My chosen internship project at PRI Zaytuna Farm was to stabilize and prevent erosion on a steep slope from an excavation back cut. I also wanted to build topsoil and increase fertility as most of the slope is subsoil clay.
This is a picture of the slope before doing anything to it
I decided to try the Net and Pan method described in the Permaculture Designers’ Manual by Bill Mollison. Net and Pan utilizes the soil-stabilizing and soil-healing power of trees, combined with miniature earthworks that slow the water and move it to the trees, so they can become established quickly.
This picture demonstrates how beneficial trees are in stabilizing slope
Next, as suggested by Geoff Lawton, my friends and I moved a cattle cell onto the area to eat up some of the vegetation. I would have liked them to stay on longer to really make an impact, but by the time I learned from Tom Kendall that that would be the ideal, the cows were being moved. So, they helped give it a nice mow. Before I brought the cows in I harvested the Mugwort (Artemesia vulgaris, a medicinal herb with a whole range of uses) and dried it, along with saving the seeds.
Next I made small flags out of bamboo and with flagging tape
set up where I wanted the trees to go
Then I dug the drainage ditches and tree holes for the net and pan. Note the subsoil clay.
Then I planted the trees with compost around them, to give them a good start in the clay subsoil, and added worm juice to boost soil life. Worm juice is the water that drains through a worm farm; it is full of beneficial micro-organisms as well as nutrients. When I poured the worm juice down the drainage ditch to the tree I noticed it was flowing past the tree and down the next drainage ditch. So I used clay to create a spillway, higher in elevation than the soil level of the tree, but lower in elevation than the sides of the ditch. That way the water pooled around the tree, hydrating it, before flowing down the channel to the next tree ([shown in diagram above). I chose the ice cream bean (Inga edulis) because I have seen firsthand how amazing it is as a pioneer. It can grow quite large very fast and handles heavy pruning and degraded soils very well. It’s also a nitrogen-fixing legume. If the correct micro-organisms are present in the soil they will form nodules on the roots of the legume and take nitrogen from the air and feed it to the plant and surrounding soil. And, whenever the ice cream bean tree drops its bean pods (the insides of which taste like ice cream), or whenever the branches or leaves drop, the organic matter, rich in nitrogen, is broken down by soil organisms and fed into the next stage of succession.
This is a ”Wild” ice cream bean growing in a food forest at the Permaculture Research Institute
The main tree in this photo is an 11 year old ice cream bean
On the top of the slope I planted citrus trees, specifically Bush Lemon that will be grafted later with other citrus. I put them at the top of the slope because it levels out up there and will be harvestable. I was going to put them at the bottom as suggested in the manual, but I learned that citrus trees do not enjoy ‘wet feet’, and the bottom of the slope is quite wet, as you’d expect. Overall I would have planted a lot more diversity had I had access to a greater diversity of ready-to-plant species. I also planted the types I did because for the top of the hill there are plans for a new solar power station so I couldn’t do tall species or plants that could not be coppiced/pruned well.
Next I sheet mulched the trees, first by putting down newspaper and cardboard
(note the white mycelium matrix growing on the newspaper)
Then I put mulch around the trees, on top of the cardboard/newspaper. This is the Bush Lemon
in the photo (with a bamboo stake to show where it is if and when it is overgrown with
cover crops and volunteers).
Next I planted Singapore Daisy (Sphagneticola trilobata). This easy-to-cultivate cover crop will out-compete the grass in time and is excellent at holding soil and preventing erosion in extreme rain events. I also planted Mugwort (Artemisia vulgaris) because it was already growing well on the slope and it is a medicinal plant as well as a mulch accumulator.
This is a picture of my friend spraying a potent biological preparation of Actively Aerated Compost Tea, Bio-Fertilizer (a fermentation of facultative anaerobic micro-organisms and nutrients), and “Pho-si-cal” (a blend of double burnt bone and burnt rice husk — this preparation is full of: phosphorus, silica, and calcium). Paul Taylor calls the blend “Preparation 252”, and this mix was more potent than normal, but definitely not too potent. This spray brought literally billions of beneficial organisms to the soil; hopefully they will proliferate and help speed the healing of this landscape.
This is a picture of lab lab, a cover crop. It is a nitrogen-fixing bean that can be rather rampant. I dug small patches for the seeds as well as casting them randomly where there was disturbed soil. I added compost onto the seed beds as well as casting compost onto the hill.
Then I watered the mulched trees, and cover crop seeds with gravity fed water from a nearby dam (pond/reservoir). I used the opportunity to test the channels and it was great watching the water flow down, around a tree, and then out the downhill channels to the next tree.
Then to finish it off my friend gave me a hand “whipper snipping” the grass, turning it into beneficial mulch for the cover crop — the lab lab that will hopefully overtake the grass.
I did not have enough time to complete the irrigation channels of the net and pan, and when I realized I would not have enough time I focused on just planting all the trees correctly and getting the cover crop in. Part of the slope has net and pan channels and part of the slope does not — but the whole slope has the same species of trees planted in the same way. This should prove an interesting demonstration of how beneficial the channels really are to a forested slope system.
All together the slope now has 36 trees (thirty ice cream bean, and six citrus). It also has a lot more soil life than before, and which should continue to grow. And it has a nitrogen- fixing cover crop that will continue to bring fertility and stability to the site.
Special thanks to Geoff Lawton, Paul Taylor, Steve Gadin, Rachel Euell, and Randall and Valerie Wedin.