While Guatemala is full of methods of adding plant matter to farm fields, it seems like Mexicans spend more energy on harvesting sediment out of water.  In the Tehuacan Valley of southwest Mexico, elaborate systems of canals and dams are used to apply just the right amount of top quality silt to fields. 

Neighboring farmers all work together to build the infrastructure required to channel water from rivers to nearby farms.  Each farmer builds retaining walls around his fields out of soil, then decides when to open gates and allow flood water to flow from the canals into his fields.  Silt settles out as the water sinks into the ground and the result is about half an inch of high fertility topsoil per flood.

Farmers have about a dozen floods a year to choose from, and most opt to open their flood gates for just three or four.  Since storms in the region are often spotty, silt quality varies widely from flood to flood.  Floods fueled by storms in a certain part of the watershed will wash high quality topsoil into the river while storms in another region result in lower quality silt.  Experienced farmers are able to tell the difference and pick the right floods to feed their fields.  Even when floods contain high quality silt, farmers usually let the first flush of water flow past unharvested since it tends to contain trash and dead animals they don't want on their fields.

We actually saw a system like this at work in the Rio Grande Botanic Garden several years ago (although the primary purpose there was irrigation), and I've been intrigued ever since.  Our creek floods several times a year, but we just let the muddy water flow past, untapped.  Our current garden is up out of the floodplain and wouldn't be eligible for silt harvesting, but this is certainly an idea I'd like to keep on the back burner.

This post is part of our Central American Permaculture lunchtime series.  Read all of the entries: Permaculture implications of traditional Central American farming Leaves as a soil amendment Elderberry makes a good mulch Mexican silting fields Muck makes good seed beds Central American forest gardens Central American raised beds Tablones Cepas Subirrigation

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About us: Anna Hess and Mark Hamilton spent over a decade living self-sufficiently in the mountains of Virginia before moving north to start over from scratch in the foothills of Ohio. They've experimented with permaculture, no-till gardening, trailersteading, home-based microbusinesses and much more, writing about their adventures in both blogs and books.



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