Friday, December 20, 2013

Biochar application to Soil

     The effectiveness of applications of composts, animal manures or mineral fertilizers are known to vary significantly whether they are incorporated or surface applied, banded or broadcast (Gherardi and Rengel, 2003), and similar responses can be expected to the method of biochar application. The biophysical responses to the way in which biochar is applied have to be considered, as well as technical feasibility, economic constraints and safety. 

Compost and Biochar

Faster & hotter composting – Reduce Nitrogen loss by up to 50%
Reduce compost emissions – Locks up minerals and nutrients
Makes better quality compost – Reduces compost smells

The basic rule of making a good batch of compost is having the right ratio of carbon and nitrogen. Carbon is classed as any dead or brown biomass like brown leaves, woody mulch, sticks, paper, brown dry grass. Nitrogen is anything green or fresh, kitchen scraps, green grass clippings, fresh animal manure, weeds or anything freshly cut from your garden.
A good carbon nitrogen ratio is 25 parts of carbon to 1 part nitrogen. Have a bucket full of Biochar next to your compost bin, when you add a layer of nitrogen sprinkle two big hand fulls of Biochar over the layer so you end up with the fixed carbon Biochar spread evenly through your compost.
Compost activators will help get the compost bin cooking, some common activators are human urine, yoghurt, worm liquid, compost tea, molasses, honey or a bucket full of compost from your last batch.
Biochar added into composts does not rot or break down, it will bond to nutrients, minerals and will reduce nitrogen loss.

     For example, the properties of fineness (‘dustiness’), spontaneous combustion risk, occasional health risks and very low packing density of biochar may provide specific challenges for safe and cost-effective application to soil. Agricultural productivity is often reported to increase with biochar application to soil, but variability is high and it is not yet clear under what soil and climatic conditions and plant species high or low yields can be expected (Lehmann and Rondon, 2006).

     The type of biochar also plays an important role in its effectiveness, and is itself a function of the type of feedstock and production conditions. Therefore, yield responses are currently difficult to predict, and global patterns need to be identified to move towards an understanding of the crop production potential using biochar.

Biochars produced from different feedstocks (coloured circles) and at different temperature vary in their properties. (source:

Purpose of biochar application
     The purpose of applying biochar to soil mainly falls into four broad categories:
1 -agricultural profitability;
2- management of pollution and eutrophication risk to the environment;
3- restoration of degraded land; and
4 -sequestration of C from the atmosphere.

1- Agricultural profitability
     Reduction of soil acidity, improvements to soil cation exchange capacity (CEC) and pH, water-holding capacity, and improved habitat for beneficial soil microbes are most likely the primary causes of productivity improvements. While some information exists about increases in productivity, very little information is available on profitability. Improved profitability requires costs of improvement to be sufficiently lower than the value of the improved productivity. The technology of biochar use is generally at too early a stage to accurately obtain costs of application.

Cation exchange capacity of biochars as a function of feedstock and in comparison with common soil clay minerals; CECof biochar increases with time by up to orders of magnitude (Krull et al., CSIRO). (source:

2- Managing pollution and eutrophication risk
     Eutrophication is commonly considered as one major aspect of global environmental degradation (Nixon, 1995). From an environmental point of view, it is important to intercept leachable nutrients and pesticides from soil to reduce eutrophication and pollution risks in adjacent water bodies, as well as to reduce the need for fertilizer application that would be required to compensate for such nutrient losses. Biochar shows good evidence for adsorbing nutrients such as phosphate and ammonium (Lehmann et al., 2003; Lehmann, 2007) that may cause eutrophication, as well as adsorbing pesticides before they enter local water sources (Takagi and Yoshida, 2003). 

     Location of the biochar within the root zone is required for the interception of nutrients leached to lower soil depths, and deeper application may be desirable. However, nutrients transported by overland flow may require biochar application close to the surface in buffer zones around water bodies at risk in order to maximize contact between runoff and biochar. Therefore, different environmental management techniques require different application methods.

3- Re-vegetation of degraded land
     Re-vegetation efforts for degraded lands may use biochar as a carrier for beneficial soil microorganisms, for improved CEC, and possibly for soil aggregation and water-holding capacity. Since re-vegetation includes reclamation of denuded landscapes, biochar application offers the ability to enhance soil functions in advance of accumulation of plant litter that would otherwise provide the source of soil organic matter under climax vegetation. The scale of re-vegetation and the availability of labor will influence the methods of application. In some instances, such as during the reclamation of mine spoils, it may be necessary to rebuild the entire soil through thorough mixing.

4- Sequestration of C from the atmosphere
     Most carbon in the soil is lost as greenhouse gas (carbon dioxide, CO2) into the atmosphere if natural ecosystems are converted to agricultural land. Soils contain 3.3 times more carbon than the atmosphere and 4.5 times more than plants and animals on earth (1). This makes soils an important source of greenhouse gases but also a potential sink if right management is applied. The use of crop residues for bio-energy production reduces the carbon stocks in cropland. Further the dedication of cropland to bio-fuel production increases the area of cultivated land and thus carbon loss from soils and vegetation.

     Pyrolysis of waste biomass can generate fuels and biochar recalcitrant against decomposition. If biochar is returned to agricultural land it can increase the soil’s carbon content permanently and would establish a carbon sink for atmospheric CO2. In this case the use of crop residues as a potential energy source may improve soil quality and reduce greenhouse gas emissions in a complementary not competing way. Biochar is proposed as a soil amendment in environments with low carbon sequestration capacity and previously depleted soils (especially in the Tropics). 

  1. Extracting fossil fuel from the earth and burning it puts CO2 into the air.
  2. Growing biomass pulls COfrom the air and incorporates it into itself.
  3. When the plants die, they decompose and the CO2 returns to the atmosphere.
  4. As an alternative to decomposition, the biomass is pyrolyzed.
  5. The biochar does not decompose and so stays out of the atmosphere.

    From previous studies it is known that soil biochar amendments increase and maintain soil fertility (2) and the human-made Terra Preta soils in the Ama-zon prove that infertile soils can be transformed into fertile soils and long term carbon enrichment is feasible even in environments with low carbon sequestration capacity (3).

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