I’m building an agroforest. An orchard of tropical fruit and nut trees, shrubs, herbs, tubers and vines. And this is how it is happening.
This article continues the examination of the tropical orchard establishment patterns and techniques practiced at Rancho Mastatal Sustainability Education Center in Costa Rica. Part 1, found here, examined the goals of our site, the alley cropping layout pattern, and how we manage water. Part 2, below, details our approach to soil, and Part 3 explores our species selection and other agroforestry establishment concepts.
Tropical Soil Ecology
The context of soil and how to manage it starts with understanding our forest ecology and tropical climate. Two major variables, one climatic and the other geological, create quite a different soil conversation in the tropics, as compared to temperate climates (where most soil research occurs).
First, on a geological scale, the lack of glaciation in the tropics during the last ice age never allowed a “reset” of the soil. It never exposed fresh bedrock to the elements as has occurred in the great temperate bread baskets of the globe. This bedrock of course is what slowly, physically weathers into beautiful dark soil over time. The result, to generalize, is that tropical soils are bereft of nutrients, highly weathered, very acidic, rest many meters above underlying bedrock, and are commonly clay.
Second, the climatic variable is that freezing temperatures do not occur in the tropics due to our proximity to the sun (exceptions can be made for altitude). Without “winter” the following occurs:
• There is no build up of organic matter. Nutrient cycling never slows, hummus does not form easily, and there is not, commonly, a creation of deep top soil. (Exceptions to this are volcanic soils, terra preta soils, and tropical aquacultures such as chinampas and rice paddie terraces.)
• Nutrients are storied in plant and microbial biomass, instead of the soil. Through the decay/growth balance they are constantly cycled through this system before they ever have a chance to form a hummus layer.
Soil Fertility Goals
These ecological functions, and the ecosystem structures which underlie them, are our primary templates to mimic. Knowing this, and knowing we are working with quintessential degraded tropical soils, it should be apparent that we are not trying to “build soil”; rather, we are cycling nutrients and increasing biomass as part of a self-regenerating system.
Our soil fertility goals are to:
• Encourage rapid and efficient nutrient cycling.
• Grow living biomass (plant and microbial) to store nutrients.
• Plug nutrient leaks, primarily occurring through leaching and erosion.
In order to accomplish these, we employ the following strategies:
• Pollarded Nitrogen Fixing Trees (NFTs).
• Microorganism cultivation through anerobic bioferments and mountain mircoorganims (MM).
• Biochar Production.
• Bananas planted for microclimate enhancement and mulch.
All these strategies are leverage points that build a fertility “whole” greater than the sum of its parts. These parts and whole include all of our orchard establishment and management techniques, including the successful management of the water entering our property, as discussed in Part 1. How we manage water and soil is intimately interconnected, and you will find as we go deeper into specific strategies that their many functions affect both elements equally.
Nitrogen Fixing Trees (NFTs)
The Nitrogen Fixing Trees that we use all reside in the Leguminosae family. Leguminous plants such as these are abundant and prodigious pioneer species in our forests. The structure and function of this pioneer ecology is an important pattern to mimic. Through a wonderful relationship with the Rhizobia genus of bacteria, leguminous trees exchange sugars in the form of root exudate for soluble nitrogen. The bacteria are able to turn atmospheric nitrogen, N2, into a plant soluble nitrogen, N3. This process is somewhat unique in the plant world due to this mechanism, as they can create their own fertility and thrive on harsh sites. This makes them vastly useful in the tropical orchard.
These trees are planted between 25 cm and 1 m apart on contour, just below our swales. Throughout the year they are pollarded (coppiced or pruned above animal grazing height) to roughly 1.5 m. Spacing and frequency of pollarding is dependent on species. We pollard at this height for visibility amongst the quick growing ground cover and to provide extra shade, which keeps the soil temperature to a reasonable level.
The nitrogen rich prunings are taken to the nearest crop species and used as mulch. In addition to this, as the plants lose foliage from pollarding, they attempt to compensate by shedding their roots, striving for balance. These roots are laden in nitrogen rich nodules which may become available to nearby crop species as decomposition occurs. This is one of the few ways we can insert biomass into lower soil horizons with minimal soil-food-web disturbance. It is important to note that the mechanism by which these nutrients move through the soil is complex and barely studied. It is impossible to know at this point if this has a major effect on nearby plant growth; therefore I emphasize may.
We plant approximately 10 NFTs for every crop tree, which results in an abundance of mulch. The mulch is applied in a donut around the base of the tree. We leave 40 cm of non-mulched space around the trunk of all trees. Biomass pushed up against the trunk of the trees can easily cause trunk rot in our climate. It is essential to provide this space, especially during the rainy season.
