Swansea Biochar, Our System
(page under construction)
A small forest garden is slowly becoming more established. We have raised salad beds, a couple of polytunnels for plant raising and for growing on half hardy crops in our terraced hugelbeds and grazing for the horses. The main focus is on the annual vegetable field.
In this area of high rainfall and with sandy soil, a lot of manure has been incorporated into the soil here over the years. However, it is the manure rather than the soil that has been allowing vegetable production to happen. The soil structure was being damaged by cultivation, the soiul was becoming increasingly degraded and nutrients were being lost from the manure as pollution.
Having taken a couple of years away from growing vegetables, perennial weeds have become well established. I now do things differently.
A constant trickle of biochar is now going into the field via the horses stables, where it provides a hygenic bedding, is crushed and absorbs nitrates and other nutrients from the horses urine and manure.
We are aiming to establish a closed loop carbon negative system, no outside inputs and plants on site drawing down carbon and nitrogen. However, a few tree surgeon friends are having to pay municipal charges to dispose of their chipped wood and waste logs. We let them drop these off here for no charge as this speeds up the process of getting a rich, black, stable medium in which to grow crops.
We avoid digging the soil because digging has the following effects:
Digging exposes the soil particles to increased air. This increased soil air allows a proliferation of soil bacteria (acinobacteria) which makes nutrients available to crops, which is why digging can result in increased cropping. This comes at a cost: the proliferation of bacteria also release soil carbon into the atmosphere as CO2. We want that carbon in our soil and so we avoid digging. (We dig only to plant and to harvest potatoes).
Digging breaks the fungal mycelial networks in the soil. The strands of mycelia are often invisible to the naked eye and we want certain types of mycelia because they can act as plant root extenions, bringing nutrients from beyond the root zone to plants and they can stabilise carbon in the soil as glomalin.
Digging breaks soil aggregates not only by encouraging a proliferation of acinobacteria but also by mechanically destroying the aggregates. Strong aggregate properties of soil are necessary to protect soil from erosion.
Digging is usually done to kill weeds. Instead of digging, we use the permaculture trick of deep mulching. We are trying to overcome the problem of pollution as the mulch decomposes through tactical use of biochar.
We clear established perennial weeds including dock weeds, couch grass, bind weed and creeping thistles by covering them with a thick layer of fresh wood chips. (or again use leaves, sticks and coppice if you do not have a supply of wood chip).
The light is blocked, killing annuals and weakening perennials. Nitrate robbery is the key here; the wood chip robs the weeds of nitrates. This layer is left for a year and any weeds which poke their heads up through the mulch are cut down with a mattock.
After a year, any weeds that do blow in and germinate can be easily pulled out of the decomposing mulch by hand as the tilth is now getting better.
Paths are now marked and dug between the beds and stepping stones (or logs) are placed along the beds so as to reduce the temptation for people to walk on the beds. Walking would dammage the aggregate structure of the mulch and it would be prone to weathering.
Warning: Do not disturb piles of woodchip or grass cuttings if fungal spores are present. The piles will be warming up and you will see fungal spores in the air if they are present when you disturb it. These can cause ‘farmers lung’ and lead to serious illness. Either handle them when very fresh or leave them for a few weeks until the spores are no longer visible when disturbed.
Stabilise That Mulch
It is hard work wheelbarrowing wood chip and it will simply go back into the sky mainly as CO2 from where the trees took it from if it is not stabilised.
This is where the biochar comes in. Tera pretta is 9% biochar and much of the remining organic matter has not decomposed bacterially, the organic matter can be identified today, centuries after it was put into the soil.
Planting and Growing
We use a 5 year rotation in most of our annual vegetable field;
year 1, potatoes. Year 2, brassicae. Year 3, alliums. Year 4, Roots. Year 5, Three sisters (legumes, squashes and corn).
The beds get dug one year in every 5, when the potatoes are planted and again when they are harvested. Because this is when we dig, this is also when we add the biochar. (Remember, neat biochar will rob the already nitrate hungry mulch of more nitrates. Nutritionally activate it first).
The best way to know how much biochar to add is to buy a simple probe pH metre and add biochar incrementally keeping an ey on the changing pH as the wood decomposes. The biochar often has a slight alkalising effect, depending on the type of wood used to make it.
It is easy to plant a large area of potatoes using only a mattock as you are not digging into the soil, only to the bottom of the mulch. As they are planted, cover them in biochar ammended compost before ridging up. A small spade makes light work of ridging up the potato seeds.
As the potatoes
Using biochar to optimise AMF.
Research on the interaction between biochar and AMF shows that the biochar can enhance AMF activity but that there are some conditions where adding biochar can inhibit it. It is important to understand the criteria needed in order for this relationship to be positive.
In order to ensure the liklehood of a positive relationala between biochar and AMF:
1, The biochar should be produced at temperatures of between 450 and 500 centigrade.
2, The biochar should be made of herbaceous rather than non herbaceous material (for example brush rather than nut kernals)
3, The biochar should be crushed before use.
Beyond this there is very little scientific research and virtually no other field examples of practices which use biochar in a growing system to encourage AMF activity.
Another technique we use is to grow a crop of green manures on the composting piles of biomass and biochar. It is hoped yhat the roots of the green manure crops allow and encourage the symbiosis with the AMF thus stabilising carbon in the composting biomass and hopefully establishing AMF in the compost prior to application. Again, this has not been experimentally tested and so we do not know to what extent it works.
Heat for the polytunnel, cooking and hot water (as well as that produced by composting
the RCW) is produced by either tlud stoves (outdoor cooking) or rocket hybrid stoves (indoor use, in conjunction with multi purpose heaters), in order to produce a continuous flow of biochar whilst maximising energy capture.
We aim to keep permanent live plant roots present in both the annual and perennial no dig vegetable plots. This ensures that the symbiosis between AM and plants can be supported. In the annual vegetable beds, annual winter hardy green manures are sown into the mulch prior to harvesting the vegetables and rows of perennial herbs are grown between the crops.
The reasons for aiming to promote AMF rather than bacterial activity and to determine whether crop quality can be maintained under conditions which promote AMF are:
1, Stabilising carbon in soil in the form of glomalin reverses climate change.
2, The presence of stable carbon in the soil protects soil from erosion by increasing its binding and exchange capacaties.
3, Similarly, the glomalin maintains soil fertility by ‘glueing’ (forming agregates) and thereby maintaining the presence of organic matter, possibly including biochar, in soils.
4, The reduced bacterial activity (by not aerating or fertilising soil) will reduce pollutants such as nitrates from being released to ground water and the atmosphere.
5, The production of soluble nitrate and other fertilisers requires large energy inputs, produced by burning fossil fuels. Peak oil, climate change and consequent food security issues dictate that we have to find alternative ways of growing food. Rather than feeding the plants with fertilisers, AMF have the effect of bringing distant nutrients in soil to the plant.
4, By encouraging AMF rather than using conventional growing practices and fertilisers, food has a greater nitritional value. This is because the AMF bring more than just nitrogen, phospherous and potassium to the plant, they bring a wide range of minerals and nutrients as required by the plant.