay pot shards in terra preta, consistent with the theorized use as a pre-Colombian refuse dump. The opposing view hypothesizes that terra preta occurred as a deliberate attempt by human beings to fertilize the poor soil of the Amazon area.

Terra preta often contains fragments of archaeological significance and thus it is illegal to mine for it. While it can be found in some areas of South America, such as Brazil, incorporated into potting soil mix, it will not be labeled as such to avoid legal entanglement. Thus, it is not possible for gardeners in other portions of the world to acquire this valuable soil. Unfortunately, the exact process required for creation of terra preta is lost to history, but efforts are under way to rediscover it through scientific analysis of the composition of terra preta soil.

It is possible to make an approximation of terra preta at home. Studies have proved that the incorporation of charcoal into soil improves fertility, even though the predominant ingredient, carbon, is not biologically active. Scientists believe this is because the carbon improves the soil’s retention of moisture, vitamins, minerals and nitrogen. The recommended ratio of charcoal to soil is 30 percent. If immediate productivity is your goal, the charcoal can be mixed with the fertilizer of your choice. However, if you wish to replicate more accurately the original terra preta, natural fertilizers such as manure should be used. You also may incorporate ingredients that would be appropriate to add to compost, such as bones and fruit and vegetable waste.

There are different methods to apply homemade terra preta to a garden, and there is no consensus as to which is preferable. One method involves digging trenches spaced throughout a field and filling those trenches with the terra preta mixture. Another strategy is to spread the terra preta like compost over the surface of the garden. Finally, the terra preta can be spread over the field and then subsequently tilled in to be incorporated throughout. Homemade terra preta requires little maintenance, as there is little carbon loss in this form. Therefore, it should not be necessary to reapply the homemade terra preta more than once every few years.