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prevent leaching: cover crop vs forest garden?

 
Bobby Eshleman
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I am in the middle of researching forest gardening and ecology with more depth. I am about done reading volume 1 of Edible Forest Gardens by Dave Jacke and Eric Toensmeier and regarding my question i've read many of Toby Hemenway's articles. I still can't see a definitive answer, so I would love to hear all of your answers!

Does cover cropping and crop rotation prevent leeching as effectively as forest gardening? If your goal is food yield for a family for one or two generations, does the difference matter? What about for truly permanent food production? Is there any circumstance that forest gardening is a viable option when sustainable organic farming is not?

I ask these questions because I see how polyculture agroforestry is needed, because it goes above and beyond sustainability in it's contribution to our planet and health, in a way simple gardening does not. But I still have a hard time convincing others that this matters on a small and urban scale. The fact of less labor put aside.
 
Tyler Ludens
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Personally I think any system of this type needs to include some trees or other very deep-rooted plants to bring minerals up from deep beneath the soil. Simply cycling nutrients on the surface probably isn't sufficient, in my opinion.
 
Marc Troyka
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There's not a simple easy answer to that question. It depends on a lot of things; not all land is best suited to growing trees. Generally trees are best grown on slopes, and field crops in valleys, so it depends on the contour of the land you have and the acreage.

Also, trees require a substantial investment (of work at the very least) in digging giant holes and deep taproot holes, and it's best to have hugelkulture under them and possibly around them to catch water. Depending on what you're working with, it may not be possible to sustain edible trees at all without substantial soil building first.

Personally I like Fukuoka's method of letting whatever weeds sprout grow, and then chop them down with your manure crop, using ecological succession and manure trees for hugelkultur and so on. Fukuoka used only one kind of clover as his cover crop, but I would probably use a variety of grasses, clovers, and alfalfa mixed together. Also keep in mind that once you can get trees established, they provide valuable shade and wind protection that can aid dramatically in water retention; their benefits for soil building are probably overrated compared to the effects on water.
 
Tyler Ludens
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Or you could grow trees from seed....which is not expensive.....
 
Paul Cereghino
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Sometimes cover crops don't establish or are not planted. The occupation of the soil profile by an annual cover crop planted in october is much less than a perennial system.

In the absence of external inputs (or under fierce competition for nutrients and organic matter) the higher production of perennial systems can provide a subsidy to the organic matter consumed by tillage systems.

Perennial systems occupy an early season production niche that is poorly served by annuals... I am harvesting dandelions, good king henry and nettles when my spring transplants have 6 leaves.

In tropical systems the rapid rate of decomposition due to continuous heat and moisture makes any system that is not continuously producing biomass potentially un-sustainable.

Consider the full range of ecosystem services provided by a perennial polyculture--nutrient retention is only part of the issue. In developed sites, groundwater recharge and stream base flow is degraded by the inability of simple and disorganized ecosystems (like annual gardens) to absorb water. somewhere around 5-10% impervious surface can damage stream ecology. Perennial systems, complex soil topography, are necessary to reduce impacts of settled landscapes and recover some of the lost ecological integrity of streams and rivers.

Perennial systems also provide fuel, fiber, medicine, bird and insect habitat, screening, shade, flowers, disease and insect control. and microclimate better then annual systems. Preindustrial people typically put annual systems into perennial cover episodically to allow soils to recover from annual production. The continuous inputs necessary for intensive annual production must come from somewhere... where exactly do your friends get their inputs? Is it sustainable?

I don't think it is an either/or question--intensive annual production systems are in my mind a critical component of the landscape, but don't answer the question posed by Permaculture -- are you being responsible for your means of susbsistance and that of yoru children?
 
Marc Troyka
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Tyler Ludens wrote:Or you could grow trees from seed....which is not expensive.....


Unless you only plan to have it as an ornamental shrub, or unless you have 7 feet of topsoil (which is about 70 years of continuous work) then whether you plant from seed or as a whip or as a mutilated bearing-age tree, you still have to dig a very large and deep hole and amend the soil with all kinds of things. Even if you can get all the materials free or cheap, it's still a lot of hard work.
 
