Fertility in the Humid Tropics
When looking at the wonderfully lush and abundant rainforest that harbors one of the most biodiverse ecosystems on the planet, it is difficult to believe that the soil that supports this ecosystem is, incredibly, quite poor. This is due to various factors that lead to the extremely tight nutrient cycling that occurs in the humid tropics and they are:
1. Because they are the oldest forests in the world and the mineral-rich rocks in the root zone have been completely weathered, most of the nutrients are found in the biomass of the forest.
2. Due to the high rainfall any nutrients not tied up in biomass are quickly leeched out of the soil and consequently leave the system.
3. There is little topsoil and soil carbon stored in the soil because of the high metabolism of the soil microorganisms due to the high temperatures and humidity and the soil carbon is respired into CO2 by the microorganisms.
This means that once the great forests are cut down it is a complicated task to restore them, because the nutrients that supported such diverse and vibrant life very quickly and permanently leave the system through leaching. To make matters worse the abundant fungi and microbial life that were vital to the breakdown and mineralization of the constant addition of fallen biomass on the forest floor, now are starved for a source of carbon and begin to eat the stored organic matter in the soil, eventually even devouring the accumulated humus. This means that the pasture will rapidly end up without minerals and nutrients and also without soil organic matter, which is an important source of fertility for any ecosystem. Then if you add to this situation cattle that compact the soil and destroy the soil structure you end up with quite compacted and infertile soil. This is why once humid tropical forests are cut and planted to grass they quickly degrade (currently millions of hectares) and take a very long time to recover through natural regeneration and succession.
It is important to say that this description is a gross simplification of incredibly complex processes involving interactions between thousands of species of flora and fauna in the rainforest ecosystem. However, it is important to understand the basic ecological processes that drive fertility in this context in order to then talk about possible avenues for ecosystem restoration on a broad scale.
In contrast to the humid tropics, ecosystems in the temperate climates or tropical climates with a drier climate (under 1000-1500mm rain/year) the leaching process is much slower and the soil holds more nutrients because they do not so quickly leave the system when not stored in biomass. In a colder temperate or in a drier climate this would be reversed and the soil holds the majority of the systems nutrients. This is why temperate pastures can be quite fertile and can support diverse and abundant life and change relatively easily to forest cover (providing there is adequate rainfall).
Regenerative Farming in the Humid Tropics
About 3 years ago I, like most people in the world, didn´t have a clue about any of this and the first year we lived here I went out and lovingly planted hundreds of fruit trees into the abandoned pastures. I dug nice big holes and gave them great compost and kept the grasses at bay; I even mulched the trees with cut grass and other materials, just like it says in the Permaculture handbook and all over youtube. And they all died. They had plenty of compost, sunshine, and more than enough rain and I could not figure out what went wrong. This is when I first saw the Life in Syntropy short movie about Ernst Gotsch and Syntropic Agriculture and a light bulb went on. That was when I discovered the concept and the importance of succession.
In case you haven´t seen it:
Since that moment I have tried to read and learn everything I could about forests, succession, and syntropic agriculture. And I have made several attempts at establishing a productive system on our degraded pastures. The first was a small pilot lot where I planted cassava, pidgeon pea, plantains and bananas, many different species of fruit and hardwood trees, and a cover crop. It grew well at first but as soon as I decided to cut the natural regeneration on the paths to mulch the beds, the system collapsed.
This is the system 2.5 years later:
This is mexican sunflower, usually a very rampant bush from the early accumulation system. 2.5 years later it barely has any leaves
Some 2.5 year old cassava obviously having some trouble
This pidgeon pea is truly in a sad state and flowered once in 2.5 years but never produced viable seeds.
Fast forward to November of last year when I decided to buy seeds of unproductive and mostly leguminous plants and trees (Canavalia, crotalaria, pidgeon pea, cow pea, acacia mangium, gmelina, and gliricidia), these were the seeds farthest back in succession I could buy commercially. These are species that are commonly used in ecosystem restoration worldwide. I figured in the pilot lot I tried to establish plants that were too far ahead in succession from the system they were going into so I brought in seeds that were as far back as possible. I cut and limed the 3000m2 lot of degraded pasture and broadcast the seeds, and I had great germination but then the grasses and bracken fern overtook everything I planted.
This is the system 9 months later:
I honestly think my intervention set the system back in succession unfortunately. The plants that had germinated so nicely died off quickly and the bracharia grass dominates still
This is a lone cow pea, 9 months later it hasn´t grown past this point or even flowered. For reference, I am already harvesting cowpea from the coffee system I planted 10 weeks ago
This is a breadfruit tree that I planted about 2 years ago. Instead of growing the poor tree is actually shrinking, despite applications of compost, mulch, and lime.
These experiences brought me to the conclusion that seeds of plants that will grow in the bracharia dominated degraded pasture systems on my farm are not commercially available in Colombia. I also discovered that there were a great variety of plants that had not only have evolved to grow just exactly in these conditions that I have on my farm, and that I didn’t even have to plant them! When I decided that instead of fighting with the bracharia I was going to let it grow together with the early secondary growth and let mother nature do the heavy lifting of moving succession along, everything clicked.
