Biochar Pros & Cons In Gardens

Biochar Isn’t New, So What Are The Biochar Pros & Cons In Gardens & Horticulture? In This Article Discover What Biochar Is, It’s Benefits & Disadvantages & How Amazon Tribes Used This Modern Form Of Charcoal To Grow Food.

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In this article I am discussing the obvious Biochar Pros & Cons In Gardens & Horticulture. But much about biochar isn’t obvious or simple. Research is ongoing in universities, and at horticultural research stations, but much is yet to be learnt. For example, advocates claim that biochar has been used by Amazon tribes for hundreds of years AND that it needs technically advanced processes for its manufacture. But no one has explained to me how the Amazon tribes discovered and used technically advanced processes! It sounds a bit like biochar BS to me.

Perhaps the truth is that biochar doesn’t necessarily need to be manufactured using advanced technology. I believe we are trying to build mystic around a very common product that has been around for thousands of years. That product is charcoal. It’s not that I can’t see value in biochar and believe is has uses. It’s just that some people seem to want to make it a wonder product. A bit like they want to make some vegetables into superfoods!

So let’s examine what biochar really is.

What Is Biochar?

Biochar is organic material that has been heated to high temperature, with little or no oxygen, to carbonise it. And broadly speaking that is the same definition as we could use to describe charcoal. Practically speaking biochar is a form of charcoal. There are minor differences, but only minor differences as described below.

Difference Between Biochar and Charcoal

Let’s start with charcoal. It’s been around for millennia. The technological advances made during the Bronze and Iron Ages could not have happened without charcoal. To make bronze and iron, the high temperatures reached in a charcoal fire were essential.

So charcoal isn’t new. It is traditionally produced by building a mound of organic matter (usually wood) and burning it slowly with reduced levels of oxygen. The usual way of doing this was to cover the clamp of wood with soil so that no oxygen could enter. The high temperatures in the clamp (or later charcoal towers) drove off the volatile gases and left behind the carbon as charcoal.

The yield was around 60% by weight based on the weight of the original organic matter. Today charcoal is made in a retort of various designs, which exclude more oxygen, and the yields are higher.

Biochar is made in a similar way to modern charcoal. The process sis often described as pyrolysis. But all pyrolysis means is to separate by using heat. In this case to drive off the volatile gases and leave behind the carbon. It’s essentially the same process. BUT more efficient.

Modern technology does it better than the old processes. And purists argue that biochar is produced as a soil amendment rather than for the multitude of uses that charcoal has. But in reality there is little difference except the process is more efficient.

The difference the purists would however argue is that biochar is usually a finely powdered product than lump charcoal and that the pore sizes in biochar are larger. That does make a difference as I explain later but it’s a subtle difference by most measures.

Why Is Biochar Used In Soils?

The must common claims are that biochar : –

Improves crop yields,
Improves plant health
Neutralises soil acidity,
Provides improved water and nutrient retention (especially in sandy soils)
Sequesters carbon
Improves drainage
Improves soil aeration
Improves soil porosity
Reduces greenhouse gas (GHG) emissions
Immobilises heavy metals in the soil.

I am not convinced that all of these are true, but could be convinced by verifiable research and /or other evidence. For example any soil acidity reduction is likely to be minimal when relatively small amounts of biochar are added to a soil. The dilution effect is likely to nullify the impact.

However, biochar can be added in a highly porous finely ground product so we need to take the large surface area into account.

How Is Biochar Used in Gardening & Horticulture?

An American site I have read suggests that biochar need “charging” with compost to ensure it has the microbiology (sic) needed to ensure it works properly.

It goes on to suggest that gardeners use 5-10% biochar in the top 6 inches of their soil. I’m not sure if this is 5-10% by volume or weight which is important as biochar is quite light.

I take this with a pinch of charcoal as they manufacture biochar, so “they would say that wouldn’t they?”

The cost would be prohibitive to most gardeners.

When it comes to Biochar Pros & Cons In Gardens & Horticulture I’d say this is a definitive con!

What Does Biochar Cost?

It’s not cheap. But let’s look at what I might have to pay to use it in my own garden.

In my garden I would need a huge amount of biochar. Even if I look at a small bed measuring, say, 3×1 yard I’d need around a third of a cubic yard of biochar. I’ve five veg beds that size. So I’d need just under two cubic yards of biochar.

In America they charge $600 for a cubic yard. Allowing for local delivery (and the exchange rate) we are talking about it costing me around £70 square yard of bed. So around £1000 for my tiny little veg garden.

Biochar Use By Amazonian Tribes

Going before Christopher Columbus sailed across the Atlantic to the Americas the native tribes of the Amazon region were using biochar. They smouldered organic waste in pits, covered with soil, and disposed of the residues on their soils. The Portuguese were later to call these soils “terra preta” (‘black earth’ in Portuguese). This practice seems to go back at least 2000 years.

Whether the native people understood the science behind their use of these residues I can’t say. Whether they even did it to improve soils we can only speculate. Some might attribute the biochar to slash and burn agriculture. But the fact it often contains pottery shards makes this doubtful in my mind.

The biochar found in the Amazon has been observed to be finely powdered and it has been hypothesised that the Amazonian earthworm Pontoscolex corethrurus , was the main agent of fine powdering and incorporation of charcoal debris in the Amazonian soils.

I’ve used the term biochar in this section but clearly where the organic material was burnt in trenches no greatly advanced technology was being used. The product of such a burn was more likely to one a crude charcoal rather than refined biochar. And it was the action of the earthworms, time and nature degradation tha produced the finely powdered final product.

The Future For Biochar

I believe the future for biochar is potentially good. The research to date is mixed but promises much and The Intergovernmental Panel on Climate Change (IPCC) see biochar, with it’s its long-term carbon sequestration potential, as one of the solutions to fight climate change, thanks to its long-term carbon sequestration potential and its multiple co-benefits.