You have a persistent headache. You reach for paracetamol, and the pain subsides. Problem solved, right? Maybe. But you’ve only treated the symptom. You don’t know if the cause of your headache is dehydration, stress, or something more serious. In medicine, we understand that self-prescribing without a diagnosis is dangerous. So why are we making this exact mistake with biochar?
Search online for “how much biochar to apply,” and you’ll get a generic answer: 2 to 20 tonnes per hectare. That wide range is the agricultural equivalent of “take two pills and hope for the best.” It’s a prescription without a diagnosis, and it ignores the most important patient in the equation—your soil.
Applying biochar without first understanding your soil is like performing surgery in the dark. To determine the right dosage—and just as importantly, the right type of biochar—you must first know what you’re trying to fix.
- Is your soil compacted clay that needs better drainage? Or is it porous sand that can’t hold water? The physical structure and particle size of the biochar you choose should be completely different for each.
- What is your soil’s pH and Cation Exchange Capacity (CEC)? Is it nutrient-deficient or dealing with contamination? Applying an alkaline biochar to an already alkaline soil could be counterproductive, while a high-CEC biochar is essential for nutrient retention in poor soils.
- Is your soil biologically active or dormant? The right biochar can serve as a microbial reef, providing habitat for beneficial fungi and bacteria. The wrong one might do very little to kickstart a depleted ecosystem.
A detailed diagnosis, however, doesn’t always lead to a simple, perfect solution. Sometimes, it leads to a calculated and educated decision about priorities.
This is where soil science begins to resemble advanced medicine. Like a doctor who prescribes a treatment with manageable side effects to address a life-threatening condition, a soil expert may prioritize the most pressing soil health issue over minor concerns.
For example, if your soil analysis shows it’s already slightly alkaline, conventional wisdom suggests avoiding alkaline amendments. However, if the soil is also severely degraded and unable to retain water, an expert might still recommend a carefully selected, wood-derived biochar at a moderate rate.
The urgent need to improve soil structure and water retention can outweigh the risk of a minor, manageable increase in pH—especially since wood biochars typically have a neutral effect and soils often buffer small changes. As in medicine, the key is weighing the benefits against the risks and tailoring the intervention to the specific conditions and needs of the soil.
The right approach, therefore, isn’t to ask for a “dosage.” It’s to get a “prescription” based on a thorough understanding of your soil’s needs and your primary objectives.
Stop asking, “How much biochar should I use?” Start asking, “What does my soil need, and which biochar has the precise properties to deliver it, even if it involves calculated trade-offs?” Treat your soil like a patient. Get the diagnosis before you ask for the prescription.
