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Bunbunan Situmorang

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since May 04, 2020
Sumatra, Indonesia 1800m elevation
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Recent posts by Bunbunan Situmorang

Turns out some members of my clan took pity on my and offered up their unused plot for me to work with (this is all communal clan land, but plots have been allocated for private use orally). The watertable there is much more manageable, and earthworks aren't a priority anymore. But thanks to this thread I think I'll be burying woody debris under the beds, which I hadn't previously considered for tree planting, so your advice hasn't been wasted. I'll post follow-up questions in the hugelkultur forum.
1 year ago
Thanks for the replies! I don't need swales for dry season water harvesting, and swales are not my first choice solution. I would prefer as little digging as possible, both to save money/time/labor and to reduce the chances of negative effects from major alterations in the land. I just saw that video by Geoff Lawton, and what he claims swales can do in waterlogged clays (abundant surface water combined with well-draining berms) sounds very attractive. I was wondering if anyone here had achieved those results in practice (and if yes, tips on how to replicate their results).

To recap my thought process:
1. The water table is very high, and I don't want to dig deep open trenches for subsurface drainage (the usual solution in Indonesia).
2. Therefore trees will have to be planted above grade, whether on mounds or ridges.
3. The soil for those mounds or ridges will have to come from somewhere. Most efficient would be a ditch right next to them.
4. Some form of runoff control and redirection towards retention/detention ponds is also necessary. If you are digging ditches to build ridges anyway, might as well use the ditches for this purpose.
5. Your end result is a ditch directing runoff flow together with a raised berm for tree planting. Whether this follows contour, a keyline pattern, or a slight downward slope, in a loose sense I think you can call it a "swale".

Particularly, just as mulch. I often lay down a thick layer of wood and branches and just plant into it.

Yes, in syntropic agroforestry a concave raised bed with a thick layer of woody mulch is also the usual practice. But I'm worried in my situation it won't be enough to keep roots above the water table.

So if your swales are, say 25 meters apart, have the sill drain diagonally into the opposite end of the next swale.

I want to plant coffee in much more closely spaced rows, probably every 3 or 4 meters. If swales are placed this far apart, would you plant interswale rows on grade, or build mounds/ridges but without an accompanying ditch?

I would spread the berm out for the entire width of land between the two swales

Basically make terraces? This would require a lot of soil, and deep/wide swales.

Eucalyptus gets a bad rap because people will destroy the land by growing it in mono-culture, but in a forest ecology with abundant water, they are really an amazing resource for both mulch and building material.  

Yes, eucalyptus and banana are the key biomass trees in syntropic systems, and I plan to use them extensively

Here we have large enough rain events (24" in a day back in 1964, 10" day in 2016) and so much deforested and hardscaped land that I would not do true swales (on contour). I just make the water meander around hugel beds that are almost entirely above the water table, with ponds catching that diverted water on its way. I will also fill any relatively straight standard (desertifying) drainage trenches with woody debris to make the water travel further in contact with biomass.

This sounds like a good possible solution with minimalist intervention. Especially like the idea of filling up the existing drainage trenches with woody debris: at the moment they're an erosion disaster, but modifying them would take a lot of work.

1 year ago
Usually the reasoning is that hugelbeds have a tendency to shift and sink as they decompose, and that trees need to root in solid ground for stability. All the hugels I've worked with have been exclusively for annuals and shrubs, so I haven't seen large trees succeed or fail. Searching permies for "planting trees in hugelkultur" gives mixed opinions.

This article stresses that you shouldn't bury the woody debris inside the berm, but I don't think that's what you were suggesting. Rather, build a regular swale with berm, and then a low hugel on top of that for extra drainage, correct?

People in this area doing conventional modern Indonesian-style farming are inadvertently building huge hugel-swales (although usually perpendicular to contour): after the forest is cleared they push all the wood debris to the sides of the fields, next to the drainage ditches. Biomass growth and decomposition is so fast that these piles of wood start becoming solid mounds within a year. These pictures of the same wood debris (from different sides) were taken only 14 months apart:

Unfortunately as you can see they're only used as wind breaks, except for a few tree tomatoes. I've definitely seen larger trees spontaneously grow on these mounds, although farmers cut them down when they start shading the field too much.
1 year ago
I want to start a syntropic agroforestry system, so I'd be planting trees that grow very tall on the same berms as the coffee. I was under the impression that hügels are not a good place to plant large trees, have you had success with them?
1 year ago
My site is located in the humid tropical highlands on severely degraded land, the original rainforest having been clear cut by a wood pulp company about 10 years ago. The soil that remains is poorly draining clay. We get over 3000mm annual rainfall, with many intense rain events during the monsoon. Large parts of the land are waterlogged for long periods of the year, except the three month dry period (June-August).

Normal practice around here is to dig lots of drainage ditches straight downhill, with vertical sidewalls. Obviously I want to avoid those kinds of ditches, but I also want to plant coffee and fruit trees that can’t tolerate waterlogged roots. Some kind of earthworks will be necessary. Initially I was thinking of planting on mounds, but what Geoff Lawton says about swales for poor draining soils in this video makes a lot of sense. I always though of swales as dryland water harvesting tools, but in this case they would function more as long, narrow drainage ponds and sources of building material for raised ridges.

The site is gently sloped (avg. about 5%), stable clay, and no downhill neighbors, so it should be a safe spot for swales. But while there’s tons of info available on building swales for water collection and infiltration, there’s very little on using them for drainage and keeping roots dry. I’m hoping some people on here might have experience with swales for this purpose and can answer some of my questions.

If I install swales, I’m sure they will fill with standing water for most of the year, if not permanently. Will the berms not get waterlogged? Do I need to compact the swale-facing side of the berm to keep it dry? What effect should I expect in the interswale alleys in this pseudo-chinampa setup?

Normally I would plant agroforestry coffee in lines every 3 meters (with medium trees every 6m and emergent trees every 12m), but that's closer than I’ve ever seen swales spaced. On the other hand, advice about not placing swales too close together is usually focused on maximizing efficiency of rainwater collection, which is not an issue for me. Can you have a denser pattern of smaller swales for this kind of application ?

My site is crossed by several drainage ditches dug by the pulp company when they cleared the land directly above me. If I install swales, would you use them as overflow spillways (perhaps with some erosion control modifications like sloping edges, adding some sediment traps, etc.), or fill them in and start from scratch?

There's lots more to say and ask, but it's getting long for a first post, so I'll leave it here for now. Thanks in advance for any advice.

Some pictures to help form an impression of the site:

Gentle 5% slope down to a wetlands and river, no downhill neighbors. You can also see the thin topsoil and soil horizons in the drainage ditch next to the logging road (my only site access).

Looking directly downslope.

Looking upslope, with old growth rainforest directly next to the site. See if you can spot two people on the logging road for scale of the trees. My site goes to the tree line in the back.

The neighboring rainforest has no waterlogging issues, just beautiful humid leaf mulch. My site was like this less than 10 years ago, making me optimistic that it's not crazy to start an agroforestry system in the current waterlogged conditions.

30cm hole naturally fills with standing water. I expect swales would be filled with water semi-permanently.

Typical example of the drainage ditches that cross my site (although this one is located on a neighboring plot).

The new eucalyptus plantation on clear cut forest directly uphill from me, with a drainage ditch that ends up on my land. If I get an excavator to do earthworks, it will be operated by people who only have experience doing this kind of job, so it would be a challenge to get them to dig the kind of swales I have in mind.
1 year ago