The production of rice husk biochar using slow pyrolysis. Photo: Hachib Mohammad Tusar/UPM and Patuakhali Science and Technology University, Bangladesh
Biochar, a charcoal-like sub-stance derived from agricultural and forest wastes, is gaining recognition as an effective soil amendment that not only enhances plant growth but also helps combat climate change.
This material has captured the attention of environmentally conscious gardeners worldwide.
But what exactly is biochar, and does it live up to the hype?
Unlike regular charcoal used for fuel, biochar is specifically designed to improve soil health and contribute to the fight against climate change.
Biochar is created through a process called pyrolysis, in which various organic waste materials, such as agricultural and forestry residues, animal manure, food and green wastes, and even sewage sludge, are subjected to high temperatures ranging from 350°C to 700°C in an oxygen-limited environment.
This process prevents the materials from turning into ash and releasing greenhouse gases. The resulting biochar is highly porous, lightweight, fine-grained and boasts a large surface area, making it an effective tool for enhancing soil properties.
Due to its large surface area, biochar acts like a magnet, holding onto nutrients and keeping them available for plants. This also reduces nutrient loss caused by leaching or erosion, making it particularly valuable when fertilisers are applied. Additionally, biochar reduces soil compaction, increases water retention and promotes microbial activity, all of which creates a more favourable environment for plant growth.
A Kon-Tiki kiln for biochar DIY production. Photos: Dr Padmini Karananidi
Biochar can be applied to the soil using various methods. It can be mixed with compost or organic fertilisers before application to enhance nutrient availability.
Alternatively, biochar can be directly incorporated into the top 15-30cm of soil by tilling or digging, ensuring even distribution throughout the root zone.
For a less labour-intensive option, biochar can be spread on the soil surface and left to integrate naturally over time through rainfall and biological activity.
When establishing new garden beds or planting areas, biochar can be applied in layers along with soil or compost. It can also be mixed into planting holes or potting soil when transplanting seedlings or planting new crops.
As a top dressing around established plants, biochar can be lightly worked into the soil surface to provide ongoing benefits.
Application rates typically range from 0.5kg to 5kg per square metre, depending on the biochar feedstock, soil conditions and crop requirements.
One of the most appealing aspects of biochar is its long-lasting nature. Unlike organic mulches and fertilisers that decompose relatively quickly and require frequent reapplication, biochar is highly resistant to decomposition.
A cross section of oil palm frond biochar under scanning electron microscopy (SEM) with 1000x magnification.
Biochar can persist in the soil for years or even decades; therefore, biochar needs only to be reapplied occasionally to maintain soil health.
While biochar can benefit all soil types, it is particularly effective when applied to problematic soils.
Degraded soils, highly acidic soils or those containing toxic levels of elements like aluminium can experience significant improvements with biochar application.
However, even well-managed and healthy soils can benefit from biochar to maintain their long-term soil fertility.
Gardeners can purchase ready-made biochar or produce it themselves. While the DIY route may be appealing to some, it is crucial to understand the risks and challenges involved.
Improper biochar production can pose fire hazards and release harmful gases like carbon monoxide and methane. To minimise these risks, proper training in biochar production techniques and adherence to local regulations regarding open burning are essential.
Various DIY methods exist, ranging from traditional earth mounds and pit kilns to modern devices like top-lit updraft stoves, steel retort systems and con-tinuous pyrolysers.
The Kon-Tiki flame curtain kiln, an open-source design, has gained popularity among DIY enthusiasts for its simplicity and affordability.
But for many gardeners, purchasing biochar from reputable sources may prove more convenient, safer and cost-effective than producing it themselves.
When selecting a biochar product, it is important to choose high-quality options that have been properly characterised and tested for their intended use.
Beyond its benefits for soil health, biochar also plays a significant role in mitigating climate change.
By storing carbon in the soil
for hundreds to thousands of years, biochar helps reduce atmospheric carbon dioxide levels.
Moreover, by enhancing soil fertility and crop productivity, biochar can alleviate the pressure to convert additional land for agriculture, thereby helping to prevent deforestation and its associated carbon emissions.
In conclusion, biochar is a valuable tool for gardeners seeking to cultivate healthy soil, support thriving plants and contribute to a more sustainable future.
Assoc Prof Dr Christopher Teh currently heads the Dept of Land Management, Faculty of Agriculture, Universiti Putra Malaysia. His expertise is in soil and water conservation.
