Improving Soils in the Humid Tropics of Costa Rica

By Anthony, Apprentice 2020

Syntropic farming workshop at Rancho Mastatal — *Syntropic farming* *workshop at Rancho Mastatal*

In permaculture and agroforestry circles it’s common to hear the idea that we’re not growing plants so much as we’re cultivating rich, healthy soils in which plants will do their own growing. Yet, to this end changing the make-up of soils seems like a daunting job. So how can we go about the task of improving our soils in a simple and efficient way that corresponds with permaculture principles?

The challenge of Tropical Soils

Soils in humid Tropical America are generally found to be eroded and leached. In this region’s ecosystems, about 85% of nutrients are held in plants and animals, so the soils themselves are infertile. Only terraces, floodplains, and new volcanoes keep some soil fertility replenished if land is cultivated (Mollison, 2004). This yields soils that are high in clay content, poor in nutrient content, and often quite acidic. As we say here at the Rancho Mastatal, a permaculture farm in Costa Rica, it’s soil that’s great for natural building, yet not ideal for growing an abundance of food.

The goal with soils like ours is to improve soil texture, increase mineral and nutrient content, reduce soil acidity, enrich microbial life, and increase the quantity of organic matter held in the soil.

Planting a fruit tree during our annual Agroforestry Skills Workshop — *Planting a fruit tree during our annual* *Agroforestry Skills Workshop*

Permaculture & Agroforestry based strategies

In a recent agroforestry workshop held at the Rancho Mastatal here in Costa Rica, a class that worked through concepts of a multi-strata, diverse style of permaculture, the holy trinity of soil amendments for the humid tropics was revealed. The three pillars of improving cultivated soils are

Biomass
The strategy of biomass organized on contour (lines running perpendicular to the direction of the cultivated slope) is the most visible method used here at Rancho Mastatal to improve the soil’s structure and nutritional/mineral content, our ‘organic’ way of applying fertilizer. In the humid tropics, biomass tends to be available in great quantity, and can be used to build up the mentioned contours. Over time these will build to form terraces that greatly reduce soil loss related to erosion and leaching.
Mountain Microorganisms
Mountain microorganisms is a world of its own. Through the fermentation of leaf litter from nearby forests, we cultivate microorganisms which are then applied to our soils, the foliage of our plants, and our compost. We are reproducing healthy bacteria and yeast that, when used in our permaculture systems, will in turn help our plants absorb more nutritional benefit from our soils. To read in more depth about how to make Mountain Microorganisms read this article.
Biochar
Biochar will then provide a long-lasting refuge for these beneficial microorganisms. This is due to its incredibly high surface area within its structure. This special form of charcoal is extremely slow to break down and both directly provides nutrients and minerals to our soils as well as creating a positive feedback loop of topsoil production.

Many ways to develop tropical soils

There are other solid permaculture concepts for improving soils in the humid tropics that should be mentioned here. To deal with highly acidic soils, adding lime at regular temporal intervals is a useful strategy. We tend to avoid planting annuals while opting for perennials, by which we disturb the soil less and reduce potential erosion. Read our article about which perennial greens do well in the tropics here. Over time these plants will help build humus and topsoil. There are plenty of pro tips from the world of permaculture that you’ll find helpful, like adding shredded cane and bamboo species as a mulch for silica and calcium enrichment. This will in turn help to raise pH levels (lower acidity) of soils and reduce leaching and erosion. We add Humanure and effluent from our Biodigestors, this helps build our soil and use commonly wasted products to grow food!