Biochar-Based Fertilization

In 2014, the prevailing scientific literature suggested applying 10–20 tonnes of biochar per hectare to see agronomic effects. We showed that 750 kg/ha of nutrient-enhanced biochar, concentrated in the root zone, consistently increased yields in the tropics — and that the combination with organic nutrients even outperforms biochar with mineral fertiliser loading.

Concentrated Root-Zone Application of Biochar-Based Fertiliser

The concept was born out of necessity. In 2014, the introduction of the Kon-Tiki kiln to Nepal gave farmers access to cheap, self-produced biochar for the first time. In rural settings with little access to mineral fertilisers, the question was how to make that biochar agronomically effective using whatever organic nutrient sources were locally available — animal urine, compost, manure.

The answer broke with the dominant approach of the time. Rather than broadcasting large quantities of raw biochar across the soil surface — the 10–20 t/ha rates common in the experimental literature — the institute developed a method based on three principles: enhance the biochar with organic nutrients before application, apply small quantities (as little as 750 kg/ha), and concentrate the amended substrate in the root zone where plants actively take up nutrients and where soil biology is most responsive.

The results were immediate and consistent. In the first systematic trials in Nepal, nutrient-enhanced biochar applied to the root zone at low dosage produced yield increases of 50–400% across 13 crop species and 21 field trials (Schmidt et al. 2017). A fourfold increase in pumpkin yield at just 1 t/ha (Schmidt et al. 2015) demonstrated that biochar's agronomic value depends on how it is charged and where it is placed, not on how much is added. Across all trials, biochar enhanced with organic nutrients — urine, compost, lacto-fermented plant matter — consistently outperformed biochar loaded with mineral NPK fertiliser. The mechanism was elucidated by Hagemann et al. (2017) in Nature Communications: co-composting creates an organic coating on the biochar surface that fundamentally changes its nutrient retention behaviour and stimulates soil biological activity in ways that mineral loading does not.

The famous pumpkin trial where cow-urine enhanced biochar mixed with compost in the root zone of pumpkin plants produced yields of more than 80 tons per ha, more than double compared to chemical fertilizer.

The method was subsequently validated and scaled across multiple geographies: 80-village trials in Bangladesh demonstrating the feasibility of biochar-based fertiliser production at community scale (Satradhar et al. 2021), white cabbage trials in Germany (Grafmüller et al. 2022), and cocoa root-zone injection in Ghana and Indonesia developed through an industry mandate. In the cocoa work, the principle was adapted to perennial tree crops using injection technology to deliver biochar directly to the root zone, breaking nutrient limitations without disturbing the soil surface. Due to the cost of injection, alternative methods using boreholes and living mulch were tested alongside.

More recent work addresses the practical barrier of handling fine biochar in the field. Grafmüller et al. (2024) developed granulation methods that compress biochar-based fertiliser into pellets suitable for mechanical application, extending the method from manual smallholder systems to mechanised agriculture — while also demonstrating that the granulation process does not generate dioxin contamination.

The concentrated root-zone approach has become the institute's most widely adopted agronomic innovation, now used across three continents in systems ranging from Nepalese subsistence farming to European vegetable production and tropical agroforestry.