The sheer amount of biomass generated from these NFTs mimics the succession patterns of the forest. After a disturbance in the nearby forests, the species which emerge are those most capable of reducing erosion, physically covering the soil, reducing soil surface temperatures and cycling the nutrients made available through the decomposition of the now dead plant material. This minimizes any nutrient leaks. Our design works with these same functions, and in addition cycles nutrients closer to crop species due to our careful placement of pruned biomass. Again accelerating the succession towards a productive orchard.
We work with five principle species and trial new legumes yearly. After two years in the ground these are pruned back two or three times per year. Our principle species include:
• Flemengia macrophylla
• Gliricida sepium
• Acacia mangium
• Erythrina sp.
• Shizolobium parahybum
Species currently under trial include:
• Calliandra sp.
• Acacia albizia
• Acacia auriculiformis
• Senna siamea
• Cassia javanica
• Inga edulis
If any of these prove to require minimal weeding for establishment, are drought tolerant, and have a strong coppice response, then we will propagate them out by the hundreds or thousands.
The above management system is our primary means for creating a self-generating nutrient cycle. It functions with little outside inputs and provides a steady stream of biomass necessary to protect our soil from the elements. With the right tools, primarily a light-weight chainsaw or high quality pruning saw, the work of pollarding these thousands of trees is manageable with a few hands.
We need the microbial life in our orchards to thrive. These invisible allies play so many roles in the soil -food-web that creating habitat and food for them is almost always the true end of other soil fertility means, such as NFT biomass/mulch. A healthy microbial population improves nutrient availability to plants, reduces nutrient leaching, improves soil tilthe and aeration, controls disease-causing organisms and much more. We attempt to harness these functions both actively and passively.
Our strategies and techniques include:
• Creating an ideal microbial habitat.
• Encouraging a high fungal to bacterial ratio.
• Making and applying bioferments and Mountain Microorganisms (MM),
If we do everything we have discussed toward managing water and soil, then we will be creating appropriate habitat. We want scores of leaf litter, uniform soil moisture, and soil temperatures around 70° F or 21° C. Chris Shanks of Project Bonafide calls this the “Field of Dreams” principle: if you build it they will come. Microbial life is perpetually surrounding us, waiting, ripe to grow, multiply, cycle nutrients, and keep this whole wide world in operation.
In addition to this we are particularly interested in cultivating a high fungal to bacterial soil microbe count. That is, we want more of our microbial life to be in the fungal family than the bacterial. Fungi tend to be more dominant in forest/woody/perennial ecosystems and bacteria in agricultural/herbaceous/annual ecosystems. There ability to decompose complex carbons such as lignins and tannins, as well as produce nitrogen in forms that most woody plant need, are functions we can leverage. While we do not yet do any detailed measurements of our soil biota, I believe by using woody mulch, derived from NFT biomass, we will encourage the same microbial populations that exist and contribute to the forest ecosystem we aim to mimic.
Taking a more active approach we brew and apply beneficial microbes using anaerobic bioferments and Mountain Microorganisms (MM). Derived largely from Korean Natural Farming techniques and now popular throughout rural Latin America, these technologies use easy-to-find containers and locally available inputs to brew powerful soil enhancing foliar sprays and soil drenches.
The bioferment we work with is a mix of fresh cow manure, whey, molasses, ash and water. These ingredients are mixed together and stored in a plastic drum with an airlock. After four days this liquid is removed and diluted 20:1 to be applied as a foliar spray or soil drench. This provides a powerful dose of micro-nutrients in a highly soluble form. The best application time is early in the morning, to the underside of plant leaves, when the stomata are still open.
The MM is a batch of microorganisms cultivated directly from the nearest healthy forest ecosystem. Again we follow the same pattern of mimicking the forest, all the way down to it’s invisible life. To make MM we mix forest leaf litter, rice semolina, and molasses together. This is then stamped down into a 55 gallon barrel and sealed for one month days. A small amount of this mix is then placed in a sack and sealed in a 25 gallon container of water and molasses. In four days this tea can be diluted 20:1 and also applied as a foliar spray.
I believe this is one of the most effective, low cost, and low maintenance systems we work with. Our apprentices apply one backpack sprayer (20 liters) every morning to a different orchard area and in a week are able to cover our entire site. We are very happy with this system and in the future will look to expand this system by adding rock dusts, fish emulsion, soluble calcium, and more into the existing bioferment.
All of the above meet our goals: the increased microbial life hold nutrients in their bodies, which reduces leaching, and their death cycles nutrients back into the system in a more plant soluble form.
We make a small amount of biochar yearly to be used in our nursery potting soil and applied to our garden beds. Biochar has been studied extensively over the past 25 years and has proven to be an effective soil fertility strategy, in particular in the tropics. We use two different biochar systems. The first is a cook stove called an Estufa Finca. This was developed by our friend Art Donnelly of SeaChar.org. The second is a larger retort kiln called a TLUD (Top-Lit Up-Draft) made of two 55 gallon metal drums.
