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Is it easier to make compost in the hot tropics?  RSS feed

 
Conor O'Higgins
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Location: Port-au-Prince
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Hi guys,

I watched a geoff lawton lectures where he talks about the Berkeley method of making compost, where you have to be quite precise. At the end he says something like, "In the hot tropics, that's almost a waste of time because everything breaks down so easily." I've heard similar things from other sources.

So how is composting different in the hot tropics?

In a garden in Haiti, we have raked up a big bunch of weeds. We put this under a tarp and added some water. It is hot enough, big enough, and wet enough to make compost. The only potential problem I see is that there's not enough nitrogen. In a colder climate, I would add manure, but can I ignore that here?

Thanks
 
Dale Hodgins
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Temperature is always a factor. In your heat, things should compost quickly but you still must have a decent carbon/nitrogen ratio. Don't get things so wet that it goes anaerobic. Compost breaks down quickly in the tropics. In the rain forest, most organic material is living tissue and the soil is largely mineral. The job is never done.
 
John Elliott
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Another thing to keep in mind is that in the tropics, insect activity is going on all year long. There are all sorts of detritus eaters munching down on the biomass in addition to the bacteria. What they excrete makes an excellent balanced fertilizer that is too diffuse to burn you plants.

My only suggestion would be to chop your weeds up small so that you can use them as mulch and let the mulch self-compost. Observe how quickly the mulch breaks down, so that you can add more and keep the nutrients flowing to your plants.
 
Su Ba
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Conor, if your weeds are green, then you've got nitrogen. The more lush and young the weeds, the higher the nitrogen. I figured this out by observing my own garden efforts.

Here in the tropics, organic material decomposes year around. Moisture seems to be the deciding factor most of the time. Too wet or too dry, and decomposition slows down. Both compost piles and surface mulch rapidly decompose providing nutrients to the soil micro organisms and thus the vegetables. Since I add mulch regularly and till in the old mulch and fresh compost between crops, I do not need to purchase commercial fertilizer.

I find that I can grow great potatoes and sweet potatoes without manure. I grow them right in boxes that I filled with weeds, grass clippings, plus sprinkled a bit of dirt fortified with micro organisms and burnt bones. It's an old Hawaiian method that really works. By the time the tubers are ready for harvest, the organic debris has broken down into a nice organic "soil".
 
John Alabarr
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I have done numerous attempts at composting in the state of Georgia, USA. I have added all kinds of different things to the piles, horse manure, vegetables, twigs, grass, weeds, etc. What I find is that it decomposes so rapidly down to nothing! There is virtually nothing left in the pile. So instead, what I have started doing is to apply the vegetables, grass, weeds, etc directly to the garden and at the base of my trees in the orchard.

I don't know if ya'all are familiar with Georgia, but it gets hot! There isn't really topsoil on top of the red clay. At most there is a 3/4-1 inch layer of leaf litter and brown grass and there are many bare areas. Decomposition is so rapid that topsoil does not build on top of the clay.
 
Su Ba
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John, I find that organic material decomposes on my farm very rapidly too. As a result I only bother making traditional hot compost piles when I want to "sterilize" the ingredients, such as with manures, seedy material, grass roots that need killing, material that might be housing noxious insects, etc. In these cases I will make hot piles that heat up rapidly and are usually ready to be opened and cooled within 30 days. I don't leave hot piles sitting around decomposing, for as you found out, they continue to rapidly decompose down to the basics. Almost all my hot piles are opened, cooled, and used 30-45 days after starting. If I'm busy or don't need the material, then a pile might go 60 days.

I also use a lot, lot, lot of cold (actually only slightly warm, not hot) compost piles. These are my pallet grow boxes that hold a cubic yard of material. I also have a few keyhole gardens that I use for demonstration that I fill as cold compost piles. Once filled and put into use, the volume gradually reduces due to decomposition. By 6 months of use the grow boxes are around half full....sometimes more, sometimes less depending upon the material used.

Having my compost "disappear" is good as long as I am utilizing the nutrients. I rely upon the compost decomposing because it is my major source of fertilizer. I am constantly replenishing the compost and other organic material, tilling the compost and old mulch into the soil between crops plus adding mulch to growing crops.

Digging material right into the soil and thus bypassing a compost pile is another method I use, as long as the material doesn't need heat treatment. I grow my taro that way. My taro beds are prepared with a trench on either side of the row of young taro. Then over the course of a few weeks, the trenches are filled in with organic material. It is eventually topped with some grass clippings and an inch of dirt or volcanic cinder. As the material decomposes, it feeds the growing taro.

I prefer to lightly till in my compost, as apposed to leaving it decompose on the soil surface. We get tradewinds here that will literally blow away the fine dust and material the compost eventually decomposes down to. I keep my soil usually covered with a light mulch which also helps protect the decomposing compost. With all the effort to get compost into the soil, I hate to see it blow away. And besides, compost as it decomposes is constantly losing nitrogen, so I have read. By lightly tilling it in, I hope that the ammonia ions get used or otherwise bound up in the soil rather than blowing away in the wind.
 
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