SoilSoil Composition

Biochar-Mineral Complex and Compost Influences Soil Bacteria and Quality

Biochar is a carbon rich substance produced from pyrolysis-a process involving thermal degradation of biomass (such as manure, leaves, wood) in the absence of oxygen. It is used as a soil enhancer in agriculture because it has the capacity to enhance crop growth by retaining nutrients in the soil for crop uptake (1,2,3). Biochar is also gaining popularity because it has the potential to reduce emission of nitrous-oxide a potent greenhouse gas from soil (4).

The idea of using pyrolysed biomass as a soil enhancer, originates from old traditional soil management practices in the Amazon basin which produced the famous fertile Amazonian dark earth (10). It is speculated that practices such as cooking fires and intentional spread of charcoal on soil by the natives of this region led to the accumulation of its rich dark earth (1, 10). Biochar also occurs naturally in soils affected by vegetation fires (1).

Biochar can be enriched when mixed with manures, clay and minerals (5,9). Enriched biochar is high in exchangeable cations such as; (calcium (Ca2+), magnesium (Mg2+), sodium (Na+) and potassium (K+); high in plant available phosphorus and it also has a high acid neutralizing ability (9). Recently, a study by scientists in Australia and China (5) looked at the effects of biochar-mineral complexes (biochar coated with minerals) combined with compost (poultry manure) on soil bacteria, soil quality and some plant growth properties for Pakchoi (Brassica rapa L. spp. chinenesis). This article summarises the methodology and some interesting results of this study.


• Seeds were sown: Pakchoi seeds were sown into pots filled with soil, biochar mineral complex (BMC), compost (CO) or biochar mineral complex combined with compost (BMCO). Plants were grown in a growth controlled chamber and were harvested 40 days after planting. Soil and plant samples were then collected for analysis.

• Some soil and plant properties measured: Soil moisture was measured by drying the harvested soil at 60°C for 4 days. Other soil properties measured include soil pH, electrical conductivity, total soluble nitrogen, nitrate, ammonium, organic carbon, available potassium and available phosphate content. Soil microbial analysis was carried out by DNA extraction and sequencing. The plant fresh and dry weight, the leaf area, leaf height and leaf chlorophyll content were also measured. The effects of compost, biochar mineral complex or biochar mineral complex combined with compost on the measured properties were analysed using statistical methods; principal coordinates analysis, permutational analysis of variance, and analysis of variance.

Some results of the study

• Biochar mineral complex combined with compost (BMCO) increased bacteria population and nutrient levels of the soil. They attributed this increase to the presence of compost in the mixture; as organic manure applied to soil increases microbial population (6,7).

• Comparing the compost only treatments to BMCO there was a higher content of total soluble nitrogen, organic carbon, nitrate and available potassium in the BMCO than the compost. In particular, soil nitrate was double the amount in BMCO than in the compost pots. They explained that the increased nitrate levels in BMCO, were as a result of increased soil nitrification caused by the abundance of nitrifying bacteria. Nitrification is a process in the nitrogen cycle which ends with the release of nitrate (the plant available form of nitrogen) in soil.

See- for detailed results.

• Plants grown in BMCO filled pots showed increased leaf size. The authors suggested that the increased leaf size in these plants were as a result of increased nitrate levels caused by BMCO.

• BMCO did not increase the level of available phosphate required for plant growth. They explained that the high pH levels of compost and ions in BMCO might have restricted the availability of this nutrient (see Cao and Harris, 2010; for further reading).

This work indicates that BMC (biochar mineral complex) can combine successfully with organic manure to increase soil microbial population and soil nutrient levels which in turn boosts crop growth and soil quality. The benefits of this combination will lead to a rise in the demand for biochar used in organic farming.

References and further reading

1. What is biochar?

2. Brennan RB, Healy MG, Fenton O, Lanigan GJ (2015) The Effect of Chemical Amendments Used for Phosphorus Abatement on Greenhouse Gas and Ammonia Emissions from Dairy Cattle Slurry: Synergies and Pollution Swapping. PLOS ONE accessed 16th November 2015

3. Clough TJ, Condron LM, Kammann C, Müller C (2013) A Review of Biochar and Soil Nitrogen Dynamics Agronomy 3:275-293.

4. Cayuela ML, Sa´nchez-Monedero MA, Roig A, Hanley K, Enders A, Lehmann J (2013) Biochar and denitrification in soils: when, how much and why does biochar reduce N2O emissions? Scientific Reports 3 : 1732.

5. Ye et al (2016) A Combination of Biochar–Mineral Complexes and Compost Improves Soil Bacterial Processes, Soil Quality, and Plant Properties. Frontiers in Microbiology 7: 372.