In the humid tropics damage done to the land after years of cattle grazing cannot be fixed with NPK fertilizers, herbicide, pesticide, and fungicide. When we arrived at this farm there was a crop of 1.5 hectares of plantain that was a year old, that the previous owner had planted (with the money from an ag loan) following all of the directions of the local agronomist. The plantains were so diseased that at one point he told us they had to spray a part of the lot with glyphosate to kill off a hundred or so plants that had a fungus (locally known as moco) so they wouldn’t spread the disease to the rest of the crop. The previous farmer got one cutting from the plantains and decided to put the farm up for sale because he couldn’t make any money from this farm. Obviously, these are things that you learn AFTER you buy the farm.
Farmer Managed Natural Regeneration
At our farm, one of my major goals is to find a way to make restoring degraded ecosystems in the humid tropics profitable for the farmer (me). The community where we live is pretty typical of many rural communities in Colombia; there is not a lot of labor available, it is logistically difficult and expensive to bring in inputs from outside the farm, most arable land has been degraded by conventional agriculture past the point of being economically viable, and access to capital is difficult. So any viable solution has to depend heavily upon endogenous resources of the farm (intense sun, abundant rain, natural succession) and need to be easily adopted low-technology techniques.
Example of Farmer Managed Natural Regeneration (FMNR) in the drylands of Niger; photo credit: Mongabay
In our pastures, I have adopted a technique that has become very popular for restoring dryland degraded ecosystems in Africa which is called Farmer Managed Natural Regeneration. Essentially this means taking the natural regeneration (weeds) that grows rampantly with the graminea species; recognizing that these plants are the best adapted and most prolific plants at this point of succession of the system, and managing them with the same techniques you would with any plant in a syntropic agriculture system (pruning and coppicing mature stems). By managing this secondary growth we can move the degraded pasture system forward in succession where the farmer can begin to produce food and other
products much faster than would naturally occur. Eventually the secondary growth will shade out the grasses and at this point we can begin to more heavily intervene and establish productive syntropic agroforest systems. By far this is the most efficient way I have found to work with degraded pastures in the humid tropics.
There are many benefits: 1. This leads to a very diverse early accumulation system that will quickly shade out the bracharia and other gramineas.
2. The natural regeneration are plants that have evolved on this land for thousands of years and are the most prolific and rampant possible, and they cost the farmer nothing.
3. The “weeds” that grow naturally are responding to germination conditions of the soil and are the natural response of the earth to restore fertility to the system and decompact the soil.
4. The high diversity of the natural regeneration feed a high diversity of microbial and fungal life and when the moment comes to plant production and biomass crops the soil will already have recuperated some biological activity.
5. By managing the natural regeneration and cycling the nutrients in their biomass we avoid the senescence phase of the system which can invite fires and keep this early accumulation system locked in a cycle of infertility (very common in our community).
6. The management can be done perfectly with the humble machete.
7. This technique is has very low labor requirements per hectare and is used on land that often is abandoned due to loss of economic viability, which means that the opportunity cost to the farmer is very low.
8. When the gramineas leave the system and it is time to plant accumulation production species there is a large amount of biomass to cover the soil and feed the production species. Also the established plants together with their mulch give enough protection to the next consortium that direct seeding is possible. This saves the farmer labor and investment.
9. This system is extremely resilient in our modern climate variability because it uses all native species.
10. Pruning and coppicing the native species causes them to thicken their trunks and main roots which will assist in breaking up the sub soil as they grow.
Farmer Managed Natural Regeneration is an economically viable and easily scalable solution for farms with unproductive and degraded pastoral systems in the humid tropics. Compared to the establishment of conventional perennial systems the investment is almost nonexistent, and because the production species can be direct seeded due to the mulch and protection the native plants provide, the resulting syntropic or agroforest system will become profitable much faster after production starts as compared to a conventional system. This technique for managing the native secondary growth of pastures follows the same philosophy of Syntropic Agriculture but in some degraded systems it is more efficient to start with the natural regeneration and in the right moment introduce production species rather than expending so much labor and money in establishing biomass species to regenerate the system to the point of production.
The degraded landscapes of the tropics are causing regional climate instability and small and large holder farmers can contribute to the solution by bringing their farms back into profitable production while restoring the incredible native biodiversity, essential hydrological functions of the land and, of course, sequestering a great quantity of carbon in the process. This is the reason that we started our agroecological pilot farm in a place where all of the landscapes are in a state of extreme degredation, we want to find and demonstrate agricultural techniques that are capable of changing the dynamic of poverty and ecological
degredation that has taken over much of the rural tropics. It has not been an easy path finding solutions to the pervasive and complicated challenges tropical farming faces today, but in the eloquent words of the Joel Salatin “we have the incredible privilege of having been a visceral participant in touching creation as a healer” and that makes it all worth it.