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A-gleying we will go!

Editorial: March 2010

Having just constructed a swale at the top of a swathe of vegetable terraces which are rather free draining, I was interested to come across this quote about the use of gley for natural waterproofing of porous surfaces.

What is gley?

Related to the word 'glaze', a gley is like a biological plastic membrane such as is found in bogs, which is formed by a bacterial process that requires anaerobic conditions.

 

Traditionally a technique for sealing ponds and dams, there is potential for the process to be adapted for human-made structures. The Russian-devised version for dams uses a slurry of animal waste (pig manure) applied over the inner base and walls of the dam in multiple, thin layers, which is then itself covered with vegetable organic matter such as grass, leaves, waste paper, cardboard, etc. This is all then given a final layer of soil which is tamped down and the mixture is left for several weeks to allow the (anaerobic) bacteria to complete their task, at which time the dam is ready for flooding.

Gleys have the potential to revolutionise water storage capacity in regions with hightly porous soils. An aquaculture industry in otherwise unsuitable areas scould be one of the benefits of this technique.

Unlike bentonite clay, gley materials are virtually cost-free and are comprised of 'wastes' which would normally be discarded in the normal course of operations. Also, plastic and rubber dam liners may actually be dependent on the same anaerobic process for their own continued effectiveness rather than their lack of holes or punctures ­ ie, it is the anaerobic layer created below them rather than their own membranous qualities which prevent water seepage in the long term".

Because our bit of Welsh moutaiside has thin sandy topsoil, water drains straight through it.  I have established Hugelkultur in some of our newer raised baeds, but the terraced section has remained a too dry problem area for several seasons – hence the swale at the top where nothing wanted to grow. Water harvesting up there was also difficult because all the buildings on site are at the bottom of the slope.  I had wndered about using old leftover clay from my pottery days in the bottom of the new trench, but the Gley idea sounds worth a try.  Watch this space for reports on how it works on the back and bottom of the swale. I’ll let water percolate through the front bank of the swale to irrigate the soft fruit we plan to establish in it, interplanted into fascimes. Hopefully the excess water will then seep down towards the next bed in the series.

I am encouraged in this thinking by a comment I just read about the use of lots of vegetable matter for regulating water in both clay and sandy soils:

“in sandy soils where the water filters too fast and takes nutrients down with it, maybe lots of vegetable matter makes a gley in the soil that reduces speed with which the water goes through the soil and into the sub soil. The speed with which the water enters the earth is something you want to increase in some places and decrease in others, like in sandy soils were it is hard to  hold on to the nutrients in the soil the water  runs through the soil so fast washing nutrients out of it. Organic matter is the answer for both things. is the answer for clay and sandy soils because even if it does not form gley it absorbes and holds more water than sand does. It breaks up clay soils”.

For sealing a pond, the following advice looks worth a try:

"Gley" can be made in the pond in this way:

* Clear the pond bottom of debris, rocks, and all other materials.

* Cover the pond bottom and sides completely with animal manure.

Apply the manure in an even layer.

* Cover the animal manure layer with banana leaves, cut grasses, or

any vegetable matter. Make sure that all of the manure is covered.

* Put a layer of soil on top of the vegetable layer.

* Tamp the layers down very well.

* Wait 2 to 3 weeks before filling the pond.

Yet another way:

“Gley is produced by spreading a six to nine inch layer of very fresh, green manure over the area to be sealed. The manure is then covered with plastic, cardboard, or anything else that prevents oxygen from reaching the manure so that it will ferment anaerobically. The fermentation produces a bacterial slime in one to two weeks that can permanently seal soils. After two weeks the plastic or other covering can be removed and the pond can be filled with water.

Using livestock

Livestock such as hogs or cattle penned into a pond will seal the soil in a way similar to the gley method. Livestock provide the added benefit of hoof action to help mix and pack manure into the pond bottom. The livestock are left in the pond until the bottom has been completely covered with manure and well trampled. Occasionally watering the pond bottom will speed this process”.

Input from readers who have tried any of these methods would be very welcome.


Roz Brown

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