[permaculture] Question about acidic soils in the tropics...

Toby Hemenway hemenway at jeffnet.org
Tue Mar 11 14:50:18 EST 2003


Let me ditto Robyn's note on tropical soils, and I've come from a temperate
background and it took me a while to get clued in to tropical growing.

For the reasons Robyn states,

> warm temperatures and high rainfall = constant leaching,

the life and nutrient cycles are not mostly in the soil, as in temperate
climates, they are in the vegetation. So the key is to get things growing
fast and get the cycles happening above ground and in the litter. Fill the
air up with plants. Besides low-growing herbaceous mulches, get mulch shrubs
and trees happening: Intercrop food trees and bananas (a heavy feeder but a
great mulch producer) with Calliandra, Gliricidia, Leucaena, Inga (nice
multifunctional one there), Erythrina, and other N-fixing trees. These will
pump out nitrogen along with tons of soft growth, and most can be just
snapped off by hand (coppicing) and tossed on the ground. Saw down the big
ones for fuel and poles; in a year in wet tropics they will be 2 inches
thick. 

Keep renewing the mulch every few weeks since it will break down fast. But
it will grow fast, too. Augment with fertilizers as Robyn said. And plant
the mulch densely to keep out the grasses and other plants that will move
into it quickly if you don't. Then your job is just to manage the closed
canopy so it doesn't get too dense, cutting back the NFTs to waist height
every few month, and pulling out less-valuable trees as they get big. The
closed canopy will keep things cooler and break the rainfall's intensity.
 
The Polynesian agroforests are beautiful examples of how stable these
systems can be. In Hawai'i we saw ancient agroforest that surely hadn't been
tended for a century or more (kukui nuts, palms, pandanus, mango, with a
taro understory) still lush and productive with a deep mulch layer. Big
carbon-shedding trees like palms and pandanus build up mulch layers in a
hurry.  Until I saw tropical systems, I didn't realize how many of
Mollison's ideas work much better in the tropics than temperate climates.

Toby





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