Tyler Ludens
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I tend to not agree with that, as trees grow here in nature from seed without a big hole. They grow on rock ledges with just a tiny bit of soil.

 
Paul Cereghino
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Best landscape practice as recommended by the local ag extension office (WSU) recommends modifying the soil profile, but not the planting hole so that plant adapt to native soil conditions, and points to cases where transplants fail to root outside the amended planting hole.
 
Bobby Eshleman
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Thanks everyone for the input.

Tyler,

Do you know if there are any examples or research to show the deficiency of only cycling annual/shallow crops? Toby Hemenway says that ALL agriculture is destructive. He uses mesopatamia, the dust bowl, etc all as examples, but I am under the impression that these situations did not use cover cropping, rotations, contouring, etc... I personally am not interested in annual farming because it is labor-intensive, but I also want to know what exactly is and isn't a truly sustainable/ permanent system. I don't think it's an either or situation, but it seems that a vast perennial majority would be of major importance in human permanent agriculture because our destruction of natural perennial systems has resulted in an impending threat to our ability to sustain ourselves. So we need to plant forests, but we also need food to sustain human life, the only way to do both is through food forests.

On an urban scale, does a handful of trees matter in the scope of environmental damage?


Troyka,

Would you say that ideally tree growth ought to be a goal anywhere, despite certain conditions requiring significant soil building? Either way i'd be curious to hear why, as well.

Paul,

The benefits of perennial systems are multitude, complex, and IMO are hard to articulate in the face of suspicious monocultural perspectives because perennial systems derive so much meaning from the nuances of ecology and, in my case, ethics.

Do annual rotations inevitably yield a net-loss of nutrients? Does the nature of tropical zone nutrient loss apply to temperate zones?

I have read one source, Dave Jacke's book, that talks about some of the experiments done with forest succession. He explains that when a patch of ecosystem is disturbed (as does annual gardening on a yearly basis), it loses control of ecological processes, including the forces that cause degradation by wind, water, and light/heat, and has been shown to degrade until perennial systems re-establish and start developing the infrastructure to again handle those processes and forces in a productive manner. So correct me if I am mistaking, all annual systems simply don't have the infrastructures to avoid at least some degradation of a site's natural resources. The consequences of this impact, in theory, will effect production within indeterminable amounts of time depending on the situation. Clear-cutting a tropical zone will cause harm faster than a temperate site, for example.

Is this a reasonable way to handle the data and theories?


Unfortunately our mulched bed is not producing as well as previous years when tilled, it is hard to instill faith to family members who haven't done the research and haven't seen other examples. My poor design didn't place any controls on slugs, so our greens have been wiped out, the survivors seem to have stunted growth possibly because our sheet mulched bed hasn't broken down into their preferred soil structure. So far we've only received a few tomatoes and a few strawberries out of everything planted. I personally don't mind a whole lot because the soil is going to be so fine next year. It's just being alone in the vision is not the most fun thing in the world sometimes.
 
Tyler Ludens
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Bobby Eshleman wrote:

Do you know if there are any examples or research to show the deficiency of only cycling annual/shallow crops? Toby Hemenway says that ALL agriculture is destructive. He uses mesopatamia, the dust bowl, etc all as examples, but I am under the impression that these situations did not use cover cropping, rotations, contouring, etc...


I don't know of any specific examples of research showing deficiency of annual cropping with the techniques you mention. The evidence of the unsustainablility of systems without trees is historic, not experimental. Two places to look for research on the sustainability of annual cropping systems are http://growbiointensive.org/ and http://www.rodaleinstitute.org/, both of which have been researching sustainable annual cropping methods for decades.

 
Marc Troyka
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Tyler Ludens wrote:I tend to not agree with that, as trees grow here in nature from seed without a big hole. They grow on rock ledges with just a tiny bit of soil.



Trees in central texas are all short and stubby, and generally the native trees are adapted to the conditions. We're talking about fruit or nut trees, although you could grow mesquite if you don't mind a noxious water-sucking weed. Grow a fruit tree on hardpan (or any normal tree) and it can't grow a sufficient tap root and will grow into a short, weedy thing. Whatever conditions trees are subjected to during their young life determines to a very large extent what the tree will look like 100 years from now, no matter how much soil building you do in the interim; fruit trees generally grow twice as fast as you can build soil.

