Understanding Tropical Soils: Part 3

This article is continued from Understanding Tropical Soils: Part 1 and Part 2.

by Dexter B. Dombro

International Biochar Initiative

With the discovery of Terra Preta, many people want to implement biochar programs. This can be especially difficult on a large scale, but solutions are being developed all over the planet. Some of the examples given here are based on the methodology being developed at the Amazonia Reforestation and CO2 Tropical Trees La Pedregoza and El Encierro plantations in the Orinoco River basin of Vichada, Colombia, together with designs and solutions that have been developed by biochar enthusiasts worldwide. For more information I highly recommend checking out the International Biochar Initiative, of which I am a member.

Tree pruning produces a lot of biomass.

At La Pedregoza we have noticed that when pruning Acacia mangium cultivations, there are approximately 5 KG of branches and twigs being removed per tree. Since there are around 1,200 trees per hectare in an Acacia mangium plantation, this means that there is approximately 6 metric tons of woody biomass available per hectare (2.47 acres). Biomass from pruning at present has no ready markets, so this is a boon to planters, as the pruned material can be gathered and converted into biochar. Many other tree species produce similar results, and as mentioned before charcoal can be made from just about any vegetal matter.

Culled trees have various uses.

As trees mature in cultivations, the ones that are performing poorly are often culled to allow better growing trees to expand and to receive more light. Culling is also a way to better aerate a plantation, especially in wet tropical conditions. This culled woody biomass may have some economic value (fence posts, wood pellets, small boards etc.), but a lot of it can also be converted to biochar. Needless to say, biochar can also be sold to neighbors and others as a processed product. In hardware and garden centers around the world biochar packages for home gardeners can fetch significant prices, which help to support farmers and plantation owners. The point is that tree plantations and agricultural projects generally speaking have sufficient biomass available to implement biochar programs.

Decomposition is slow and releases GHG.

It should be mentioned that if the culled or pruned material is simply left to decompose on the ground, there may be some limited benefit to the soil. However, consider this: it takes many years for a large pruned branch to decompose. All the methane and co2 locked in the decomposing wood is released into the atmosphere, adding to greenhouse gases (GHG). While the biomass slowly converts into organic material, it does not become a retention agent, improving the soil’s CEC. This is why collecting it and converting it to biochar makes more economic and environmental sense.

Traditional charcoal making is inefficient.

Once the benefits of biochar were identified, people quickly realized that traditional methods of making charcoal are not really desirable. Traditional charcoal making involved pits filled with biomass or wood piles being burned and then doused at some point before all biomass is consumed. Unfortunately, this method has two large drawbacks. The first is that all greenhouse gases in the biomass are released into the atmosphere, which is completely undesirable. The second is that on average this method has a very poor 10 to 1 conversion rate, with one ton of biomass producing only 100 kg of charcoal. This makes it economically inefficient and wasteful. Unfortunately, it is the prevalent method of making charcoal in much of the developing world, and in some countries a leading cause of deforestation.

Adam Retort photo courtesy of Chris Adam

The best way of making biochar is to construct retort ovens that rely on pyrolysis or low oxygen burning to convert the biomass to charcoal. Retorts are basically sealed chambers inside ovens that allow the operator to control the pyrolysis burn in a low oxygen environment. The retort is packed with biomass and sealed so that very little oxygen can enter. Some biomass is placed inside the oven area and lit, so that it can start to heat up the retort. As the biomass inside the retort gets hot, it starts to release the greenhouse and volatile gases in the biomass, which are gathered and piped or ducted back down into the oven area, where they burn off while continuing to heat the retort. The biomass inside the retort chamber turns to charcoal. These ovens are environmentally friendly, can be built fairly cheaply using locally available resources and supplies, and have a much better conversion rate of 10 to 3.5, meaning for every 1 ton of biomass one can produce around 350 kg of charcoal.

At La Pedregoza we are in the process of constructing 3 large Adam Retorts, based on a design development by a German Ph.D. by the name of Chris Adam. Our goal is to produce on average 1 metric ton of charcoal per day and to then charge it with organic material so that we will have substantial biochar with which to improve our soils (see the soil sample in Part 1). In Part 4 of this series we will discuss the charging of the biochar and its application to the soil, as well as how best to use wood ashes, which are another by-product from making charcoal.

© 2014 Corporación Ambiental La Pedregoza – All Rights Reserved

 

Understanding the La Pedregoza Forestry Systems

At the Amazonia Reforestation La Pedregoza plantation we are experimenting with a number of innovative forestry systems. People often confuse or misunderstand the terminology used to describe those systems, so this article is meant to provide the reader with a better understanding of what those terms mean. The ultimate goal of eco-friendly tropical tree plantations like La Pedregoza is to either fully or partially implement some of these systems in their day to day operations.

