Farming in the Tropics

Agriculture is soon to be in a tough spot down here, as it is in many parts of the world where the agriculture is subsistence based. In the last twenty years, the population has exploded, due to the combination of significantly improved transportation and better healthcare opportunities. And the explosion will likely continue into the next twenty years as well. Many of the farmers in their middle 40s have grandchildren the same age, or older, than some of their own children. But while the population density increases at such an alarming rate, the land base remains the same, with a resultant loss of fertility due to over-cropping. Farmers are often walking five miles just to find land fertile enough to grow their rice or dry season corn crops. And at this distance, they are bumping up against the farmers from the neighboring villages.

Slash-and-burn agriculture is a major component of "shifting cultivation," and this implies a shifting (moving) population as well. And, for the past five hundred years anyway, the Maya have been a shifting population, drifting from one location to another as the forest around them fell to their axes and fires. After 7-10 years there will be sufficient regrowth to produce another crop. The key here is that enough organic matter, old enough to break down at different rates, will havegrown up in this period of time. When a farmer chops and burns, the ashes feed the crop. When he chops and doesn't burn, it's the woody brush that breaks down and feeds the crop. So the fallow period can be shorter if the slash is not burned. Burning the slash saves significantly on work. The fire removes all, or most of the slash, providing a weed-free environment to plant into. And the ash provides a more concentrated, quick-release fertilizer. With unlimited land available for planting, this is the obvious choice. But in the short term,it's more damaging to the soil. Many of the farmers realize this, and are not burning anymore, except for rice, which is work enough on a burned field. It would be ridiculously difficult without burning.

The tropical forest also regrows at a rapid rate in contrast to its temperate cousins. The Gmelina tree on the left is only three years old. (That's me in the oval.) Twenty-five years of regrowth on a burned agricultural plot will show little sign of human intervention, other than the occasional bit of charcoal. With the right conditions, there will be 60-80 foot trees and very little underbrush at the end of such a short period of time.

Tropical forests differ from their temperate cousins also in the relationships they have with the soils with which they interact. In the temperate forest, the fertility resides in the soil, being fed each year by the leaf fall and the activities of the resident plant, animal, fungal and bacterial communities. Tropical forests are much more dynamic entities. They not only drop leaves regularly, but they also drop large limbs, as well as entire trees, on a daily basis. After a heavy rain here, say anywhere from 4-10" in a 24-hour period, I will often hear something large falling daily for the following week, and this just in the small radius of my hearing. The organic matter soon breaks down to humus, and the nutrients are taken right back up into the shallow roots of the trees and other plants. (This happens very quickly. A 30" diameter gumbo limbo tree fell on our farm in the hurricane four years ago. At the time of this writing, there is nothing left of it to see.) There is no topsoil to speak of here, save a 1/8" layer of humus. This is precisely why deforestation is so disastrous in tropical forests; as the trees go, so goes the bulk of the fertility.

And so too with agriculture. A system of continual cropping can conceivably be managed, as long as more nutrients (organic or chemical) are returned to the soil than are taken off during the harvest. This is a difficult equation to balance, especially by a population of farmers who spend all of their working lives just feeding themselves and their large families. There are little time, calories or money left over for taking care of the soil. Traditionally, there was no need to do so, as they would simply move on to another place. The problem of soil fertility is a new one for the village farmers to face.

Around here each farmer has around thirty acres to claim as his own. He plants one or two acres of corn once or twice a year. Sometimes beans, and sometimes rice, as well, but corn is what he can't live without. Then he also has his permanent crops, such as cacao, citrus, pineapples, mangoes, coconuts, and coffee. Even though many of these crops are grown together in a mixed grove, they still take up space that will be unavailable for corn.

There are systems in use in Honduras and other Central American countries that use velvet bean (Mucuna pruriens), a vigorous climber, and other leguminous cover crops. When the corn is 6-weeks-old, the cover crop seed is scattered in the field and the weeds are chopped on top of it. This is a tremendous savings of labor over actually planting the beans in the ground with a planting stick. The weeds falling on top of the seeds act as soil might to protect and nourish the seeds. By the time the corn is harvested in approximately six more weeks, the cover crop is growing strongly. In another few weeks, all that can be seen is a mass of vineage. Eight months later, the cover crop is chopped down to the ground and the next corn crop planted into it. This system has been proven to be sustainable for twenty years and more. Some of the farmers here in Columbia are aware of this method, but only a couple farmers that I know of are experimenting with it.

The farmers' resistance can be easily understood. There are two kinds of velvet bean, one of which produces an extremely itchy powder on its dry pods. This one tends to be more common than the other, non-itchy type. And so a farmer, myself included, would want some proof that he's got the non-itchy variety before sowing it in his favorite cornfield. Culture is another factor. This is a fairly new concept, and is therefore slow to take hold. There has always been somewhere to go, within walking distance, where a farmer could find fertile soil.

As I finish writing this article, I am thinking about planting my annual black bean crop in the next month or so. I need time to chop the bush and then let it decay for three or four weeks before re-chopping it and planting the beans. Even in my short time here, I've learned that I can't get two successive bean crops from the same field. I have jack beans (Canavalia ensiformis) on last year's field, and will chop that and plant into it experimentally, but, like all farmers everywhere, I wouldn't consider only doing that. I'll also chop some 7-10 year old bush, and plant my beans into it, knowing it will give me a good crop.

I'm also experimenting with growing my own mycorrhizal soil enhancers to use especially for vegetable growing. The first batch will be ready to use in November, and I'm looking forward to trying it out. Look for my article next year to see how it all worked out.

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