6. Hartman et al (2015) Distinct soil microbial diversity under long-term organic and conventional farming. ISME Journal 9: 1177-1194.

7. Zhen et al (2014) Effects of Manure Compost Application on Soil Microbial Community Diversity and Soil Microenvironments in a Temperate Cropland in China.

8. Cao X and Harris W (2010) Properties of dairy-manure-derived biochar pertinent to its potential use in remediation. Bioresource Technology 101:545-553.

9. Chia et al (2014) Characterization of an enriched biochar. Journal of Analytical and Applied Pyrolysis 108:26-34.

10. A brief history of biochar-

Feature Image: Biochar.jpg Via wiki.


    1. In permaculture practice ,mostly waste bio mass from plants that has probably been used in all possible ways, will be used for char production…. The char will then be applied to soils that will probably bee permanent perennial oxygen producing plants…. This can hardly be compared to deforestation for the sake of bio-char production…

    2. The article on ‘beware the biochar initiative’, makes ludicrous claims that biochar in soil will lead to depletion of atmospheric oxygen, amongst other equally unfounded and insane conclusions. The author is a discredited scientist with no professional knowledge in the field. Also a bit of a scam artist trying to instigate payments for full article referencing it would seem.

    1. Randy there are various ways depending where your biochar was sourced. Some is sold ready to go and you just sprinkle it on and dig it in or cover it with mulch. If you’ve made it then it would ideally be inoculated or ‘charged’ with beneficial micro-organisms and/or organic fertiliser which can be done in many ways…such as spraying with or soaking in worm wee, compost tea, seaweed extract home-made or otherwise. This is most vital if you are dealing with poor or water resistant soils. The easiest way actually is to add the biochar into your compost pile as you make it where it helps hold the moisture and aerate it, as the compost micro-organisms do their thing they colonise the pores of the char and it then gets spread around when you apply the compost.

  1. Interesting read, although I think it should be pointed out that it’s not the same as charcoal or Ash. Terra Preta is produced in an environment with very little oxygen. The intense heat decays the wood which then gives off flammable gases but the carbon. The escaping gasses create a type of charcoal with lots of tiny pores creating an enormous surface area, where bacteria, fungi, nutrients and water can reside.

  2. The idea of biochar is very interesting. I’m a little bit worried, however, about using a product that requires an industrial process to create. Biochar is not the same thing as charcoal, and cannot be made outside of a specialized factory setup. It’s not a closed loop at all, and that makes it difficult for me to support in a permaculture environment. Making your own charcoal creates significant greenhouse gases and is sadly not a good idea – nor is the end result (the charcoal itself) the same. It’s good to hear about the range of options out there, and to think about them and talk about them, but I really think that the end goal of permaculture is using non-industrial products as inputs on your site, and in particular closing the loop by either producing them yourself or sourcing them locally and building your community.

    1. I’m currently completing a BioChar Retort on my coffee farm in Ecuador. I’ve run it once so far, and makes beautiful biochar. Just doing some tweaks to make it more efficient. Many people are doing it outside of “specialized factory setup”. I’m running it between 450-500 C and burning off the gases in an afterburner. I have a lot of scrub brush and trees that I have thinned.

      1. Hey Lee, what design are retort you using? 55gal drum with chimney?
        I’m in Manabi, Ecuador, and have been making tons of the stuff for the last few years. I started using the drum retort, but it can get a bit picky with the feedstock density and moisture content. I highly recommend just making a conical hole in the ground ~2m diamater x 1m deep. Much more forgiving on the feedstock length and moisture content and produces a lot more than a drum retort.

        When funds permit I want to make a 2 sheet kontiki kiln, 1.1m3 volume and allows the steam cleansing and storage of dousing water (for foliar application, its soapy).

  3. What permaculture related books would you recommend. I have Introduction to Permaculture by Mollison that I pour over. What other titles do you recommend in your courses.

  4. A case in point is the proposal of the International Biochar Initiative (IBI). ‘Biochar’ is charcoal produced to be buried in the soil that IBI has been promoting worldwide over the past several years [16] as a means of sequestering carbon from the atmosphere to save the climate and enhance soil fertility. It involves planting fast growing tree and various other crops on hundreds of millions of hectares of ‘spare land’ mostly in developing countries, to be harvested and turned into charcoal in a process that could produce crude oil and gases as low grade fuels. There are many excellent arguments against this initiative [17], but the most decisive is that it will certainly further accelerate deforestation and destruction of other natural ecosystems (identified as ‘spare land’). In the process, it could precipitate an oxygen crisis from which we would never recover [18] (Beware the Biochar Initiative, SiS 44).

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