The first term worth defining is silviculture. The word derives from the Latin words for forest and growing, and in its modern context describes managed forestry. The term silviculture includes the controlled planting, growth, composition, maintenance and health of a forest, established for various reasons or needs. Obviously, plantation forestry is therefore silviculture. The planter determines the type of forest to be cultivated, regardless of whether the forest is being deliberately planted or is being regenerated naturally or artificially, for example after logging. The woodlot or plantation owner chooses the type of trees, their density and the planting method to suit their objectives. It should be kept in mind that silviculture is about forestry in its narrowest sense, and is not about more expanded uses.

This brings us to the concept of agroforestry. The word is based on the idea that one can combine forestry with agriculture. Simply put, we are talking about trees on farms. The basic idea is to combine trees and shrubs with crops and with livestock. The planter combines forestry and agricultural technologies for a more varied and productive, profitable and sustainable use of the land. Three types of land use are therefore silviculture, agriculture and agroforestry. Sources like FAO (the UN’s “Food and Agriculture Organization”) and the World Bank estimate that 10% of the world’s small farmers practice some form of agroforestry, while 20% of the world’s population makes use of agroforestry products. The importance of agroforestry is best understood when one realizes that its theoretical basis is agroecology, in other words farming in an ecologically sound manner.

Agroforestry is all about intercropping, having two or more plant species growing in close proximity, and whenever possible interacting and providing benefits to each other. This is especially true for crops that enjoy a bit of shade, which trees can provide. The crops in turn might provide services to the trees, like weed control (water melons for example), or nitrogen fixing (beans for example). From the farmer’s perspective, this multiple use of the land often produces higher yields with lower input costs, and provides significantly more ecological diversity and services than do traditional monocultures. Agroforestry is more biodiverse, as it provides more habitats for birds, insects and other animals.

The benefits of agroforestry include increased wood production, as trees now grow on farmland, with more resources for local socio-economic development, like carpentry wood and wood fuel. Soil fertility is often restored in agroforestry settings, and water quality improves due to reduced nutrient and soil runoff. The trees prevent erosion and help maintain higher water tables, making areas more drought resistant, while providing food security to poor farmers with the additional planting of fruit, nut and oil trees. The planet benefits, because agroforestry reduces deforestation pressure by providing farm-grown firewood and carpentry wood. People practicing agroforestry have also noted a reduced need for the use of insecticides or herbicides. It enhances people’s health, by providing space for the cultivation of medicinal plants. The icing on the cake is the fact that agroforestry also provides long-term carbon sequestration, which helps prevent climate change, which benefits the entire planet.

At La Pedregoza our AmazoniaReforestation and CO2 Tropical Trees programs have added an additional dimension to pure silviculture and agroforestry. It is called Analog Forestry, which is a more biodiverse and environmentally friendly form of agroforestry. This is a practice that is gaining ground in a variety of tropical and sub-tropical locations. In Analog Forestry we employ a system of planned, managed forests whose function includes mimicking local ecologies and climax vegetation. Climax vegetation is best described as the tree and plant life that has established itself over millennia at a given location due to climate and other conditions. Old growth rainforests are examples of climax vegetation. 

This means that the goal of Analog Forestry is to recreate as much native tree and plant life in its cultivations as possible, taking into account the dynamics of natural forest succession. Analog Forests are almost-natural forests, because they try to copy the functional and indigenous aspects of local forests as much as possible. This doesn’t mean that Analog Forests are trying to simply recreate a local ecology. They must also be able to render economic benefits. The key consideration is to first recreate local ecological conditions, before the economic values are considered. This means there is scope to mix native tree species with introduced species, and native plants, fruits and vegetables with desirable introduced ones. Each species in an Analog Forest is evaluated on the basis of its contribution to the functionality and composition of the local ecology one is trying to imitate.

La Pedregoza is a member of the InternationalAnalog Forestry Network (IAFN). The network has members around the planet who are able to contribute ideas, experiences and advice for others within the network. No one starts with an Analog Forest. It is an eco-system that is designed, planned, implemented and managed over a period of time, one that may take decades; much like a natural forest may take decades to mature. The vision is to have a forest that provides ecological, economic, social and environmental benefits that go well beyond silviculture or agroforestry. The use of non-native species, other than food crops, is carefully considered and weighed to address the needs of local biodiversity. This long term vision means that Analog Forests generally sequester carbon for longer periods than do plantation forests. Mixing a large number of species in the design reduces the economic risks that exist in cases where there is reliance on just one or two species. At La Pedregoza our long term commitment and vision is to slowly turn every area into Analog Forest for maximum ecological and biodiversity benefits, while still enjoying financial sustainability.