This spring we linked up with the Big Biochar experiment, where we planted up some test beds to make some comparisons with different soil treatments.

Anyone who doesn’t know about Biochar needs to look into it and find out some more. A good place to start is with this remarkable Horizon documentary which gives an historical and cultural context as to where the idea originates from, deep in the Amazon more than a 1000 years ago.

Evidence suggests there actually were vast civilizations living in the Amazon, pre 1531 which is when the Spanish first arrived. It is a remarkable chapter in history, almost completely frogotten and the only tangible evidence of this once great civilization is the quality topsoil they left behind, in an area notorious for its poor soils for farming.

Alternatively read Albert Bates’ excellent book, the Biochar Solution.. either way it so turns out that this could be the single most important discovery for centuries! It offers a clean source of energy as well as a potential response to combating climate change, soil depletion and food security. Maybe this is the way to sequestrate carbon from the atmosphere and put it back into the soil in a useful way. So if it is so potentially great as a growing medium then it certainly needs to be tested.

Oca plants harvested from our biochar trial beds

We set up 4 1.2m square test beds and in them grew salad, beetroot and oca. The four beds were treated in the following way:
Bed 1, 1KG of biochar was added as well as a wheel barrow of compost.
Bed 2, We added nothing but there had been compost added the previous year.
Bed 3, We added one wheel barrow of compost.
Bed 4, Had a mineral dust based soil improver added and one wheel barrow of compost.

the rock dust mineral soil improver used on Bed 4

The compost was Cwm Harry soil improver and is homogenised and pasteurised high nitrogen food waste compost produced from local sources.

Due to us having to move gardens and other distractions we didn’t measure the salad and beetroot yield, although visibly there seemed to be a clear improvement in beds 1 and 4.

The main crop we chose was Oca (Oca Oxalis Tuberosa) which we thought would make an ideal plant for comparison, in that it produces a tuber and is late to develop, giving it a long time to develop and is something easy to quantify and weigh. It also originates in latin America, so that also seemed appropriate for a biochar experiment. (Oca is Andean, not Amazonian, but its the right continent!)

The Results:
Bed 1: 1.84 KG of tubers… healthy plants but small tubers than bed 4.
Bed 2: 1.34 KG of tubers… these were the smallest tubers in size but there were lots of them.
Bed 3: 1.54 KG tubers… actually very similar to bed 2, plentiful but quite small tubers.
Bed 4: 1.52 KG of tubers… These were the best looking and largest individual tubers, but the total yield was less than bed 1.

So in terms of overall crop the Biochar bed won.. but it was interesting to note that the rock dust treatment bed, Bed 4 had produced bigger and better looking tubers.

Conclusion; I can’t wait to build long term beds using the compost, the rock dust AND the biochar. The results could be frightening!

Get-Growing volunteers setting up the trial beds back in March