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by Poppy

15th Feb 2023

Back in July 2021, a group of Global Gardens volunteers collected and tested soil samples from a few different areas of the garden. We looked at the samples through the microscope in an online workshop with Compost Mentis - a composting co-operative based in London - and did some creative writing and visioning inspired by what we saw. We met some mysterious creatures found residing in our compost pile - including nematodes, gastrotrichs and ants, and talked about ways of celebrating our garden's compost more in the future.

This winter, as part of our 'Together for Our Planet' climate action programme supported by The National Lottery Community Fund in Wales, we invited Compost Mentis to run a follow up 2-part workshop focussed on humanure and DIY soil testing.

The workshop was an opportunity for members of the garden and other interested folks to learn about the nutrients, biology and chemistry in composted poo, and compare it with other soils and compost from around the site. It was great to welcome Compost Mentis members Hari and Olly to the garden in person after working with them virtually.

In-person Workshop

Hari and Olly began the workshop with an introduction to the idea behind the Compost Mentis co-operative. This was a space for learnings about setting up as a workers’ cooperative, and the relationships between compost, communities and cooperatives. Hari reflected how many of the principles of composting are applied to how Compost Mentis work as a co-operative - including slowness, interdependence, diversity. Hari also highlighted the social justice focus of Compost Mentis and how they are working to composting toilets more accessible to the public, including for those with disabilities.

We then explored some of the different soils of the garden, digging up some soil profiles in the outdoor play area, kitchen garden area and the orchard to build an understanding of how to qualitatively evaluate soil health. We also prepared some soil samples for further chemical analysis (including for soil nutrition and contamination). We learned about "peds" (understood as aggregates of soil mineral particles with or without organic materials) and "clods" (chunks of soil formed artificially by working the soil when it is too wet either with machinery or by hand digging).

Olly explained how worms are a good indicator of soil helath. For a 20cm3 sample, he suggested healthy soil sample should include around 16 worms. He encouraged us to try to identify the different worms in the sample since they can be indicative of the soil quality. In the sample from the outdoor play area, we found around 6 worms - ranging from quite large worms, which help aerate the soil to smaller pinker ones, which tend to be found around the roots of plants. We also collected some soil samples from the compost heap. As we pulled back the carpet which we use as an insulative cover for the heap, many worms, woodlice and a few centipedes were revealed.

We then moved on to our compost toilet, opening it up for the first time since it was installed in 2018. Our disabled-access dual chamber compost toilet is designed and built by Natsol.and funded by the National Lottery Community Fund in Wales. Since it has been used sparely, mainly for pees rather than poos, it has not been necessary to switch the chambers over. However, with Olly and Hari present it felt rude not to look more closely at the chamber in use. We opened up the chambers and discovered some nicely decomposed humanure. We took a small sample for further analysis and testing. We also spent some time discussing the use of the compost toilet. We agreed that we should keep it clear for acess (and prevent it from becoming a storage area!) and that we should plant some comfrey and nettles around the soakaway, where urine is diverted since they are excellent converters of the high levels of nitrogen draining off from human pee.

As we observed the inner workings of the compost toilet, we discussed the benefits and challenges of humanure. It turns out human poop is actually a really good source of nutrition. However, it is recommended that it rests for around 4-6 years before applying it as a mulch. Humanure can be an excellent mulch for fruit trees and shrubs. However, it is generally avoided from vegetable crops since it can potentially be a vector of parasites/e-coli..

We returned to the classrom with some of the soil and compost samples to look more closely and moved on to a local community space where we use electricity to power up Hari's microscope. We saw quite a diversity of micor-organism life. It was interesting to see the energy contained within the seemingly inert samples - with nematodes, and bacteria pulsing. Hari spoke about the energy of the compost heap that in many senses remains invisible to the human eye. Under the microscope "it is like watching birds in the garden." We learnt about how micro-organisms help breakdown minerals, making them more bio-available to plants. They are holding nutrients in a way that is alive.It was fascinating to see some nematodes wiggling around as well as testate amoeba. For both the humanure and compost samples, Hari encouraged adding. a wider range of ingredients for example leaf mould and wood chip to encourage micro-organism diversity.

To finish up, we returned to the garden and held a closing ritual around the compost heap to appreciate compost and soil.

Online workshop

In Part 2 of the workshop, we met online to discuss the results of the contaminant tests and what we found during our time at the garden. Hari opened the call sharing some video footage of our samples taken from under the microscope. We saw nematodes twisting and bending and flagellates floating.

Looking under the microscope at a nematode

We then moved to reflect on key lessons from the in-person workshop. One person reflected on how they wondered what the worms might think of us looking at them. Another reflected on how they felt threads of the composting workshop wove together, gathering like hairs on the legs of a creature. Someone else reflected on how they were struck by the diversity of the compost heap and how they saw this mirrored in the diversity of people in the garden.

We then switched to the soil analysis. Olly reflected how the smell, aggregation and colour of soil samples are important indicators of a healthy soil. Aggregation of soil around plant root systems is also a generally good sign suggesting mycorrhizal networks.

Soil sample: results

Olly had conducted a number of soil sample. We learnt that our soil in general, was on slightly acidic. More acidic soils can mean certain nutrients are inaccessible or not bio-available. We also discovered that there were quite low phosphorous and potassium levels in the orchards. Olly and Hari explained how phosphorous can be important for nutrient cycling and budding but can be bound up in the soil making it difficult for plants to reach it. Potassium is also important for yield, particularly of fruits.

We explored potential ways of raising the phosphorous and potassium on site. Some participants sugested blood, fish and bone and compost teas. The addition of lime was also considered. Then Hari suggested a nifty bio-hack: that the collection of urine from the compost toilet via a plumbing hack could help raise the pH and support the bioavailability of phosphorous and potassium. And luckily there was a plumber in our midst!

We also discussed the compost heap and humanure pile. The samples taken indicated that both had a relatively low iversity of micorrhizal activity. Hari recommended increasing the carbon ratio in our compost heap and humanure chamber, including via the addition of well-decomposed leaf mould and wood chip, to activate the fungal mirco-organisms and diversify the micro-organisms present.

Finally, we considered the outcomes of the lead level tests. The soil samples indicated low levels of lead present in our soils, though not in the compost heap or humanure. Hari encouraged us to increase our application of compost to the veg beds since compost can have a positive effect, reducing uptake into crops.

Creating a compost action plan

We worked together to create an action plan for the bio-hack of the compost loo and action on the compost heap and humanure pile. To conclude, we agreed that it would be great to welcome Harry and Olly back in a year to see if any of these amendments have made a difference to our compost.

With huge thanks to the Lottery for making this workshop possible.


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