Biochar is a fascinating soil amendment that inspires much disagreement and conversation. For us, we are mostly interested in leveraging the unique physical and chemical properties of biochar to reduce leaching of nutrients, improve soil structure, buffer our pH, and provide host sites for microorganisms. Biochar in general has a negative molecular charge which binds well to nutrients and it’s physical structure provides endless nooks and crannies for a diversity of microbial life to seek shelter from predators.
We primary use fruit tree and bamboo prunings for our biochar feed stock. We avoid nitrogen rich feed stock as this nitrogen volatilizes during the combustion process. After a burn, which can be seen in the following photos, the biochar is crushed and then charged. As the burn process removes most nutrients from the remaining carbon, it is most effective to soak the biochar in a nitrogen rich liquid. Typically we use effluent from our methane biodigestors.
The biochar is then incorporated into our potting mix or worked into resting garden beds. Occasionally we apply this amendment directly to tree planting holes, in which case we apply ½ kilo per tree hole and top dress under the mulch another ½ kilo.
Overall biochar does not make up a huge part of our day-to-day work. I find it challenging to find the time and physical space for all the necessary harvesting, handling, and drying of feedstock. This year we will make 60 to 120 kilos of biochar for our gardens.
Bananas, or to be clearer the entire Musa genus, is special to the tropics. Other than the well-documented coconut, the Musa genus, which includes both bananas and plantains, is certainly the most useful plant in the tropical agroforester’s tool box. It’s multi-functionality is extraordinary.
As a plant that grows rapidly in a number of environments, we are able to put it to the following uses:
• Microclimate creation: With it’s large leaves and quick growth, it throws shade over a two to three meter diameter area within six months. This small amount of shade is just enough to change the microclimate for establishing young crops trees by reducing evaporation and lowering soil surface temperatures.
• Food: Almost always the first producing species in our orchards, the banana is a perfect human attractant. Knowing a delicious bunch is ripening in an otherwise slow growing Zone 3 orchard, pulls me in and invites me to visit trees that don’t require my attention but certainly benefit from tending.
• Mulch and Moisture: If you’ve ever cut down a banana trunk, then you understand how much water is held in the trunk. After harvest, or as needed, these trunks can be cut open and applied around the base of crop trees. The moisture in the trunks acts as a slow drip irrigation throughout our dry season. This is the perfect green mulch, mixed with our woody NFT biomass, to enhance decomposition.
We interplant bananas amongst all of our orchards. They are filler crops to be triangulated into empty orchard space. We try to plant two bananas for every crop tree. If we don’t know what we want to do in an orchard space, then we will simply plant bananas to hold that site until we make a decision. You can not have too many banana plants, as they can nearly constantly be chopped for mulch.
It’s the middle of our dry season now. This is when I know if we’ve done our work well. Have we done enough to keep moisture in the soil? Are the youngest trees shaded adequately? What will need a boost of water and when? This is feedback, when we take notes, adjust our plan for the year ahead, and learn and learn and learn!
For me it comes back to our goals and whether we are moving toward them or away. A quick review of our goals reminds us that all of the above, NFTs, bioferments, MM, biochar, and bananas are all working to create habitat and food for the microorganisms that run the show. Life in the tropics is teaming. Our ability to leverage these techniques, time them appropriately with plant needs, the arrival of the rains, and our own management capacity is what will create a fertility “whole” in an otherwise challenging landscape.
Our next step in establishing our orchard involves choosing appropriate species. In Part 3, we will look across families and explore climate analogues while highlighting different underutilized crop trees that fit our landscape and context. In addition to this we will discuss concepts around stacking in time and space, moving from establishment patterns of management to climax patterns, and the tools of the trade.
Permaculture Design Certification Course
We are hosting our 7th annual Permaculture Design Certification course this April 17th to May 1st 2016. If you are interested in learning more about our site, the methods we use, and our programs, consider joining us! Info can be found on our website at the bottom of this page
About Rancho Mastatal
Rancho Mastatal Sustainability Education Center is an education center, working permaculture farm, lodge and community rooted in environmental sustainability, meaningful, place-based livelihoods, and caring relationships.
We offer profound, innovative and authentic apprenticeships, residential workshops and guest experiences. We practice, promote and teach about natural building, fermentation, permaculture design, renewable energy, agroforestry and more.
Our campus encompasses more than 300-acres of picture-perfect waterfalls, crystal-clear rivers, idyllic swimming holes, impressive trees, extraordinary wilderness views, and pristine habitat for the area’s rich flora and fauna. Visitors and participants have access to over 14 km of trails, an extensive library, our working permaculture farm, and the tireless team who make the Ranch such a unique place to learn.
We are located in the rural farming town of Mastatal, situated on the edge of the last remaining virgin rainforest of Costa Rica’s beautiful Puriscal County. It is a wonderful place to take in Costa Rica culture, practice your Spanish, visit other permaculture projects, or catch a pickup game of fútbol.