Paul Cereghino wrote:Best landscape practice as recommended by the local ag extension office (WSU) recommends modifying the soil profile, but not the planting hole so that plant adapt to native soil conditions, and points to cases where transplants fail to root outside the amended planting hole.


That heavily depends on your soil conditions. Here in Georgia, the red clay eats soil as fast as it can be built, and self-compacts every time it gets wet. If you don't heavily amend the hole, trees tend to grow up looking wirey and sick. In more favorable conditions, a better thing to do might be to put down a layer of compost around where you intend to plant the tree, and then seed it heavily with alfalfa and daikon and let it grow undisturbed for a few years. Then sheet mulch over it and build a hugelkulture mound for the seedling to live in. If you have hardpan, anything short of letting daikon and alfalfa grow undisturbed for several years and your tree will not be able to grow a taproot at all. If you have at least 3 feet of soil and no hardpan, you could get away with planting seeds directly in the soil and build soil fast enough to keep up with it. One thing I've seen consistently though, the easier the tree can send down a taproot, the faster, larger, and healthier the tree will grow.


Bobby Eshleman wrote:Troyka,

Would you say that ideally tree growth ought to be a goal anywhere, despite certain conditions requiring significant soil building? Either way i'd be curious to hear why, as well.


Yes, trees provide shade, anchor in contours, improve water retention, and their leaf litter (excluding pines and other acidifying species) aids in soil building. They also produce lots of fun stuff you can only get from a tree . The main consideration, all else equal, is time. Growing healthy, naturally pruned trees takes about 40 years of work and soil building. If you wanted to, say, breed a true-breeding fruit cultivar, the process of selection, cutting down trees, breeding the trees that do what you want, and repeating could take as long as 200 years. If fruit trees weren't all hybridized to death it would only take about 100 years to produce your own cultivar.

Trees can also be used to help succeed an ecosystem, similar to how Fukuoka used them. For remediation, once enough soil has been built you can plant down fast growing leguminous trees which provide shade, wind protection and leaf litter until they are cut down, at which point they can be converted to hugelkultur to improve the microclimate further. Thereafter they will probably regrow to a degree and can help shelter and nurse other less hardy trees.

Another thing, and worthy in its own right, is that building up a deep forest ecosystem can lower the surrounding average temperature by 10deg F or more in the summer. The recent droughts and heat are most likely the result of large scale clearing of forest lands to build McMansions and other such trash that's been ongoing since 2001.


Bobby Eshleman wrote:Do annual rotations inevitably yield a net-loss of nutrients? Does the nature of tropical zone nutrient loss apply to temperate zones?


This wasn't directed at me but after thinking about what you're really asking, I think I have a better answer.

Firstly, tropical conditions don't necessarily imply rapid soil loss. In places like Congo and Zaire, for example, the soil is very deep and very black in spite of the regular flooding that occurs there. The rapid soil loss in Brazil is due mainly to the red and yellow (ferrosilicate/aluminosilicate) clays that eat soil in general. As far as I can tell, the red clay in Georgia and the red clay in Brazil eat carbon to about the same degree, but the extra heat and rain in Brazil makes everything go faster. What's interesting about tropical climates is that you can harvest hay up to 12 times per year, roughly 3-4 times more often than in temperate climates. Technically you could build soil much faster there if done properly.

Second, the purpose of crop rotation is not to prevent erosion and leeching. Crop rotation is only to prevent disease organisms for any one crop from building up in the fields. The basic rule of thumb about soil retention is that if you can see the soil through the crops/ground cover planted on the ground, then the soil is eroding. Basically, crop rotation is a distant second place compared to polyculture and use of perennials, although the reasons for soil loss on chemical farms are multitude. Hay crops can hold soil down very well, and can be used to build it rapidly, but don't provide all the benefits of trees and can't hold large contours as well as trees can.
 
Tyler Ludens
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M Troyka wrote:
Trees in central texas are all short and stubby


Okey dokey.
 
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