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Question: Do Earthworks such as Swales Prevent Erosion at the Cost of Increased Leaching?

 
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In "The Albrecht Papers," Albrecht says that the most fertile soils in North America are found in the middle of the country where the buffalo used to roam, generally on the great plains, along the edge of the eastern woods. According to Albrecht, the soils become more poor if you travel east or west away from that zone of good soils. Travelling east towards the Atlantic ocean, the high annual rainfall leaches nutrients out of the soil. Forests dominate because rainfall is adequate to support them, and forests are largely composed of carbon, ie. carbohydrates, which can be produced with adequate sunlight and water despite low soil fertility. Travelling west from the zone of good soils, the rainfall is not adequate to support the weathering and biological activity necessary to produce a fertile soil. So the zone of good soils represents the "sweet spot" where rainfall is adequate to produce fertile soil but not in enough excess to leach the soils of their fertility.

In permaculture the ecology of forests is highly revered and many efforts are made to imitate it, so it is interesting to hear Albrecht paint forests in a somewhat negative light.

At any rate, in building swales and other earthworks in rainy climates, when we capture water and allow it to infiltrate and percolate through the ground we are reducing surface erosion and creating a water storage for plants to draw from in future, with many well-known positive effects, but are we also increasing the rate at which minerals are leached from the soil? If so, does that cause any problems on a human timescale, and does it make sense to do something to try to address the problem?

I would guess that the Krameterhof, being on the side of a rocky mountain, has plenty of parent materials which are constantly weathering and replenishing any fertility lost to leaching. I'm in the rolling hills of central Virginia, where I find a lot of quartz but not much else, and I suspect the valuable parent materials are mostly already weathered away. What does Sepp think about bringing in materials such as dolomitic limestone where the mineral content of the soil and is low and mineral-rich parent materials are not abundant? Also, in rainy climates, is there ever a situation (aside from waterlogged soil) where you would try to hurry water off of your property instead of trying to sink it into the ground?

Thanks!
Gordy
 
pollinator
Posts: 2409
Location: Massachusetts, Zone:6/7, AHS:4, Rainfall:48in even Soil:SandyLoam pH6 Flat
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the extra humus/mulch in the swale will lockup and hold on to the mineral.
If you wanted you could use bio-char to prevent even more leaching that is what they use in tropical rain forest if it is good there it should be good for Virginia.

Even in a worst case scenario, if leaching takes away 10lbs of mineral, erosion removes over a ton of soil, plus the minerals in the leave/mulch litter, plus its own leaching, so its still a win to do earthworks. Also with less water the plants need more minerals to replace dehydrated/dead tissue and to make more roots to look for water.
 
steward
Posts: 4618
Location: Zones 2-4 Wyoming and 4-5 Colorado
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I have not read the papers, but I am wondering if the author knows why the plains were so fertile and why they are no longer. Reading the historical records, for instance what Lewis and Clark wrote, suggests a savanna with 8 ft tall grasses and large forests. Our european ancestors have been destroying this land and its mineral richness ever since, culminating in the dust bowl of the 30's ,which will be repeated in time.

My point is that his research may be based on what we have now rather than what they were?

So I believe that the techniques used in permaculture would only help to rebuild what has been lost.
 
steward
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Location: Currently in Lake Stevens, WA. Home in Spokane
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To get a better picture of what happened to the fertility in the Great Plains, check out this 1936 documentary:


Plow That Broke The Plains

Compound that with 50-60 years of dumping chemical amendments which kills the soil microbes.

 
Posts: 135
Location: Sunset Zone 27, Florida
forest garden trees rabbit
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i think people like forests because they are so stable, ie permanent.
i can't think of anywhere in the east US that gets so much rain it is a real problem. there are some parts with clay soil that are prone to flooding, but that could be remedied with easily with swales and ditches and ponds.
here in florida we have very distinct dry and wet season. in the dry season (early spring) there is very little rain at all, so sandy soils without amendments have trouble growing any annual food crops. in the rainy season (fall) it can rain so much that all your mulch and compost can wash away, especially if a lot of tropical storms hit your area. i'm not complaining, i just think it makes life more interesting and definitely points to florida's need for perennial ag instead of annual ag. also most of florida's sand should be earthworked to create raised and sunken gardens to catch any organic matter runoff. i have to say, the gulf has been looking nicer since the ban on phosphates.
is there ever a time i would want to hurry water off the sandy land? yes, but only if it's windy.
this is just my opinion, please don't quote or flame me. people on this board like to take things out of context. you know who you are.
 
chrissy bauman
Posts: 135
Location: Sunset Zone 27, Florida
forest garden trees rabbit
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the middle of the country is relatively flat, so the water is slow moving. isn't iowa a river delta?
you make a good point leaching does destroy fertility in the southeast, no doubt of it.
 
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Great question! I appreciate it!
 
If you try to please everybody, your progress is limited by the noisiest fool. And this tiny ad:
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